Aberrant Levels of miRNAs in Bone Marrow Microenvironment and Peripheral Blood of Myeloma Patients and Disease Progression

The bone marrow (BM) microenvironment of multiple myeloma (MM) is reported to play a role in the biology of disease. In this study, we found that the extracellular BM microenvironment in MM contains a unique miRNA signature detectable by miRNA microarray and quantitative real-time PCR, which is partially represented in the peripheral blood. Eleven miRNAs were significantly decreased in both BM and serum of MM patients in comparison with controls. Evaluation of these miRNAs in plasma of a separate cohort of MM patients and controls confirmed significantly aberrant levels of let-7a, let-7b, let-7i, miR-15b, miR-16, and miR-20a in both serum and plasma. We then studied the myeloma precursor diseases and found that a subset of the MM miRNAs exhibited aberrant expression in monoclonal gammopathy of undetermined significance and smoldering myeloma. miRNA analysis of enriched CD138(+) plasma cells from MM and monoclonal gammopathy of undetermined significance found that most of the validated MM BM signature miRNAs were significantly decreased in MM plasma cells. Gene expression profiling indicated that multiple targets of the decreased miRNAs found increased expression in MM plasma cells, including ATF2, HRAS, HDAC4, TGFB1, TGFBR1, and mitogen-activated protein kinases. The findings suggest that these miRNAs are detectable in aberrant levels in the peripheral blood of patients with plasma cell proliferation and may play a role in aberrant plasma cell proliferation and disease progression.

Scavenger receptor-BI is a receptor for lipoprotein(a)

Scavenger receptor class B type I (SR-BI) is a multi-ligand receptor that binds a variety of lipoproteins, including high density lipoprotein (HDL) and low density lipoprotein (LDL), but lipoprotein(a) [Lp(a)] has not been investigated as a possible ligand. Stable cell lines (HEK293 and HeLa) expressing human SR-BI were incubated with protein- or lipid-labeled Lp(a) to investigate SR-BI-dependent Lp(a) cell association. SR-BI expression enhanced the association of both (125)I- and Alexa Fluor-labeled protein from Lp(a). By confocal microscopy, SR-BI was also found to promote the internalization of fluorescent lipids (BODIPY-cholesteryl ester (CE)- and DiI-labeled) from Lp(a), and by immunocytochemistry the cellular internalization of apolipoprotein(a) and apolipoprotein B. When dual-labeled ((3)H-cholesteryl ether,(125)I-protein) Lp(a) was added to cells expressing SR-BI, there was a greater relative increase in lipid uptake over protein, indicating that SR-BI mediates selective lipid uptake from Lp(a). Compared with C57BL/6 control mice, transgenic mice overexpressing human SR-BI in liver were found to have increased plasma clearance of (3)H-CE-Lp(a), whereas mouse scavenger receptor class B type I knockout (Sr-b1-KO) mice had decreased plasma clearance (fractional catabolic rate: 0.63 ± 0.08/day, 1.64 ± 0.62/day, and 4.64 ± 0.40/day for Sr-b1-KO, C57BL/6, and human scavenger receptor class B type I transgenic mice, respectively). We conclude that Lp(a) is a novel ligand for SR-BI and that SR-BI mediates selective uptake of Lp(a)-associated lipids.

Hypermutation of ApoB mRNA by rat APOBEC-1 overexpression mimics APOBEC-3 hypermutation

APOBEC-3 proteins induce C-to-U hypermutations in the viral genome of various viruses and have broad antiviral activity. Generally, only a small proportion of viral genomes (<10(-)(2)) are hypermutated by APOBEC-3s, but often many cytidines (up to 40%) are converted into uridine. The mechanism of this unique selective hypermutation remains unknown. We found that rat APOBEC-1 overexpression had a hypermutation pattern similar to that of APOBEC-3s on its substrate apolipoprotein B (apoB) mRNA. Transient plasmid transfection of rat APOBEC-1 resulted in 0.4% and 1.8% hypermutations with apoB mRNA in HepG2 and McA7777 cells, respectively. The low frequency of hypermutated apoB mRNA targets was enriched by differential DNA denaturation PCR at 72-76 °C, with hypermutation levels increasing up to 67%. Up to 69.6% of cytidines in HepG2 and up to 75.5% of cytidines in McA7777 cells were converted into uridines in the hypermutated apoB mRNA. When rat APOBEC-1 was overexpressed by adenovirus, the hypermutation frequency of apoB mRNA increased from 0.4% to ∼20% and was readily detected by regular PCR. However, this higher expression efficiency only increased the frequency of hypermutation, not the number of affected cytidines in hypermutated targets. Rat APOBEC-1 hypermutation was modulated by cofactors and eliminated by an E181Q mutation, indicating the role of cofactors in hypermutation. The finding of an APOBEC-3 hypermutation pattern with rat APOBEC-1 suggests that cofactors could also be involved in APOBEC-3 hypermutation. Using hepatitis B virus hypermutation, we found that KSRP increased APOBEC-3C and APOBEC-3B hypermutation. These data show that, like rat APOBEC-1 hypermutation, cellular factors may play a regulatory role in APOBEC-3 hypermutation.

Comparison of anti-CD3 and anti-CD28-coated beads with soluble anti-CD3 for expanding human T cells: differing impact on CD8 T cell phenotype and responsiveness to restimulation

Background

The ability to expand virus- or tumor-specific T cells without damaging their functional capabilities is critical for success adoptive transfer immunotherapy of patients with opportunistic infection or tumor. Careful comparisons can help identify expansion methods better suited for particular clinical settings and identify recurrent deficiencies requiring new innovation.

Methods

We compared the efficacy of magnetic beads coated with anti-CD3 and anti-CD28 (anti-CD3/CD28 beads), and soluble anti-CD3 plus mixed mononuclear cells (designated a rapid expansion protocol or REP) in expanding normal human T cells.

Results

Both anti-CD3/CD28 beads and soluble anti-CD3 promoted extensive expansion. Beads stimulated greater CD4 cell growth (geometric mean of 56- versus 27-fold (p < 0.01) at day 21) but both stimulated similar CD8 expansion (189- versus 186-fold). Phenotypically, bead-treated CD4 and CD8 T cells and anti-CD3-treated CD4 cells typically assumed an effector/effector memory phenotype by day 14. By comparison, a subset of anti-CD3-treated CD8 cells, derived from naïve cells, retained much greater expression of CD45RA, CD27 and CCR7, than matched bead-treated cells despite comparable expansion. These cells were clearly distinguishable from CD45RA+ terminally differentiated effector cells by the presence of CD27, the absence of CD57 and their inability to produce cytokines after stimulation. When used to expand previously stimulated cells, anti-CD3 plus autologous MNCs produced much less antigen-induced cell death of CD8 cells and significantly more CD8 expansion than beads.

Conclusions

Anti-CD3/CD28 beads are highly effective for expanding CD4 cells, but soluble anti-CD3 has significant potential advantages for expanding CD8 T cells, particularly where preservation of phenotypically "young" CD8 cells would be desirable, or where the T cells of interest have been antigen-stimulated in vitro or in vivo in the recent past.

Effect of ex vivo culture duration on phenotype and cytokine production by mature dendritic cells derived from peripheral blood monocytes

BACKGROUND

To generate clinical-grade dendritic cells (DCs) ex vivo for immunotherapy trials, peripheral blood monocytes are typically cultured in granulocyte-macrophage-colony-stimulating factor (GM-CSF) and interleukin (IL)-4 and then matured using one or more agents. Duration of the initial DC culture is one important variable that has not been systematically evaluated for its effect on the characteristics of the final mature DC product.

STUDY DESIGN

DCs were generated from elutriated peripheral blood monocytes by incubation in medium containing 2000 units per mL each of GM-CSF and IL-4 for 3 to 7 days, followed by maturation with lipopolysaccharide and interferon-gamma (IFN-gamma). DC yield, viability, flow cytometric phenotype, and cytokine production were evaluated.

RESULTS

The percentage yield and viability of mature DCs were similar after GM-CSF/IL-4 culture for 3 or 7 days. In either case, mature DCs expressed abundant CD80, CD86, CD83, and CCR7, but 3-day DCs expressed these antigens in a more consistent and homogeneous manner. Mature 3-day DCs produced much more IL-12 and less IL-10 after restimulation with CD40L-LTK than 7-day DCs. The former were also more effective in presenting immunogenic peptides to CD8 T cells. Analogous changes in cytokine production were observed in mature DCs prepared using lower concentrations of GM-CSF/IL-4 or when the alternative maturation cocktails poly(I:C)/IFN-gamma and soluble CD40L/IFN-gamma were used.

CONCLUSION

Extended initial culture of DCs in GM-CSF/IL-4 does not affect yield or viability of subsequently matured DCs, but can adversely affect their ability to homogeneously express high levels of functionally important surface molecules such as CD83 and CCR7 and to produce IL-12.

A functional comparison of mature human dendritic cells prepared in fluorinated ethylene-propylene bags or polystyrene flasks

BACKGROUND

Fluorinated ethylene-propylene (FEP) bags have been used instead of polystyrene (PS) flasks for ex vivo clinical-scale production of human dendritic cells (DCs) to facilitate closed-system recovery of these highly adherent cells. To assess the impact of DC culture on this nonadherent surface, the function of DCs generated in FEP and PS was compared.

STUDY DESIGN AND METHODS

Cell yield, phenotype, cytokine production, migration, and antigen-presenting activity were measured in DCs prepared from peripheral blood monocytes in FEP bags or PS flasks with medium supplemented with serum, interleukin (IL)-4, and granulocyte-macrophage-colony-stimulating factor for 5 days to induce DC differentiation and CD40L or poly(I:C) plus interferon-gamma to promote maturation.

RESULTS

DCs cultured in FEP or PS had comparable cell yield, viability, and CD83 and CCR7 expression. DCs generated in FEP, however, produced significantly less IL-12 and IL-10 during maturation, and differences persisted on rechallenge after harvest. FEP-cultured DCs migrated spontaneously or in response to CCR7 ligand more actively than PS-cultured DCs, but this difference was not significant. Mature DCs prepared in FEP and PS were equipotent in stimulating peptide-specific CD8 T-cell expansion in vitro.

CONCLUSION

FEP- and PS-cultured DCs are similar in phenotype and in some functional measures, but FEP markedly reduces DC production of IL-12 and IL-10. This phenomenon presumably reflects intracellular changes linked to the absence of a surface for firm cell adherence. Given the importance of these cytokines in the immune response, these changes could have a significant impact on DC function in vivo.

Recombinant lemA without adjuvant induces extensive expansion of H2-M3-restricted CD8 effectors, which can suppress primary listeriosis in mice

Mice infected with Listeria monocytogenes (LM) produce large numbers of H2-M3-restricted CD8 T cells directed against the formylated peptides, f-MIGWII and f-MIVIL. To examine responsiveness to these epitopes in the absence of infection, we inoculated mice with recombinant lemA (r-lemA) containing f-MIGWII or r-vemA (a variant of r-lemA containing f-MIVIL in place of f-MIGWII) without adjuvant. To monitor responses, we measured peptide-specific cytoplasmic IFN-gamma production ex vivo by freshly harvested splenocytes at varying times post-inoculation. B6 mice inoculated with r-lemA produced substantial numbers of epitope-specific CD8 cells with peak levels on day 7 when there were 1.1 x 10(6) f-MIGWII-specific CD8 cells in the spleen (8.2% of total CD8 splenocytes). The r-vemA-treated animals accumulated 0.25 x 10(6) cells (1.8% of total CD8 cells) at this time point. Comparable responses were observed after rechallenge of immunized animals. Other elements in the lemA moiety distinct from the immunogenic peptide were required since mice did not respond to equimolar amounts of synthetic f-MIGWII or f-MIVIL alone. In comparative studies, B6 and C3H/HeJ mice responded to r-lemA much more vigorously than BALB/c animals. When r-lemA- or r-vemA-treated B6 animals were challenged i.v. with LM 7 days later, they suppressed splenic accumulation of bacteria much more effectively than controls. On the other hand, antigen-treated animals were not protected against infection 1 month later. Thus, responsive strains of mice respond vigorously to H2-M3-restricted epitopes, even in the absence of bacterial infection or adjuvant. The resulting effectors acutely enhance antimicrobial resistance but do not confer long-term memory protection.

The adjacent flanking region plays a critical role in facilitating the presentation of the Listeria monocytogenes product lemA to H2 M3wt-restricted, peptide-specific murine CD8 cells

Mice infected with Listeria monocytogenes (LM) generate CD8 effectors specific for f-MIGWII, the amino terminus of the bacterial product lemA presented by the class Ib MHC molecule H2 M3wt. lemA has several distinctive properties: 1) it is readily presented as an exogenous Ag in the absence of bacterial infection; 2) it is processed by a TAP-independent pathway, which is sensitive to chloroquine, pepstatin, and brefeldin; and 3) the immunogenic portion of the molecule is extremely resistant to proteolytic degradation even by proteinase K. To assess the structural basis for these findings, we expressed a truncated variant (t-lemA) containing the amino-terminal hexapeptide and the subsequent 27 amino acids linked to a histidine tail in Escherichia coli, and purified the product by affinity chromatography. Purified t-lemA could be presented to f-MIGWII-specific effectors by macrophages and fibroblasts at 1-10 nM. Unlike f-MIGWII, which binds directly to H2 M3wt, t-lemA required processing by a chloroquine-, pepstatin-, and brefeldin-sensitive pathway. Brefeldin sensitivity often implies endogenous processing in the cytoplasm, but several lines of evidence suggest translocation to the cytoplasm and proteosomal degradation are not critical for t-lemA presentation. Unlike f-MIGWII, t-lemA was profoundly resistant to proteinase K, and, using 35S-labeled t-lemA, we could identify the region from position 1 to approximately 30 as the protease-resistant element. Thus, the hydrophobic peptide sequence following f-MIGWII can account for the unusual properties of lemA noted above. Analogous modification could be used to alter the properties of other peptide Ags presented by class I MHC products.

The Adjacent Flanking Region Plays a Critical Role in Facilitating the Presentation of the Listeria monocytogenes Product lemA to H2 M3wt-Restricted, Peptide-Specific Murine CD8 Cells

Mice infected with Listeria monocytogenes (LM) generate CD8 effectors specific for f-MIGWII, the amino terminus of the bacterial product lemA presented by the class Ib MHC molecule H2 M3wt. lemA has several distinctive properties: 1) it is readily presented as an exogenous Ag in the absence of bacterial infection; 2) it is processed by a TAP-independent pathway, which is sensitive to chloroquine, pepstatin, and brefeldin; and 3) the immunogenic portion of the molecule is extremely resistant to proteolytic degradation even by proteinase K. To assess the structural basis for these findings, we expressed a truncated variant (t-lemA) containing the amino-terminal hexapeptide and the subsequent 27 amino acids linked to a histidine tail in Escherichia coli, and purified the product by affinity chromatography. Purified t-lemA could be presented to f-MIGWII-specific effectors by macrophages and fibroblasts at 1–10 nM. Unlike f-MIGWII, which binds directly to H2 M3wt, t-lemA required processing by a chloroquine-, pepstatin-, and brefeldin-sensitive pathway. Brefeldin sensitivity often implies endogenous processing in the cytoplasm, but several lines of evidence suggest translocation to the cytoplasm and proteosomal degradation are not critical for t-lemA presentation. Unlike f-MIGWII, t-lemA was profoundly resistant to proteinase K, and, using 35S-labeled t-lemA, we could identify the region from position 1 to ∼30 as the protease-resistant element. Thus, the hydrophobic peptide sequence following f-MIGWII can account for the unusual properties of lemA noted above. Analogous modification could be used to alter the properties of other peptide Ags presented by class I MHC products.

Downregulation of T cell receptor expression by CD8(+) lymphocytes in kidney allografts

Allospecific CD8(+) T lymphocytes are an important component of the cellular response in allograft rejection. These cells recognize and engage MHC class I antigens, leading to allospecific cytolytic responses and graft rejection. In mouse kidney allografts that survive to 3 wk after transplantation, we noted that the majority of CD8(+) cells do not express surface alpha/beta T cell receptor alpha/beta(TCR), gamma/deltaTCR, or CD3. However, these CD8(+)TCR- cells did express surface markers characteristic of T cells, including Thy1.2, CD2, and CD5. In addition, the CD8(+)TCR- cells expressed mRNA for TCR Vbeta gene families, and nearly half stained positive for cytoplasmic Vbeta8 protein, suggesting that they are T cells that have downregulated alpha/betaTCR protein expression from their cell surfaces. When these surface TCR- cells were isolated from kidney allografts by flow cytometry and cultured in the presence of either allogeneic or syngeneic stimulators, nearly 100% of cells reacquired normal levels of alpha/betaTCR expression with disproportionate usage of Vbeta8 chains. After recovery of their surface TCR expression, the CD8(+)TCR- population demonstrated strong alloreactivity in culture. These results suggest that the substantial number of CD8(+)TCR- cells found in long-term surviving mouse kidney allografts are alpha/beta-T cells that have downregulated their cell surface expression of TCR. While in other systems this phenotype may identify cells that have engaged antigen, our results indicate that loss of TCR expression by CD8(+) kidney graft-infiltrating cells may not depend on antigen engagement and that elements in the microenvironment of the kidney graft play a key role in this process. Factors that modulate expression of TCR by graft-infiltrating lymphocytes may have an important role in regulating rejection responses.

H2M3wt-restricted, Listeria monocytogenes-immune CD8 T cells respond to multiple formylated peptides and to a variety of gram-positive and gram-negative bacteria

A subset of H2M3wt-restricted, Listeria monocytogenes (LM)-immune CD8 effectors recognize antigen-presenting cells (APC) preincubated with heat-killed LM. The responsible product, which we have previously designated heat-killed Listeria-associated antigen (HAA), is extremely hydrophobic and resistant to proteolytic degradation. Despite the protease resistance of HAA, we now report that HAA-immune clones are uniformly responsive to fMIGWII, a formylated oligopeptide derived from the recently described LM product, lemA. While fMIGWII was by far the most potent peptide tested, over half our clones also responded to the LM-derived peptide fMIVII and cross-reactive responses to two other unrelated formylated peptides at concentrations of <1 microM were frequently observed. One of these peptides (fBlaZ) did not share any amino acid in common with fMIGWII except N-formyl methionine at position 1. Unformylated variants of the same peptides were inactive. HAA-immune CD8 cells also responded in an H2M3wt-restricted manner to APC pretreated with heat-killed or live preparations of other gram-positive and gram-negative bacteria such as Streptococcus pyogenes (SP) and Proteus vulgaris (PV). Unlike fMIGWII which is water soluble and protease sensitive, the native antigens extracted from SP and PV, like HAA, were very hydrophobic and proteinase K resistant, presumably reflecting in each case the association of cross-reactive polypeptides with bacterial lipid or phospholipid. Thus, HAA/lemA-immune, H2M3wt-restricted effectors can respond to a variety of formylated peptides and bacterial antigens in vitro. Similar cross-reactions in vivo might have physiologically significant implications.

CD4+ cytolytic effectors are inefficient in the clearance of Listeria monocytogenes

Cytotoxic T lymphocytes (CTL) recognize and lyse target cells through the interaction of the T-cell receptor complex with the class I or class II major histocompatibility complex (MHC). The production of class I-restricted CTL has been shown to be critical to the elimination of specific pathogens including Listeria monocytogenes. However, the function of class II-restricted CTL in the clearance of intracellular pathogens is poorly understood. H-2b beta 2-microglobulin-deficient mice (beta 2M-/-) are not able to produce CD8+ CTL in response to infection with L. monocytogenes. We used this model to evaluate the efficacy of class II-restricted CTL, in the absence of a class I-restricted response, during a primary infection with L. monocytogenes. We demonstrate that, despite their effectiveness in adoptive transfer of protection, Listeria-specific CD4+ class II-restricted cytotoxic lymphocytes are ineffective in decreasing titres of L. monocytogenes in the spleen was found established infection. In beta 2M-/- mice, persistence of L. monocytogenes in the spleen was found preferentially in class II-negative cells. Surprisingly, class I-restricted CTL from C57BL/6 mice were capable of decreasing bacterial titres during an established infection even in the absence of detectable class I on the surface of cells from beta 2M-/- mice. These data strongly suggest that, in the absence of a class I-restricted response, pathogens that elicit a class II-restricted cytotoxic response may escape prompt eradication by the immune system.

The intragraft CD8+ T cell response in renal allograft rejection in the mouse

To identify the role of donor class I alloantigens in regulating the CD8+ T cell response to a kidney allograft, we analyzed and compared the CD8+ infiltrate in kidney transplants from MHC class I-deficient (class I-) mouse donors and class I+ controls. One week after transplantation, there was a prominent CD8+ infiltrate in control allografts, whereas CD8+ T cells were virtually absent in grafts from class I- donors. In class I+ allografts, infiltrating CD8+ cells utilized a wide range of T cell receptor (TCR) Vbeta families and their Vbeta usage was similar to that of the systemic CD8+ population. However, there was a modest but significant overrepresentation of cells bearing Vbeta8 in the graft compared with the spleen due to an expansion of CD8+ Vbeta8.3+ cells. This could be detected as early as 1 week and became more pronounced by 3 weeks after transplantation. In 3-week allografts, only 52% of CD8+ cells expressed alphabetaTCR. Among T cells isolated from class I+ grafts, the CD8+ Vbeta8+ cells demonstrated allospecific responses that were numerically larger than responses of the CD8+ Vbeta8- population. In contrast to the early (1 week) time point, significant numbers of CD8+ cells could be isolated from class I- grafts by 3 weeks after transplantation and their Vbeta repertoire resembled that seen in controls. While increasing numbers of CD8+ Vbeta8+ were present in the class I- grafts at 3 weeks, this increase was not statistically significant. Thus, expression of class I alloantigens on a kidney graft plays an important role in regulating the rate of accumulation of CD8+ T cells in rejecting kidney grafts. However, the TCR Vbeta repertoire of the CD8+ T cell infiltrate is largely determined by factors that are independent of normal class I expression on the graft.

H2-M3wt-restricted, Listeria monocytogenes-specific CD8 T cells recognize a novel, hydrophobic, protease-resistant, periodate-sensitive antigen

Mice infected with Listeria monocytogenes (LM) generate H2-M3wt-restricted CD8 effectors which recognize a heat-killed LM-associated antigen (HAA) presented by macrophages. To characterize HAA, we extracted a bioactive component from LM using SDS or NaOH. Extracted HAA aggregated in hydrophilic solvents but dissociated in the presence of SDS into a smaller subunit which migrated in Sephadex G-200 between chymotrypsinogen (25 kDa) and cytochrome c (12.5 kDa). HAA bioactivity and size was unaffected by proteinase K under conditions which degraded virtually all detectable protein. HAA was also unaffected by other proteases, RNase and DNase, but HAA bioactivity was destroyed by periodate, an agent that degrades carbohydrates. These studies demonstrate that H2-M3wt can present a hydrophobic, non-peptide, microbial antigen, probably glycolipid in origin, to CD8 T cells.

Bacterial DNA induces murine interferon-gamma production by stimulation of interleukin-12 and tumor necrosis factor-alpha

Bacterial, but not mammalian DNA, can induce interferon-gamma (IFN-gamma) in murine splenocytes. To elucidate the basis of this activity, we have assessed in vitro cytokine production by C3H/HeJ splenocytes stimulated with either DNA from Escherichia coli or a synthetic oligonucleotide containing an active palindromic sequence identified from DNA. Both DNAs induced IFN-gamma production, with the requirement for intact DNA shown by sensitivity to DNase digestion. Fractionated cell populations were evaluated to determine direct or indirect cellular effects of the DNA. Although bacterial DNA failed to induce IFN-gamma in the nonadherent cell population, supernatants from adherent cells stimulated by DNA induced IFN-gamma production by these cells. Interleukin-12 (IL-12) was detectable in supernatants from DNA-stimulated splenocytes before IFN-gamma, and neutralizing antibodies directed against IL-12 markedly inhibited the induction of IFN-gamma. Anti-tumor necrosis factor-alpha (TNF-alpha) antibodies also inhibited IFN-gamma production, and the combination of both anti-IL-12 and anti-TNF-alpha could totally inhibit production of IFN-gamma. Taken together, these results indicate that the stimulation of IFN-gamma production by bacterial DNA is mediated by IL-12 and TNF-alpha and point to macrophages/monocytes as targets of action of this macromolecule.

Analysis of the interrelationship between IL-12, TNF-alpha, and IFN-gamma production during murine listeriosis

IL-12, a recently described cytokine, is an important mediator in the early production of IFN-gamma during infection. To evaluate the timing of IL-12 production, and its relationship to TNF-alpha, and IFN-gamma production during primary murine listeriosis, we measured cytokine mRNA and protein levels in C57B1/6 mice infected intravenously with Listeria monocytogenes (LM). IL-12 is a disulfide-linked heterodimer containing two chains (designated P35 and P40); however, bioactive cytokine production has been more closely linked with P40 expression. Consequently, we monitored mRNA and protein levels of P40 in the spleen as a marker for IL-12 production in vivo. Splenic P40 mRNA levels (assayed using RNase protection methods) were low in uninfected animals, but increased markedly beginning 15 to 18 hr after LM infection. In sublethally infected animals, P40 mRNA levels remained elevated for 5 days, returning to baseline with the resolution of infection. P40 protein (assayed using an antibody capture ELISA) could be detected in the spleens of LM-infected animals beginning around 18 hr postinfection confirming linkage between P40 mRNA accumulation and the generation of a protein product. In comparing P40 and IFN-gamma mRNA levels in vivo, we found in each case that substantial increases in mRNA accumulation did not appear until 15-18 hr postinfection. In comparable studies using BALB/c animals, cytokine production began slightly earlier (between 12 and 15 hr) but once again P40 and IFN-gamma mRNA levels increased in a coordinated manner. P40 mRNA (like IFN-gamma and TNF-alpha mRNA) only accumulated in animals infused with live, virulent bacteria. Although we could detect no obvious lag between the time of onset of IL-12 and IFN-gamma accumulation in vivo, infusions of anti-IL-12 antibodies markedly reduced IFN-gamma expression implying that IL-12 production precedes and directs IFN-gamma production. TNF-alpha production, on the other hand, was not diminished by anti-IL-12 treatment. Our studies demonstrate that IL-12 generation is an essential step in normal IFN-gamma production during listeriosis, and suggest that IL-12, once produced, may begin enhancing IFN-gamma production in vivo in less than 3 hr.

Cytokine expression in vivo during murine listeriosis. Infection with live, virulent bacteria is required for monokine and lymphokine messenger RNA accumulation in the spleen

To examine the regulation of cytokine synthesis during murine listeriosis, we have monitored IFN-gamma, TNF-alpha, and IL-1 beta mRNA levels in the spleens of C57B1/6 mice after the i.v. infusion of virulent and nonvirulent preparations of Listeria monocytogenes (LM). Messenger RNA coding for TNF, IL-1, or IFN did not become detectable until approximately 12 to 15 h after the infusion of virulent LM. Levels of each cytokine mRNA then increased synchronously reaching peak or near peak levels around 24 h after infection. Levels gradually decreased over the next 4 to 5 days. Unlike virulent LM, neither heat-killed LM, nor nonvirulent LM variants lacking listeriolysin O, stimulated monokine or IFN mRNA accumulation even when administered in very large doses. To gain perspective concerning the response to LM, we examined the early pattern of cytokine mRNA accumulation induced by Salmonella typhimurium (ST), an intracellular pathogen expressing LPS. We noted at least three significant differences between the cytokine responses to LM and ST: 1) monokine mRNA levels increased much more rapidly (within 1 h) after ST infection; 2) unlike LM, ST retained the capacity to stimulate cytokine mRNA production when injected as heat-killed bacteria; 3) in contrast to LM, ST could not trigger the early IFN production characteristic of LM infection. Our data suggest that monokine and IFN production early in listeriosis are critically linked with the process of bacterial invasion of host cells. The timing and pattern of cytokine mRNA accumulation in this setting is qualitatively different from that induced by LPS. The pathway described in these studies may also play a role in the host cytokine response to other intracellular pathogens as well.

Cytokine expression in vivo during murine listeriosis. Infection with live, virulent bacteria is required for monokine and lymphokine messenger RNA accumulation in the spleen

To examine the regulation of cytokine synthesis during murine listeriosis, we have monitored IFN-gamma, TNF-alpha, and IL-1 beta mRNA levels in the spleens of C57B1/6 mice after the i.v. infusion of virulent and nonvirulent preparations of Listeria monocytogenes (LM). Messenger RNA coding for TNF, IL-1, or IFN did not become detectable until approximately 12 to 15 h after the infusion of virulent LM. Levels of each cytokine mRNA then increased synchronously reaching peak or near peak levels around 24 h after infection. Levels gradually decreased over the next 4 to 5 days. Unlike virulent LM, neither heat-killed LM, nor nonvirulent LM variants lacking listeriolysin O, stimulated monokine or IFN mRNA accumulation even when administered in very large doses. To gain perspective concerning the response to LM, we examined the early pattern of cytokine mRNA accumulation induced by Salmonella typhimurium (ST), an intracellular pathogen expressing LPS. We noted at least three significant differences between the cytokine responses to LM and ST: 1) monokine mRNA levels increased much more rapidly (within 1 h) after ST infection; 2) unlike LM, ST retained the capacity to stimulate cytokine mRNA production when injected as heat-killed bacteria; 3) in contrast to LM, ST could not trigger the early IFN production characteristic of LM infection. Our data suggest that monokine and IFN production early in listeriosis are critically linked with the process of bacterial invasion of host cells. The timing and pattern of cytokine mRNA accumulation in this setting is qualitatively different from that induced by LPS. The pathway described in these studies may also play a role in the host cytokine response to other intracellular pathogens as well.

Specialized role for a murine class I-b MHC molecule in prokaryotic host defenses

Although nonclassical (class I-b) gene products represent the majority of murine major histocompatibility complex (MHC) genes, the role of these relatively nonpolymorphic molecules remains uncertain. Recently, one such protein, H-2M3 (formerly designated Hmt), was shown to bind and specifically present N-formylated peptides to cytotoxic T lymphocytes. Because N-formylation is characteristic of prokaryotic proteins, this MHC molecule may be especially adapted for a role in the mammalian defense against bacterial attack. The current studies demonstrate that an MHC molecule, indistinguishable from H-2M3, presents antigens derived from the intracellular pathogen Listeria monocytogenes to Listeria-specific CD8+ cells.

Metabolic requirements for macrophage presentation of Listeria monocytogenes to immune CD8 cells

Though ingested Ag are readily degraded into peptides within endocytic vesicles, APC usually cannot present these fragments to CD8 cells. Despite this generalization, some exceptions have been noted. For example, murine macrophage targets readily process heat-killed Listeria monocytogenes (HKLM) into a form recognizable by immune CD8 CTL. Using an assay of Listeria-specific, CD8-mediated cytotoxicity to quantitate Ag presentation by C57Bl/6 macrophage targets, we have examined some of the cellular requirements for this form of Ag processing. To assess whether the physical form of the Ag is an important determinant of processing, we compared the ability of macrophages to present intact HKLM, fractionated L. monocytogenes (LM) membranes, and octyl-beta-d-thioglucopyranoside-solubilized extracts of LM membranes. Macrophages presented each Ag form in a similar manner indicating that processing is not critically dependent on the presence of intact bacteria or even on the introduction of Ag in a particulate form. To gain insight into the metabolic requirements for Ag processing, we examined the effects of several inhibitors. As might be expected, listerial Ag presentation was blocked by brefeldin, a known inhibitor of the endogenous pathway of Ag processing. LM Ag presentation, however, was also blocked by inhibitors of endosomal acidification (chloroquine, ammonium chloride, and monensin) and by the acid protease inhibitor pepstatin A, suggesting that endocytic processing may play an essential role in CD8 recognition of this Ag. To formally establish that this pattern of exogenous Ag processing requires the presence of a class I MHC product, we demonstrated that beta-2 microglobulin-deficient macrophages, which lack class I MHC product expression, cannot present HKLM to CD8 cells. However, we could not block Ag presentation by incubating macrophages with monoclonal anti-H-2K or H-2D antibodies, suggesting that LM Ag presentation may be mediated by some other class I MHC product. Additional characterization of this pathway of Ag presentation is warranted in view of its possible role in initiating CD8-mediated immunity against microbial Ag.

Metabolic requirements for macrophage presentation of Listeria monocytogenes to immune CD8 cells

Though ingested Ag are readily degraded into peptides within endocytic vesicles, APC usually cannot present these fragments to CD8 cells. Despite this generalization, some exceptions have been noted. For example, murine macrophage targets readily process heat-killed Listeria monocytogenes (HKLM) into a form recognizable by immune CD8 CTL. Using an assay of Listeria-specific, CD8-mediated cytotoxicity to quantitate Ag presentation by C57Bl/6 macrophage targets, we have examined some of the cellular requirements for this form of Ag processing. To assess whether the physical form of the Ag is an important determinant of processing, we compared the ability of macrophages to present intact HKLM, fractionated L. monocytogenes (LM) membranes, and octyl-beta-d-thioglucopyranoside-solubilized extracts of LM membranes. Macrophages presented each Ag form in a similar manner indicating that processing is not critically dependent on the presence of intact bacteria or even on the introduction of Ag in a particulate form. To gain insight into the metabolic requirements for Ag processing, we examined the effects of several inhibitors. As might be expected, listerial Ag presentation was blocked by brefeldin, a known inhibitor of the endogenous pathway of Ag processing. LM Ag presentation, however, was also blocked by inhibitors of endosomal acidification (chloroquine, ammonium chloride, and monensin) and by the acid protease inhibitor pepstatin A, suggesting that endocytic processing may play an essential role in CD8 recognition of this Ag. To formally establish that this pattern of exogenous Ag processing requires the presence of a class I MHC product, we demonstrated that beta-2 microglobulin-deficient macrophages, which lack class I MHC product expression, cannot present HKLM to CD8 cells. However, we could not block Ag presentation by incubating macrophages with monoclonal anti-H-2K or H-2D antibodies, suggesting that LM Ag presentation may be mediated by some other class I MHC product. Additional characterization of this pathway of Ag presentation is warranted in view of its possible role in initiating CD8-mediated immunity against microbial Ag.

Analysis of the time course of IFN-gamma mRNA and protein production during primary murine listeriosis. The immune phase of bacterial elimination is not temporally linked to IFN production in vivo

IFN-gamma clearly plays an important role in the murine host response against Listeria monocytogenes, but the time course of its production and its precise role in immunity remain controversial. To address these issues, we sequentially monitored IFN production and bacterial accumulation in vivo in C57B1/6 mice during primary listeriosis. IFN-gamma mRNA levels (measured by Northern blot analysis of freshly isolated splenic RNA) and serum IFN (measured by ELISA) were both maximal on day 1 of infection, decreasing steadily after day 2 to barely detectable levels by days 4 to 6. Significantly, there was no direct relationship between IFN levels and listericidal activity in vivo. Between days 1 and 3, the period of maximal IFN production, host bacterial load (assessed by quantitating live L. monocytogenes/spleen) increased approximately 10- to 50-fold. On the other hand, during the immune phase of infection (between days 5 and 7), a period when both IFN mRNA and protein were barely detectable, the host bacterial load decreased 1,000- to 10,000-fold. The paucity of IFN production in vivo during the immune phase was unexpected in light of previous reports demonstrating abundant in vitro lymphokine release by splenocytes isolated during the same time period. By direct comparisons of IFN production in vivo and in vitro, however, we could show that the late (days 6-7) peak of IFN release observed in Ag-stimulated cultures was an in vitro artifact. By contrast the pattern of spontaneous IFN release (obtained when freshly isolated cells were incubated in the absence of Ag) conformed more closely to that observed in vivo. Because listerial Ag stimulated vigorous lymphokine release in vitro, we sought to determine whether an analogous effect could be observed in vivo. In fact, even the infusion of very large doses of live bacteria (5-20,000,000/mouse) did not stimulate endogenous IFN-gamma production in mice infected for 6 to 7 days. These studies suggest three major conclusions: 1) IFN production in vivo occurs primarily during the early phase of listeriosis; 2) the dramatic decrease in bacterial numbers observed late in infection cannot be directly attributed to increased IFN production by LM-immune T cells; 3) although Ag-driven cultures of freshly isolated cells can provide useful information about the potential lymphokine-producing capabilities of Ag-specific T cells, these results have limited relevance in understanding patterns of T cell lymphokine production in vivo.

Analysis of the time course of IFN-gamma mRNA and protein production during primary murine listeriosis. The immune phase of bacterial elimination is not temporally linked to IFN production in vivo

IFN-gamma clearly plays an important role in the murine host response against Listeria monocytogenes, but the time course of its production and its precise role in immunity remain controversial. To address these issues, we sequentially monitored IFN production and bacterial accumulation in vivo in C57B1/6 mice during primary listeriosis. IFN-gamma mRNA levels (measured by Northern blot analysis of freshly isolated splenic RNA) and serum IFN (measured by ELISA) were both maximal on day 1 of infection, decreasing steadily after day 2 to barely detectable levels by days 4 to 6. Significantly, there was no direct relationship between IFN levels and listericidal activity in vivo. Between days 1 and 3, the period of maximal IFN production, host bacterial load (assessed by quantitating live L. monocytogenes/spleen) increased approximately 10- to 50-fold. On the other hand, during the immune phase of infection (between days 5 and 7), a period when both IFN mRNA and protein were barely detectable, the host bacterial load decreased 1,000- to 10,000-fold. The paucity of IFN production in vivo during the immune phase was unexpected in light of previous reports demonstrating abundant in vitro lymphokine release by splenocytes isolated during the same time period. By direct comparisons of IFN production in vivo and in vitro, however, we could show that the late (days 6-7) peak of IFN release observed in Ag-stimulated cultures was an in vitro artifact. By contrast the pattern of spontaneous IFN release (obtained when freshly isolated cells were incubated in the absence of Ag) conformed more closely to that observed in vivo. Because listerial Ag stimulated vigorous lymphokine release in vitro, we sought to determine whether an analogous effect could be observed in vivo. In fact, even the infusion of very large doses of live bacteria (5-20,000,000/mouse) did not stimulate endogenous IFN-gamma production in mice infected for 6 to 7 days. These studies suggest three major conclusions: 1) IFN production in vivo occurs primarily during the early phase of listeriosis; 2) the dramatic decrease in bacterial numbers observed late in infection cannot be directly attributed to increased IFN production by LM-immune T cells; 3) although Ag-driven cultures of freshly isolated cells can provide useful information about the potential lymphokine-producing capabilities of Ag-specific T cells, these results have limited relevance in understanding patterns of T cell lymphokine production in vivo.

MHC-unrestricted transfer of antilisterial immunity by freshly isolated immune CD8 spleen cells

Immune CD8 cells, which play an essential role in the adoptive transfer of antilisterial immunity, can specifically lyse Listeria-bearing macrophages in vitro in an MHC-unrestricted manner. In contrast, the adoptive transfer of immunity by unseparated immune lymphocytes has been reported to be MHC-restricted. To address the restriction properties of CD8 effectors in vivo, we assessed their efficacy in protecting syngeneic and allogeneic recipients. Protection was determined by comparing the number of viable splenic Listeria in naive mice and in recipients of 60 million CD8-enriched, L3T4-depleted, Listeria-immune spleen cells, 2 days after the infusion of 10,000 Listeria. Donor cells from B6 (H-2b) mice transferred about 4 logs of protection in syngeneic recipients and more than 2 logs in allogeneic B10.A (H-2a) or B10.BR (H-2k) mice. Immune B10.A CD8 cells transferred equivalent protection to B6 mice. Protection was almost completely abrogated by the lysis or lethal irradiation of CD8 cells before transfer in vivo. On the other hand, the depletion of macrophages or NK cells did not impair adoptive transfer. By comparison, nonimmune CD8 cells from normal mice or from mice stimulated with an irrelevant Ag in vivo did not transfer substantial immunity to allogeneic recipients. We have noted previously that protective CD8 cells inhibit phagocyte accumulation in the spleen of Listeria-infected syngeneic recipients. In the present studies, we observed similar changes in adoptively immunized allogeneic mice. Reduced phagocyte accumulation may reflect Listeria-dependent lysis of infected phagocytes by immune CD8 cells. In support of this, we showed that Listeria-immune donor cells rapidly acquired the capacity to mediate Listeria-dependent, MHC-unrestricted lysis of macrophages after incubation with small amounts of IL-2 in vitro. In sum, our data establish that Listeria-immune CD8 cells can function in vivo in MHC incompatible hosts, and indirectly support the hypothesis that the destruction of infected phagocytes may be important in T cell-mediated immunity against Listeria and perhaps other intracellular pathogens.

MHC-unrestricted transfer of antilisterial immunity by freshly isolated immune CD8 spleen cells

Immune CD8 cells, which play an essential role in the adoptive transfer of antilisterial immunity, can specifically lyse Listeria-bearing macrophages in vitro in an MHC-unrestricted manner. In contrast, the adoptive transfer of immunity by unseparated immune lymphocytes has been reported to be MHC-restricted. To address the restriction properties of CD8 effectors in vivo, we assessed their efficacy in protecting syngeneic and allogeneic recipients. Protection was determined by comparing the number of viable splenic Listeria in naive mice and in recipients of 60 million CD8-enriched, L3T4-depleted, Listeria-immune spleen cells, 2 days after the infusion of 10,000 Listeria. Donor cells from B6 (H-2b) mice transferred about 4 logs of protection in syngeneic recipients and more than 2 logs in allogeneic B10.A (H-2a) or B10.BR (H-2k) mice. Immune B10.A CD8 cells transferred equivalent protection to B6 mice. Protection was almost completely abrogated by the lysis or lethal irradiation of CD8 cells before transfer in vivo. On the other hand, the depletion of macrophages or NK cells did not impair adoptive transfer. By comparison, nonimmune CD8 cells from normal mice or from mice stimulated with an irrelevant Ag in vivo did not transfer substantial immunity to allogeneic recipients. We have noted previously that protective CD8 cells inhibit phagocyte accumulation in the spleen of Listeria-infected syngeneic recipients. In the present studies, we observed similar changes in adoptively immunized allogeneic mice. Reduced phagocyte accumulation may reflect Listeria-dependent lysis of infected phagocytes by immune CD8 cells. In support of this, we showed that Listeria-immune donor cells rapidly acquired the capacity to mediate Listeria-dependent, MHC-unrestricted lysis of macrophages after incubation with small amounts of IL-2 in vitro. In sum, our data establish that Listeria-immune CD8 cells can function in vivo in MHC incompatible hosts, and indirectly support the hypothesis that the destruction of infected phagocytes may be important in T cell-mediated immunity against Listeria and perhaps other intracellular pathogens.

Genetic control of inflammatory arthritis in congenic lpr mice

To determine the genetic requirements for the development of inflammatory arthritis in MRL-lpr/lpr mice, clinical, serologic, and pathologic features of lpr/lpr and +/+ mice of MRL, B6, C3H, and AKR strains were studied. Arthritis was evaluated by histopathologic examination of the knee joint, while sera were tested for the presence of rheumatoid factor (RF) and anti-DNA activity by ELISA. Of the strains tested to age 7 months, only the MRL-lpr/lpr mice developed histologic evidence of arthritis. All lpr mice, however, produced both IgM RF and IgG RF, although amounts varied among strains. These results indicate that the lpr gene as well as another gene(s) in the MRL background are necessary for the development of inflammatory arthritis and that this lesion may be independent of RF production.

Comparison of the effects of IL-1 alpha and TNF-alpha on phagocyte accumulation and murine antibacterial immunity

IL-1 and TNF both are reported to increase host antibacterial resistance. To directly compare their effects on tissue phagocyte accumulation and antibacterial activity, we infused recombinant human IL-1 alpha and TNF-alpha into C3H/HeJ mice. Although IL-1, at a dose of 1 microgram/day, did not significantly elevate blood neutrophil concentrations, it increased the number of PMNs within the spleen three to fourfold within 2 days. Similar neutrophil accumulation also occurred in the lungs, bone marrow, and liver of treated animals without detectable changes in macrophage numbers. IL-1 also increased myelopoiesis in the spleen by Days 3-4 of infusions. The capacity of splenocytes from IL-1-treated animals to kill Listeria monocytogenes in vitro and to suppress listeria proliferation in vivo after the intravenous infusion of bacteria both rose in parallel with PMN accumulation. Comparable doses of TNF also enhanced listeria killing in vivo but in contrast to IL-1, it significantly depressed peripheral blood neutrophil counts, and inhibited splenic neutrophil accumulation and in vitro listericidal activity in listeria-infected mice. Our results suggest that IL-1 enhances host resistance to infection by increasing tissue neutrophil accumulation while TNF protects by a different mechanism, despite a net inhibitory effect on neutrophil accumulation.

Characterization of the pattern of inflammatory cell influx and cytokine production during the murine host response to Listeria monocytogenes

To examine the physiologic mechanisms responsible for enhanced antibacterial activity during infection with Listeria monocytogenes (LM), we developed an in vitro assay for quantifying leukocyte anti-listerial activity (LAA) in spleen and bone marrow. When LAA was serially measured in C57B1/6 (B6) mice infected i.v. with LM, two distinct phases of response were observed. Splenic LAA increased four- to fivefold during the first 2 days after i.v. infusion of LM (from 2.4 +/- 1.8 U/spleen before infection to 11.8 +/- 2.4, p less than 0.01), dropped significantly on days 3 to 4, and increased again to similar levels from days 5 to 7. A fall in bone marrow activity from the 3.5 +/- 1.5 to 1.6 +/- 0.7 U/mouse (two femurs) coincided with the initial rise in splenocyte activity, and was followed by a gradual return to base line. Bacterial containment in vivo correlated well with splenic LAA in vitro. Carbonyl iron pretreatment of cells from both normal and LM-infected animals ablated LAA, suggesting the effectors were phagocytic. LAA in normal spleens was unaffected by 400 rad; LAA of normal marrow as well as splenocyte and marrow cell suspensions obtained 2 days after LM infection was markedly reduced by this dose of irradiation. Quantitative studies of spleen composition revealed a 10-fold increase in polymorphonuclear neutrophils between day 0 and day 2 followed by a marked decrease on day 3; this pattern closely resembled the changes in LAA observed during the same period. In contrast, splenic macrophage number did not increase from base line until after day 3. To look for evidence of changes in the efficiency of bacterial killing by phagocytes during infection, we calculated LAA/splenic phagocyte. The efficiency of killing increased threefold over base line within 1 day after LM infusion but we detected no additional increases later in infection. Because cytokines may have mediated some or all of the changes observed, we measured the capacity of splenocytes obtained at various times after infection to produce IL-2, TNF, and IFN-gamma in vitro. TNF activity increased in parallel with the first and second LAA peaks, whereas increases in IL-2 and IFN-gamma activity were associated only with the second.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of the pattern of inflammatory cell influx and cytokine production during the murine host response to Listeria monocytogenes

To examine the physiologic mechanisms responsible for enhanced antibacterial activity during infection with Listeria monocytogenes (LM), we developed an in vitro assay for quantifying leukocyte anti-listerial activity (LAA) in spleen and bone marrow. When LAA was serially measured in C57B1/6 (B6) mice infected i.v. with LM, two distinct phases of response were observed. Splenic LAA increased four- to fivefold during the first 2 days after i.v. infusion of LM (from 2.4 +/- 1.8 U/spleen before infection to 11.8 +/- 2.4, p less than 0.01), dropped significantly on days 3 to 4, and increased again to similar levels from days 5 to 7. A fall in bone marrow activity from the 3.5 +/- 1.5 to 1.6 +/- 0.7 U/mouse (two femurs) coincided with the initial rise in splenocyte activity, and was followed by a gradual return to base line. Bacterial containment in vivo correlated well with splenic LAA in vitro. Carbonyl iron pretreatment of cells from both normal and LM-infected animals ablated LAA, suggesting the effectors were phagocytic. LAA in normal spleens was unaffected by 400 rad; LAA of normal marrow as well as splenocyte and marrow cell suspensions obtained 2 days after LM infection was markedly reduced by this dose of irradiation. Quantitative studies of spleen composition revealed a 10-fold increase in polymorphonuclear neutrophils between day 0 and day 2 followed by a marked decrease on day 3; this pattern closely resembled the changes in LAA observed during the same period. In contrast, splenic macrophage number did not increase from base line until after day 3. To look for evidence of changes in the efficiency of bacterial killing by phagocytes during infection, we calculated LAA/splenic phagocyte. The efficiency of killing increased threefold over base line within 1 day after LM infusion but we detected no additional increases later in infection. Because cytokines may have mediated some or all of the changes observed, we measured the capacity of splenocytes obtained at various times after infection to produce IL-2, TNF, and IFN-gamma in vitro. TNF activity increased in parallel with the first and second LAA peaks, whereas increases in IL-2 and IFN-gamma activity were associated only with the second.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of an anti-I-Ab antibody on murine host resistance to Listeria monocytogenes

Infection with Listeria monocytogenes stimulates T cell proliferation and T cell-derived lymphokine production. The release of lymphokines, in turn, "activates" macrophages, enhancing their bactericidal capacity. Because prior studies suggest that I-A+ accessory cells play a critical role in this pathway, we assessed the effects of an anti-I-A antibody on the murine host resistance to listerial infection. To this end, we infused Listeria into control C57BL/6 mice (I-Ab haplotype) and mice of the same strain which had been pretreated 18 hr earlier with D3137 (a monoclonal IgG2a anti-I-Ab,d antibody). Preliminary studies demonstrated that this antibody can markedly inhibit antigen-induced proliferation of Listeria-dependent T cells in vitro and (at a dose of 1 mg/animal) can markedly reduce I-A expression on splenocytes in vivo. Even though D3137 pretreatment prevented the splenomegaly normally observed after Listeria infusion into mice, it protected animals infused with otherwise lethal concentrations of Listeria. Because antibody-treated animals had sevenfold fewer organisms in their spleens 18 hr after infection and 1000-fold fewer organisms than control animals 3 days after infection, improved survival resulted from an antibody-induced increase in the bactericidal capacity of the MPS. Protection was not noted when C1.18.4 (an IgG2a myeloma protein without known antibody activity) was infused into C57BL/6 mice or when D3137 was infused in B10.BR (I-Ak) mice. D3137 also protected (B10 X B10.BR)F1 mice (which are hybrids bearing I-Ab and I-Ak), suggesting that complete blockade of antigen presentation is not a prerequisite for its protective action. Further studies into the mechanism for these effects may provide new insights into the pathophysiology of MPS activation in response to immunologic challenge.

The effects of an anti-I-Ab antibody on murine host resistance to Listeria monocytogenes

Infection with Listeria monocytogenes stimulates T cell proliferation and T cell-derived lymphokine production. The release of lymphokines, in turn, "activates" macrophages, enhancing their bactericidal capacity. Because prior studies suggest that I-A+ accessory cells play a critical role in this pathway, we assessed the effects of an anti-I-A antibody on the murine host resistance to listerial infection. To this end, we infused Listeria into control C57BL/6 mice (I-Ab haplotype) and mice of the same strain which had been pretreated 18 hr earlier with D3137 (a monoclonal IgG2a anti-I-Ab,d antibody). Preliminary studies demonstrated that this antibody can markedly inhibit antigen-induced proliferation of Listeria-dependent T cells in vitro and (at a dose of 1 mg/animal) can markedly reduce I-A expression on splenocytes in vivo. Even though D3137 pretreatment prevented the splenomegaly normally observed after Listeria infusion into mice, it protected animals infused with otherwise lethal concentrations of Listeria. Because antibody-treated animals had sevenfold fewer organisms in their spleens 18 hr after infection and 1000-fold fewer organisms than control animals 3 days after infection, improved survival resulted from an antibody-induced increase in the bactericidal capacity of the MPS. Protection was not noted when C1.18.4 (an IgG2a myeloma protein without known antibody activity) was infused into C57BL/6 mice or when D3137 was infused in B10.BR (I-Ak) mice. D3137 also protected (B10 X B10.BR)F1 mice (which are hybrids bearing I-Ab and I-Ak), suggesting that complete blockade of antigen presentation is not a prerequisite for its protective action. Further studies into the mechanism for these effects may provide new insights into the pathophysiology of MPS activation in response to immunologic challenge.

Comparison of intravenous gamma globulin and a monoclonal anti-Fc receptor antibody as inhibitors of immune clearance in vivo in mice

Fc-receptor-mediated clearance and nonspecific phagocytic clearance were assessed after the infusion of monomeric human IgG, heat-aggregated human IgG, and a monoclonal anti-mouse macrophage FcII receptor antibody (2.4G2) into normal mice. Each agent blocked Fc-receptor function in vivo, but 2.4G2 was much more potent per microgram than the other agents. Monomeric IgG in blocking doses did not affect other aspects of immune function. In contrast, aggregated IgG, and to a lesser extent, 2.4G2 reduced serum complement levels. In addition, these agents also caused moderate reductions in nonspecific phagocytic function. Monoclonal anti-mouse macrophage C3bi receptor antibody (Mac-1), another monoclonal antibody which binds to macrophage CR3 receptors without interfering with Fc-receptor function, also reduced serum complement and inhibited nonspecific phagocytic function. Complement depletion alone (produced by infusion of cobra venom factor) could not account for the observed changes in Fc receptor or nonspecific phagocytic function. We conclude that both monomeric IgG and anti-Fc-receptor antibodies can markedly inhibit Fc-receptor function in vivo; however, the pattern of physiologic changes produced by these agents differs.

The clearance of a monoclonal anti-DNA antibody following administration of DNA in normal and autoimmune mice

To study the assembly of DNA-anti-DNA complexes in vivo, we have measured the clearance from blood and organ localization of a murine IgG2a monoclonal anti-DNA antibody, called 6/0, following the infusion of DNA intravenously or intraperitoneally. Intraperitoneal DNA caused a profound acceleration of 6/0 anti-DNA clearance that was dose dependent and demonstrable after the infusion of as little as 1.9 microgram per gram of body weight of single-stranded DNA. The antibody was cleared primarily in the liver without increased deposition in the kidney. Intraperitoneal infusions of DNA also accelerated the clearance of 6/0 in autoimmune MRL-lpr/lpr mice. In contrast, intravenous DNA given in comparable doses caused only a slight increase in 6/0 antibody clearance; this accelerated clearance was seen only at low antigen doses and only during the first 10 min following DNA infusion. Using double-radiolabeling techniques, 6/0 and Cl.18, an IgG2ak myeloma protein without anti-DNA activity, were found to disappear from blood at a comparable rate in both B6D2 mice and MRL-lpr/lpr mice. These results suggest that the DNA-anti-DNA immune complexes can form in vivo but that this process is profoundly affected by the manner in which DNA enters the circulation. In addition, the results suggest that DNA-dependent clearance is not a major pathway for anti-DNA metabolism in normal or at least one strain of autoimmune mice.

Defects in mononuclear phagocytic system (MPS) function in autoimmune MRL-lpr/lpr mice

MRL-lpr/lpr mice develop an autoimmune disease similar to systemic lupus erythematosus. To determine whether mice of this strain develop defects in mononuclear phagocyte system (MPS) function similar to those observed in patients, the pattern of sequestration of labeled immune complexes was compared 90 min after infusion into MRL-lpr/lpr and into normal B6D2 mice. The amount of complexes persisting in the blood was increased, and the amount sequestered in the liver was significantly reduced in MRL-lpr/lpr mice in comparison to normal B6D2 controls. This defect was most evident in MRL-lpr/lpr mice of the ages of 25-26 weeks; mice of this age also demonstrated the greatest elevation of anti-DNA antibody levels. The role of the MRL strain background and of the lpr gene in determining this defect was investigated by analysis of MRL-+/-/+/- and of other lpr congenic strains (B6-lpr/lpr, AKR-lpr/lpr, and C3H-lpr/lpr). Both MRL-+/-/+/- and congenic lpr animals showed similar defects, although to a lesser degree than MRL-lpr/lpr mice. In contrast, MRL-lpr/lpr mice demonstrated normal clearance of heat-damaged red blood cells and heat-aggregated albumin. Thus MRL-lpr/lpr mice display a selective defect in MPS Fc receptor function and may provide a valuable model for elucidating the etiology and importance of MPS dysfunction in immune complex deposition disease.

The blockade of Fc receptor-mediated clearance of immune complexes in vivo by a monoclonal antibody (2.4G2) directed against Fc receptors on murine leukocytes

To evaluate the feasibility of using a monoclonal anti-Fc receptor antibody to alter Fc receptor function in vivo, the disappearance of radiolabeled human serum albumin-rabbit anti-human serum albumin (HSA-anti-HSA) complexes was studied in mice before and after the infusion of 2.4G2, a monoclonal antibody (developed by J. Unkeless). 2.4G2 specifically binds to Fc receptors on mouse macrophages. Under standardized conditions, 6.1% of an i.v. administered dose of anti-HSA was sequestered in the liver of B6/D2J mice. When HSA-anti-HSA complexes were administered, 53.4% were sequestered. If 8 micrograms/g body weight of 2.4G2 was infused i.p. 1.5 hr before HSA-anti-HSA, only 13.7% of the infused complexes were sequestered in the liver. The inhibition in Fc receptor-mediated sequestration produced by this dose of antibody persisted for at least 24 hr. A dose of 1 to 2 micrograms/g was sufficient to inhibit sequestration by 50%. Animals receiving daily injections of 2.4G2 cleared immune complexes from their blood much more slowly than untreated animals. Because 2.4G2 was not cytotoxic to peritoneal macrophages in vitro in the presence of serum, and because comparable inhibition of Fc receptor function was observed in vivo in C5-deficient mice, blockade of function does not depend upon complement-mediated lysis of macrophages. The maximal degree of inhibition of Fc receptor function obtained by using intact 2.4G2 was about twice that observed by using Fab fragments of 2.4G2 to block receptors. In addition to its effect on Fc receptor function, 2.4G2 also had a small but significant inhibitory effect upon the clearance of 125I-labeled heat-aggregated HSA by the mononuclear phagocyte system both in intact and C5-deficient mice. We conclude that 2.4G2 is a potent inhibitor of IgG Fc receptor-mediated immune clearance in vivo.

The blockade of Fc receptor-mediated clearance of immune complexes in vivo by a monoclonal antibody (2.4G2) directed against Fc receptors on murine leukocytes

To evaluate the feasibility of using a monoclonal anti-Fc receptor antibody to alter Fc receptor function in vivo, the disappearance of radiolabeled human serum albumin-rabbit anti-human serum albumin (HSA-anti-HSA) complexes was studied in mice before and after the infusion of 2.4G2, a monoclonal antibody (developed by J. Unkeless). 2.4G2 specifically binds to Fc receptors on mouse macrophages. Under standardized conditions, 6.1% of an i.v. administered dose of anti-HSA was sequestered in the liver of B6/D2J mice. When HSA-anti-HSA complexes were administered, 53.4% were sequestered. If 8 micrograms/g body weight of 2.4G2 was infused i.p. 1.5 hr before HSA-anti-HSA, only 13.7% of the infused complexes were sequestered in the liver. The inhibition in Fc receptor-mediated sequestration produced by this dose of antibody persisted for at least 24 hr. A dose of 1 to 2 micrograms/g was sufficient to inhibit sequestration by 50%. Animals receiving daily injections of 2.4G2 cleared immune complexes from their blood much more slowly than untreated animals. Because 2.4G2 was not cytotoxic to peritoneal macrophages in vitro in the presence of serum, and because comparable inhibition of Fc receptor function was observed in vivo in C5-deficient mice, blockade of function does not depend upon complement-mediated lysis of macrophages. The maximal degree of inhibition of Fc receptor function obtained by using intact 2.4G2 was about twice that observed by using Fab fragments of 2.4G2 to block receptors. In addition to its effect on Fc receptor function, 2.4G2 also had a small but significant inhibitory effect upon the clearance of 125I-labeled heat-aggregated HSA by the mononuclear phagocyte system both in intact and C5-deficient mice. We conclude that 2.4G2 is a potent inhibitor of IgG Fc receptor-mediated immune clearance in vivo.

Human peritoneal macrophages possess two populations of IgG Fc receptors

To characterize the binding properties of the Fc receptors on human macrophages, the binding of radiolabeled human IgG1 to peritoneal macrophages was assessed. Cells were obtained at the time of diagnostic laparoscopy from women undergoing evaluation of infertility. Macrophages bound on the average more IgG1 monomer than monocytes but the avidity with which both types of cells bound IgG1 monomer was comparable. By contrast, macrophages bound much more IgG1 dimers than monocytes. Scatchard plots of the binding of dimer to monocytes were linear, but plots of binding to macrophages were markedly curvilinear. This curvilinearity was not an artifact of extensive ligand internalization or catabolism by cells, since 80% of binding was reversible and there was very little catabolism of ligand in the medium. Assuming that the observed curvilinearity was due to the presence of two independent subpopulations of receptors, an objective estimate for the number of receptors per cell and of the avidity with which each subpopulation bound IgG1 dimer was obtained using a previously described computer program (Scatfit). The analysis of the binding of dimer to macrophages from six donors suggested the presence of 42,000 +/- 33,000 high avidity receptors per cell which bind IgG1 dimer with a mean Ka of 2.7 X 10(9) M-1 and 218,000 +/- 127,000 low avidity receptors which bind the same ligand with a Ka of 1.1 X 10(7) M-1. ADCC of IgG antibody-coated sheep red blood cells mediated by macrophages was less readily inhibited by soluble IgG1 monomer than ADCC mediated by peripheral blood monocytes. This provides further evidence for the presence of low avidity receptors which bind monomeric IgG1 poorly and also suggests that these sites are functionally active in triggering antibody-dependent immune clearance.

The binding and processing of monoclonal human IgG1 by cells of a human macrophage-like cell line (U937)

The goal of these experiments was to assess the relationship between the binding and processing of IgG by Fc-receptor-bearing cells. Cells of the U937 human macrophage-like cell line were incubated with 125I-labeled monomers, dimers, oligomers (composed of 2-4 IgG1 subunits), and HP (heavy polymers composed of 5 or more subunits per polymer) of monoclonal human IgG1 in vitro. Binding was assessed by spinning cells through a layer of phthalate oils. Internalization of IgG1 was assessed by quantitating residual binding to cells after surface-bound IgG was removed by a brief treatment with a solution containing 0.25 M acetic acid and 0.5 M sodium chloride. Catabolism was assessed by measuring the release of radioactive fragments of IgG1, which were not precipitated by 10% trichloroacetic acid. Unstimulated U937 bound about 10,000 molecules per cell of IgG1 monomer, with an equilibrium binding constant (Ka) of 5 X 10(8) M-1. After stimulation with a conditioned medium in vitro, binding per cell was increased 3-7--fold, and the Ka was decreased 2-4--fold. Both unstimulated and stimulated cells internalized and catabolized labeled IgG1 HP, but stimulated cells internalized and digested much more IgG1 HP per cell than unstimulated cells. Both monomers and dimers of IgG1 were internalized and degraded very slowly by stimulated cells, even though both preparations readily bound to cells. In contrast, oligomers and (to an even greater extent) IgG1 HP were internalized and degraded much more rapidly. Internalization of IgG1 HP was markedly inhibited by incubation at 4 degrees C, but not by incubation with a variety of metabolic inhibitors. Catabolism was inhibited by chloroquine and monensin (inhibitors of lysosomal acidification) and by cytochalasin (an inhibitor of microfilament polymerization). Binding to the surface of cells was not markedly inhibited by any agent tested. The capacity of cells to bind labeled IgG1 was markedly reduced by prior incubation in the presence of unlabeled IgG1. This reduction was in part due to the steric blockade of receptors caused by the avid, but reversible, binding of IgG1. In addition, IgG1 oligomers or HP (but not IgG1 monomers or dimers) also caused an irreversible reduction in the number of Fc receptors by a process analogous to receptor down-regulation, as observed in other receptor--ligand systems.

Blockade of Fc receptor-mediated binding to U-937 cells by murine monoclonal antibodies directed against a variety of surface antigens

The effect of murine IgG hybridoma antibodies directed against leukocyte antigens on the Fc receptor function of human cells was studied. For this purpose, the specific binding of 125I-labeled monomeric human IgG1 to a macrophage-like cell-line (U-937) was quantitated before and after incubation in the presence of murine monoclonal hybridoma antibodies. Four monoclonal hybridoma antibodies (A1G3, 23D6, 4F2, and 3A 10), each of which binds to different antigens on the surface of U-937 cells, rapidly and potently inhibited the specific binding of labeled IgG1 to these cells. Inasmuch as inhibition was mediated only by IgG antibodies with an intact Fc fragment and antibody activity against surface antigens found on U-937, inhibition appears to have resulted from the formation of a three-component complex composed of antibody bound by its Fab portion to antigen and by its Fc fragment to a Fc receptor. Equilibrium binding studies performed on treated cells confirmed that reduced Fc receptor-mediated binding was due to a reduction in the number of available receptors. Binding studies employing double isotope labeling methods demonstrated that about 0.5 to 1.0 Fc receptor was blocked for each molecule of intact antibody bound to a U-937 cell. Using several techniques, it was shown that most of the monoclonal antibody bound to cells and the Fc receptors blocked by antibody remained on the cell surface despite incubation at 37 degrees C for 3 hr. Thus, the loss of receptor function observed in these experiments was almost exclusively due to reversible receptor blockade rather than receptor internalization or degradation. The antibodies identified in these studies also markedly inhibited Fc receptors on one other human cell line (HL-60) as well as those on normal human peripheral blood monocytes.

Blockade of Fc receptor-mediated binding to U-937 cells by murine monoclonal antibodies directed against a variety of surface antigens

The effect of murine IgG hybridoma antibodies directed against leukocyte antigens on the Fc receptor function of human cells was studied. For this purpose, the specific binding of 125I-labeled monomeric human IgG1 to a macrophage-like cell-line (U-937) was quantitated before and after incubation in the presence of murine monoclonal hybridoma antibodies. Four monoclonal hybridoma antibodies (A1G3, 23D6, 4F2, and 3A 10), each of which binds to different antigens on the surface of U-937 cells, rapidly and potently inhibited the specific binding of labeled IgG1 to these cells. Inasmuch as inhibition was mediated only by IgG antibodies with an intact Fc fragment and antibody activity against surface antigens found on U-937, inhibition appears to have resulted from the formation of a three-component complex composed of antibody bound by its Fab portion to antigen and by its Fc fragment to a Fc receptor. Equilibrium binding studies performed on treated cells confirmed that reduced Fc receptor-mediated binding was due to a reduction in the number of available receptors. Binding studies employing double isotope labeling methods demonstrated that about 0.5 to 1.0 Fc receptor was blocked for each molecule of intact antibody bound to a U-937 cell. Using several techniques, it was shown that most of the monoclonal antibody bound to cells and the Fc receptors blocked by antibody remained on the cell surface despite incubation at 37 degrees C for 3 hr. Thus, the loss of receptor function observed in these experiments was almost exclusively due to reversible receptor blockade rather than receptor internalization or degradation. The antibodies identified in these studies also markedly inhibited Fc receptors on one other human cell line (HL-60) as well as those on normal human peripheral blood monocytes.

Characterization of the IgG-Fc receptor on human platelets

To determine quantitatively the number and avidity of receptors for the Fc portion of IgG on human platelets, we have measured the binding to platelets of human monomeric monoclonal IgG, and of small covalently crosslinked polymers of IgG1 labeled with 125I. The binding of labeled IgG1 monomers to platelets is too weak to permit quantitation. The binding of dimers or larger polymers of IgG1 is much more avid (greater at 4 degrees C than 37 degrees C), is readily reversible, and is saturable. The number of receptor sites ranges from 400 to 2000 per platelet and the mean equilibrium association constant (Ka) for the binding of dimers at 4 degrees C is 2.2 x 10(7) M-1 +/- 0.9 x 10(7) M-1. The binding is specific for the Fc portion of IgG, and IgG1 and IgG3 bind to the receptors much more avidly than IgG2 or IgG4. Unlabeled IgG1 dimers are about 7--8-fold more potent in inhibiting binding than are IgG1 monomers, and larger polymers are even more potent than dimers. Thus, the Fc receptors on platelets bind human IgG1 with the same specificity and similar avidity as Fc receptors on polymorphonuclear leukocytes (PMNs), but PMNs have about 300-fold more receptors per unit of surface area than platelets.

The binding of human immunoglobulin G1 monomer and small, covalently cross-linked polymers of immunoglobulin G1 to human peripheral blood monocytes and polymorphonuclear leukocytes

Covalently cross-linked dimers and oligomers composed of 2-4 subunits of monoclonal human IgG1 were prepared by incubation of purified monomeric IgG1 with glutaraldehyde followed by gelfiltration chromatography. Monomers, dimers, and oligomers then were labeled with (125)I and used to compare the binding properties of IgG Fc receptors on human peripheral blood monocytes and polymorphonuclear leukocytes (PMN). Binding of IgG1 to monocytes at 37 degrees C and of IgG1 polymers to PMN at 4 degrees C could be readily measured and were found to be reversible and saturable. Scatchard plots of binding were linear in each instance. Monocytes bound a mean of 20,200+/-6,800 molecules/cell of IgG1 monomer at saturation and comparable amounts of dimer or oligomer. The mean association constant (Ka) for binding of IgG1 monomer to monocytes was 8.6 x 10(8)M(-1) and the Ka for binding of dimer and oligomer were three-to fivefold greater.In contrast, PMN bound a mean of 460,000+/-130,000 molecules of IgG1 dimer at saturation and comparable amounts of oligomer. The Ka of binding in both cases was 100-1,000-fold lower than the Ka for binding of the same preparations to monocytes. Binding of labeled IgG1 to both cell types was more potently inhibited by unlabeled IgG1 and IgG3 than by IgG4 or IgG2. Binding of labeled polymers of IgG1 to monocytes was 10-100-fold more easily inhibited by monomeric IgG1 than was binding to PMN. Thus, there are significant quantitative and qualitative differences between the binding properties of Fc receptors present on monocytes and PMN.

Reversible and irreversible loss of Fc receptor function of human monocytes as a consequence of interaction with immunoglobulin G

The effects of IgG in different configurations on the Fc receptor function of human monocytes were studied. Receptor function was assessed by quantitating immune adherence and/or ingestion of human erythrocytes coated with IgG anti-D antibody. Monomeric IgGl in solution inhibited the Fc receptor function of monocytes, but this function was restored completely after washing. In contrast, monomeric IgG that was adsorbed nonspecifically to a plastic surface inhibited the Fc receptor function of monocytes even after washing away unbound IgGl. This loss of function could be blocked by sodium azide and was reversed when the IgG adsorbed to plastic was degraded by trypsin, suggesting that loss of function was the reversible consequence of localized binding of most of the monocyte's receptors at the point of contact with immobilized IgGl. Fluid-phase aggregates of IgGl also reduced the Fc receptor function of monocytes as a consequence of direct binding to the monocyte surface. High concentrations of purified aggregates rapidly reduced Fc receptor function but function was reversed by trypsin even after incubation for 18 h. Lower concentrations of aggregates reduced Fc receptor function more slowly, but after 18 h of incubation, lost function was not restored by trypsin treatment. Because the transition from reversible to irreversible loss was blocked by sodium azide, an energy-dependent process of ingestion, shedding or denaturation of receptors is responsible for this irreversible loss of Fc receptor function. Rabbit IgG anti-human IgG bound to IgG adsorbed to the surface of monocytes also mediated a loss of Fc receptor function as a result of the binding of Fc receptors to the Fc portion of the rabbit IgG molecule, a process analogous to the binding of aggregated IgG. After irreversible depletion of Fc receptor function by anti-IgG, partial recovery of function was detectable within 12-24 h of incubation in vitro, and this recovery was blocked by cycloheximide, suggesting that new receptor synthesis was required for restoration of function.

Quantitative evaluation of antibody-dependent lymphocyte-mediated lysis of human red cells

The ability of lymphocytes to lyse human red cells coated with anti-D antibody was assessed by measuring 51 Cr release from labeled red cells incubated with peripheral blood leukocyte suspensions from 12 normal donors. Mixed mononuclear cell suspensions (containing monocytes and lymphocytes) from all donors produced lysis of sensitized red cells. Treatment with carbonyl iron reduced monocyte concentration to less than 1.2% in all donors, as measured by morphologic criteria, esterase staining and ingestion of latex particles. Lysis of red cells following monocyte depletion was markedly reduced in 8 of the 12 donors. Despite depletion of monocytes, unchanged or increased lysis was noticed with the leukocytes of the remaining 4 donors. This lysis was due to lymphocytes, not to residual monocytes. If target red cells were treated with papain or trypsin prior to sensitization, marked lysis occurred with lymphocytes of all donors, including those which did not lyse unmodified red cells. Direct cytolysis of sensitized red cells during contact with small lymphocytes was recorded using microcinematography, which confirmed the role of lymphocytes in mediating lysis. Lymphocyte-mediated lysis of red cells increased with mounting levels of antibody sensitization regardless to prior treatment with papain. Papain increased antibody coating per red cell, yet lysis per molecule of antibody bound was also increased. Lysis was inhibited by IgG1 and IgG3 in the fluid phase but not by IgG2 or IgG4. At an equivalent level of antibody sensitization lysis was augmented by concurrent coating of the red cells with C3b, C3d and/or C4b, though these components could not produce lysis in the absence of antibody coating.

Lymphocyte-mediated lysis of antibody coated human red cells in the presence of human serum

When peripheral blood lymphocytes and human red cells coated with IgG were incubated in vitro in culture medium, antibody-dependent lymphocyte-mediated lysis was observed. This lysis was markedly inhibited by the addition of purified monoclonal IgG1 (1000 microgram/ml) to the culture medium. In contrast, lysis by lymphocytes of sensitized red cells in the presence of undiluted human serum was equal to or greater than lysis in medium alone, even in the presence of IgG1 at 1000 microgram/ml, despite the high concentration of IgG in human serum (6000--19,000 microgram/ml). Serum heated to 56 degrees C for 30 min also restored lysis in the presence of IgG1. When serum was separated into three fractions by passage through a Sephadex G-200 column, the third fraction, which contained proteins with a molecular weight of less than 100,000 d (but neither of the other two fractions nor purified human albumin), restored lymphocyte-mediated lysis in the presence of IgG1.

Quantitative influence of antibody and complement coating of red cells on monocyte-mediated cell lysis

Monocyte-mediated lysis in vitro of human red cells coated with measured amounts of immunoglobulin G (IgG) or complement were studied. 1,000-1,500 molecules of IgG anti-D are necessary to effect measurable lysis, and lysis increases linearly with increasing levels of antibody sensitization. 100 microgram/ml of IgG1 abolished lysis even at maximal levels of anti-D sensitization (15,000 molecules/cell). Two isoimmune IgG anti-A or anti-B antisera were 5 to 10-fold less efficient in promoting phagocytosis or lysis per molecule of IgG bound; however, because of the greater antigen density of A or B, more than 100,000 molecules IgG/cell could be bound, producing equivalent lysis to anti-D-coated cells. Although inhibition by IgG1 was similar at equivalent levels of sensitization with anti-A, anti-B, or anti-D at high levels of coating with anti-A or anti-B (not attainable with anti-D), lysis was not inhibited by IgG1. Cells coated with human complement components alone were not lysed by monocytes; however, complement coating augmented IgG-mediated lysis and reduced the quantity of anti-D necessary to produce lysis to less than 1,000 molecules/cell. After thorough degradation of C3b by serum to C3d, complement augmentation persisted.