Lysozyme synthesis by established human and murine histiocytic lymphoma cell lines

A simple fluorometric assay for the determination of cell numbers

A sensitive fluorometric assay was developed for the enumeration of cells in microtiter plates. This assay is based on the fluorescence enhancement of propidium iodide (PI) upon binding with double-stranded nucleic acids. This fluorochrome is compatible with a wide range of reagents commonly used in the laboratory, thus washing the cells before staining is not necessary. PI, together with Triton-X 100 and EDTA, was added directly to the cell culture. After 16-18 h incubation at room temperature, intensity of fluorescence was determined with a micro-plate fluorometer. This quick and simple method is sensitive for as little as 1.95 x 10(3) mononuclear leukocytes, and provides a linear correlation (r = 0.999) between cell number and fluorescence up to 1 x 10(6) cells. Since PI has a large Stokes shift with excitation wavelength at common visible range and emission wavelength far out in the red region of the spectrum, it allows simultaneous detection of DNA and other fluorescent compounds such as calcein and fluorescein. This assay may prove to be a valuable alternative for cell number determination.

Group B streptococcus-induced nitric oxide production in murine macrophages is CR3 (CD11b/CD18) dependent

Nitric oxide (NO) is produced by murine macrophages in response to cytokines and/or gram-negative bacterial lipopolysaccharide. NO induction by gram-positive bacteria such as group B streptococci (GBS), the major etiologic agents of neonatal pneumonia and meningitis, has received little study. GBS as well as two other gram-positive bacterial species, Staphylococcus aureus and Staphylococcus epidermidis, were found to stimulate NO production in thioglycolate-elicited murine macrophages and in the mouse macrophage cell line J774A.1 in the presence of gamma interferon. Serotype Ia and III GBS were both stimulatory, as were asialo- and type antigen-deficient mutant strains of type III GBS. NO production was dose dependent, inhibitable by L-arginine analogs, and unaffected by polymyxin B. Since phagocytosis by murine and human phagocytes of GBS is dependent on complement receptor type 3 (CR3), the role of CR3 in the NO response to GBS was tested in the CR3-deficient myelomonocytic cell line WEHI-3. GBS did not induce NO, whereas S. aureus or lipopolysaccharide did induce NO in WEHI-3 cells. S. epidermidis, whose nonopsonic phagocytosis is also CR3 dependent, failed to induce NO in WEHI-3 cells. Monoclonal anti-CR3 (anti-CD11b or anti-CD18) in the presence of interferon also induced NO production in thioglycolate-elicited macrophages and in J774A.1 cells but not in WEHI-3 cells. This evidence suggests that ligated CR3 and gamma interferon act synergistically to induce NO production and that CR3 mediates the GBS-induced signal for NO production in interferon-treated macrophages.

Inhibition of human immunodeficiency virus type 1 replication by SDZ NIM 811, a nonimmunosuppressive cyclosporine analog

(Me-Ile-4)cyclosporin (SDZ NIM 811) is a 4-substituted cyclosporin which is devoid of immunosuppressive activity but retains full capacity for binding to cyclophilin and exhibits potent anti-human immunodeficiency virus type 1 (HIV-1) activity. SDZ NIM 811 selectively inhibits HIV-1 replication in T4 lymphocyte cell lines, in a monocytic cell line, and in HeLa T4 cells. Furthermore, its antiviral activity against laboratory strains and against clinical isolates from geographically distinct regions in primary T4 lymphocytes and in primary monocytes (50% inhibitory concentration = 0.011 to 0.057 micrograms/ml) was demonstrated. SDZ NIM 811 does not inhibit proviral gene expression or virus-specific enzyme functions, either free or bound to cyclophilin. The compound does not influence CD4 expression or inhibit fusion between virus-infected and uninfected cells. SDZ NIM 811 was, however, found to block formation of infectious particles from chronically infected cells. Oral administration to mice, rats, dogs, and monkeys resulted in levels in blood considerably exceeding the drug concentration, which completely blocked virus replication in primary cells. SDZ NIM 811 caused changes of toxicity parameters in rats to a smaller degree than cyclosporine (formerly cyclosporin A). Thus, the potent and selective anti-HIV-1 activity of SDZ NIM 811 and its favorable pharmacokinetic behavior together with its lower nephrotoxicity than that of cyclosporine make this compound a promising candidate for development as an anti-HIV drug.

Dimethyl sulfoxide modulates NF-kappa B and cytokine activation in lipopolysaccharide-treated murine macrophages

Antioxidants are protective against septic shock in animal models. Recently, free radical scavengers have been found to inhibit the activation of the NF-kappa B protein in a number of cell lines. This transcriptional regulatory protein binds to the promoters of the proinflammatory cytokines tumor necrosis factor, interleukin-6, and the macrophage inflammatory proteins. The current work examined lipopolysaccharide-induced NF-kappa B activation in the J774 macrophage-like cell line and primary peritoneal macrophages from lipopolysaccharide-responsive (C3HeB/Fej) and -nonresponsive (C3H/HeJ) murine strains. The DNA-binding activity of the NF-kappa B protein directly correlated with mRNA expression for the genes encoding the proinflammatory cytokines and the free radical scavenging enzyme, superoxide dismutase. Both the p50 and p65 NF-kappa B subunits were detected on gel supershift assays. Minimal NF-kappa B activity was observed following exposure of C3H/HeJ macrophages to lipopolysaccharide. The antioxidant dimethyl sulfoxide decreased the level of NF-kappa B activation in the J774 cells. This correlated with decreased expression of cytokine mRNAs and tumor necrosis factor bioactivity. These results suggest that modulation of NF-kappa B activation may provide a mechanism through which antioxidants protect against endotoxemia in murine models.

Multiple regulatory elements in the interleukin-6 gene mediate induction by prostaglandins, cyclic AMP, and lipopolysaccharide

Induction of interleukin-6 (IL-6) gene expression is mediated by numerous agents involving all major signal transduction pathways. We have compared the effects of prostaglandins and their second messenger cyclic AMP (cAMP) with the effect of lipopolysaccharide (LPS) on IL-6 gene expression. We demonstrate that secretion of IL-6 is induced by cAMP in murine monocytic PU5-1.8 cells, even though to a lesser extent than by LPS. Nevertheless, cAMP and prostaglandins of the E series in the presence of theophylline induce transcription of the IL-6 promoter more strongly than LPS, suggesting distinctive effects of cAMP and LPS on posttranscriptional events. Mutations within four regulatory elements, namely, the multiple response element (MRE), AP-1, NF-IL6, and NF-kappa B sites, significantly reduce, but do not completely abrogate, inducibility by cAMP and prostaglandin E1, whereas alterations of four additional sites have no effects. LPS-induced promoter activity, however, is almost completely abolished by mutations in the NF-kappa B site, suggesting that a single regulatory element is crucial for inducibility by LPS. Stimulation by cAMP is correlated with the binding of inducible factors to the AP-1, NF-IL6, and NF-kappa B elements, whereas factors binding to the MRE are constitutively expressed. Recombinant cAMP response element-binding protein binds to the MRE, indicating a potential role for this factor in the cAMP response. Our results suggest that cAMP and prostaglandins act through multiple, partially redundant regulatory elements to induce IL-6 expression in monocytic cells. Nuclear events that overlap partially with the LPS response but also exhibit distinctive features are involved.

Multiple regulatory elements in the interleukin-6 gene mediate induction by prostaglandins, cyclic AMP, and lipopolysaccharide

Induction of interleukin-6 (IL-6) gene expression is mediated by numerous agents involving all major signal transduction pathways. We have compared the effects of prostaglandins and their second messenger cyclic AMP (cAMP) with the effect of lipopolysaccharide (LPS) on IL-6 gene expression. We demonstrate that secretion of IL-6 is induced by cAMP in murine monocytic PU5-1.8 cells, even though to a lesser extent than by LPS. Nevertheless, cAMP and prostaglandins of the E series in the presence of theophylline induce transcription of the IL-6 promoter more strongly than LPS, suggesting distinctive effects of cAMP and LPS on posttranscriptional events. Mutations within four regulatory elements, namely, the multiple response element (MRE), AP-1, NF-IL6, and NF-kappa B sites, significantly reduce, but do not completely abrogate, inducibility by cAMP and prostaglandin E1, whereas alterations of four additional sites have no effects. LPS-induced promoter activity, however, is almost completely abolished by mutations in the NF-kappa B site, suggesting that a single regulatory element is crucial for inducibility by LPS. Stimulation by cAMP is correlated with the binding of inducible factors to the AP-1, NF-IL6, and NF-kappa B elements, whereas factors binding to the MRE are constitutively expressed. Recombinant cAMP response element-binding protein binds to the MRE, indicating a potential role for this factor in the cAMP response. Our results suggest that cAMP and prostaglandins act through multiple, partially redundant regulatory elements to induce IL-6 expression in monocytic cells. Nuclear events that overlap partially with the LPS response but also exhibit distinctive features are involved.

B lymphocyte and macrophage expression of carcinoembryonic antigen-related adhesion molecules that serve as receptors for murine coronavirus

The expression of carcinoembryonic antigen (CEA)-related glycoproteins that have been associated with intercellular adhesion and that serve as receptors for mouse hepatitis virus (MHV) was analyzed in cells from the immune system of BALB/c mice using immunolabeling and RNA polymerase chain reaction amplification of receptor transcripts. These glycoproteins, which are called biliary glycoproteins, were highly expressed in B lymphocytes, including cells of the B-1a (CD5+) lineage, and in macrophages, but were not detectable in resting T lymphocytes. Similarly, murine cell lines of B cell and macrophage origin expressed messenger RNA encoding CEA-related molecules, while the corresponding mRNA was only slightly detectable in a T cell line. These CEA-related cell adhesion glycoproteins were also expressed in endothelial cells. Therefore, their specific interaction with their so far unknown ligand may be of functional importance in cellular interactions in the immune response. Monoclonal antibody directed against these glycoproteins blocked MHV-A59 infection of the B cell-derived SP20 cell line. Thus, the functional receptors for MHV on B lymphocytes, like those on murine fibroblasts, are isoforms of CEA-related glycoproteins. Treatment of B cells with anti-receptor antibody also blocked B cell-mediated cytotoxicity against MHV-A59-infected fibroblasts, indicating that this phenomenon is mediated by interaction of viral attachment protein on the infected target cells with specific CEA-related receptor glycoproteins on the effector B cells.

Human hepatoma cells synthesize and secrete lysozyme: modulation by cytokines

Plasma lysozyme levels are elevated in several different pathological conditions. In our study we show that well differentiated human hepatoma cells Hep3B and HepG2 are active synthesis sites of lysozyme and that this synthesis can be modulated by acute phase mediators. The production and modulation of lysozyme synthesis was studied by means of Northern-blot analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and a specific bioassay after treatment of the cells with interleukin-1 beta, interleukin-6 and tumor necrosis factor-alpha. Hep3B and HepG2 cells constitutively synthesize high amounts of lysozyme. Lysozyme synthesis and secretion were found to be augmented by interleukin-1 beta and tumor necrosis factor-alpha in both cell lines. Interleukin-6 caused an increase in lysozyme production in Hep3B but a decrease in the HepG2 cells. As expected, the synthesis of albumin was decreased in both cell lines. Furthermore we demonstrated that HepG2 and Hep3B cells produce a biologically active form of the enzyme as measured by a specific bioassay. The results demonstrate that lysozyme is constitutively synthesized by Hep3B and HepG2 hepatoma cell lines and that lysozyme synthesis is modulated by acute-phase mediators. Well differentiated human hepatoma cells may respond differently to different cytokines.

A new rapid and simple non-radioactive assay to monitor and determine the proliferation of lymphocytes: an alternative to [3H]thymidine incorporation assay

A one-step non-radioactive assay to determine the proliferation of murine lymphocytes, lymphoid tumor cells and hybridoma cells is described. This assay requires the addition of Alamar Blue dye to cell cultures and the degree of change in its color, which is reflective of the extent of cellular proliferation, can be determined by an ELISA plate reader. Alamar Blue must be added during the initial phase of cell culture. The pattern of concanavalin A (ConA) or anti-CD3 antibody-induced proliferative response of murine lymphocytes as assessed by Alamar Blue was similar to that of a [3H]thymidine assay. Similarly, the spontaneous proliferation curve of anti-CD3 antibody secreting cell line (YCD3-1), monocytic macrophage cell lines (PU5-1.8, P388D1, J774.1) and myeloma cells (Sp2/0) as determined by Alamar Blue closely resembled that of the [3H]thymidine assay. The minimum detectable number of proliferating cells was comparable in Alamar Blue and [3H]thymidine assays. Since cell lysis/extraction and washing procedures are not involved in the Alamar Blue assay, this approach has several distinct advantages over currently available assays (eg. [3H]thymidine). First, it allows daily monitoring of proliferation without compromising the sterility of cultures. An indication of proliferation can be evaluated (spectrophotometrically or visually) as early as 24 h after ConA stimulation. Second, unlike previously reported assays, Alamar Blue permits further analysis of proliferating cells by other methods. Analysis of cells in culture with Alamar Blue for various surface antigens (CD44, CD45RB, CD4, heat stable antigen) by flow cytometry revealed that the fluorescent profile and relative percentage of cells in cultures with the Alamar Blue were comparable to those without this reagent. The salient advantages of Alamar Blue assay over the [3H]thymidine assay include: (i) non-radioactivity; (ii) simplicity; (iii) less costly; (iv) non-labor intensive; (v) rapidity of assessment of proliferation of large number of samples; (vi) non-toxicity; (vii) usefulness in determining the kinetics of cell growth of hybridomas; and (viii) non-interference of secretion of antibodies by a hybridoma cell line.

Promoter activity of the 1731 Drosophila retrotransposon in a human monocytic cell line

The resemblance between retrotransposons and retroviruses suggests an evolutionary relationship and indicates that they may share common transcription factors. We have analyzed the behaviour of the Drosophila 1731 retrotransposon promoter in the human monocytic U937 cell line. We show that the long terminal repeat (LTR) of 1731 promotes CAT (chloramphenicol acetyl transferase) activity in these cells, in which it is enhanced by phorbol esters. Using gel mobility assays, we detected a human nuclear protein that binds in the U3 region of the LTR in a sequence-specific manner. Its precise target was determined by a DNase I footprinting experiment.

Modulation of chemiluminescence in a murine macrophage cell line by neuroendocrine hormones

This study determined the effects of neuropeptides and neuroendocrine hormones at the cellular level of the immune response using a murine macrophage cell line, J774, which exhibits a chemiluminescent oxidative burst upon acute stimulation with zymosan. We report that the zymosan-triggered oxidative burst of J774 cells can be modulated by the opioid peptides beta-endorphin (beta-END) and dynorphin A (DYN) in a naloxone-reversible fashion. Norepinephrine (NE) also modulated chemiluminescence (CL) emission of J774 cells, with dose-dependent suppression of CL dependent upon co-incubation with gamma-interferon (gamma-INF). Without gamma-INF co-incubation, NE shared with the opioid peptides beta-END and DYN the ability to modulate oxidative burst, producing an inverted-U dose response. These data indicate that J774 cells may be useful for explaining some mechanisms through which the neuroendocrine system interacts with the immune system.

A rapid and simple microfluorometric phagocytosis assay

A microfluorometric method for phagocytosis study has been developed using fluorescein conjugated Escherichia coli K-12 particles. This technique is based on the uptake of fluorescent particles and quenching of extracellular fluorescence at the end of the assay. A murine macrophage cell line, J774, was used as a phagocyte model. The cells were harvested from tissue culture flasks and adjusted to 1 x 10(6) cells/ml. They were then dispensed into a 96-well tissue culture plate, 100 microliters/well, and incubated at 37 degrees C in 5% CO2 for 1 h to allow cells to adhere to the bottom of the wells. The culture medium was aspirated and 100 microliters of fluorescent E. coli particles suspended in Hanks' buffer were added. The plates were further incubated for various time periods. Buffer solution in the wells was removed by aspiration. Extracellular fluorescence was then quenched by adding 100 microliters of trypan blue (250 micrograms/ml, pH 4.4). The dye was removed after 1 min. The intensity of fluorescence associated with intracellular fluorescent particles was measured directly in the wells using a computerized microplate fluorometer at 485 nm excitation and 530 nm emission. This assay provided a rapid and objective measurement of phagocytosis activity. Using a cultured cell line and a 96-well microtiter plate format, this assay can facilitate the screening of a large number of various biological and pharmacological substances for their modulating effects on phagocytosis.

Characterization of prostaglandin E2 receptors expressed on human monocytic leukaemic cell line, U937

Prostaglandin E2 (PGE2) receptors of a human monocytic leukaemic cell line, U937 cells, have been identified. [3H]PGE2 binding to these cells was found to be saturable and highly specific. Scatchard analysis of binding data revealed a non-linear plot indicating the presence of two independent classes of binding sites with different affinities and capacities. The high-affinity class had Kd1 = 3.1 nM and binding capacities n1 = 0.6 fmol/10(6) cells, whereas the low-affinity class had Kd2 = 137 nM and capacities n2 = 16 fmol/10(6) cells. Incubation of U937 cells with 3 microM PGE2 stimulated a 15-fold increase in cAMP formation compared to basal levels. Prior exposure of these cells with 10 microM PGE2 for 60 min induced both homologous and heterologous desensitization of adenylate cyclase activity. PGE2 (3 microM) or histamine (100 microM) showed reduced stimulation of cAMP formation in these desensitized cells compared to controls. The desensitized cells also showed 80% reduction of specific PGE2 binding compared to control cells. Our data suggest that U937 cells have PGE2 receptors which are linked to the adenylate cyclase system.

An automated micro-fluorometric assay for monitoring oxidative burst activity of phagocytes

A micro-fluorometric assay using 2',7'-dichlorofluorescein diacetate (DCFH-DA) to monitor oxidative burst (OB) in phagocytes has been developed. This assay is based on the oxidation of nonfluorescent DCFH-DA to highly fluorescent 2',7'-dichlorofluorescein (DCF) both intracellularly and extracellularly. A murine macrophage cell line, J774, and a human monocytic cell line, Mono Mac 6, were used as models. The cells were harvested from tissue culture flasks, washed, counted and adjusted to desired concentrations. They were then dispensed into a 96-well flat-bottom tissue culture plate. After adding DCFH-DA and an agent eliciting OB, the plates were incubated in 5% CO2 at 37 degrees C for various periods. The intensity of fluorescence was measured directly in the wells of the tissue culture plate with the cells in situ using a computerized microplate fluorometer at 485 nm excitation and 530 nm emission. This assay provided a rapid measurement of oxidative burst of phagocytes. The automated micro-fluorometric assay may be suitable for screening the immunomodulating activities of various biological and pharmacological substances.

Immunoenzymatic assay that measures the expression of murine histocompatibility antigens in macrophages and lymphocytes

A convenient--simple, sensitive, rapid and reproducible--enzyme immunoassay to measure H-2 particulated and solubilized cellular antigens is described. Cellular antigens were measured by ELISA through the binding of specific biotinylated antibodies and streptoavidin-peroxidase conjugate to cells in suspension. Endogenous peroxidase activity of activated cells was inhibited by addition of sodium azide and H2O2 in acid conditions. The assay proved capable of distinguishing between two cell lines (EL-4/H-2b and P815/H-2d) and even between the cells of three congenic mouse strains (BALB/B, H-2b, BALB/c, H-2d, and BALB/K, H-2k) and was sensitive to as few as 2.5 x 10(4) cells/well. Results were comparable to those obtained with FACS. An inhibition version of this assay was found to be very useful for the detection of H-2 antigens present in whole antigen cells extracts.

Direct visualisation and quantification of cellular cytotoxicity using two colour flourescence

A fluorescence method is described for the evaluation of cell death induced by cellular cytolytic activity. A green fluorescent membrane dye, D275, was used to label various target cell lines and propidium iodide (PI) uptake was used to assay cell death. Natural killer (NK), lymphokine activated killer (LAK) as well as targeted T cell mediated cellular cytotoxicity were quantified using the fluorescence method and compared to results obtained with the 51chromium (51Cr) release assay. A good correlation was found after an assay period of 4-8 h indicating that the fluorescence method is a reliable alternative to the 51Cr release assay.

Tumor-associated karyotypic lesions coselected with in vitro macrophage differentiation

Several cytogenetic lesions in chromosomes 2, 5, 12, and 16 have been repeatedly coselected with in vitro macrophage differentiation in a clonal murine thymic tumor cell line. Parental-type subclones, which show an extremely immature hemopoietic phenotype, do not carry the aberrations. The frequency of the stable differentiated variants is elevated by 5-azacytidine and bromodeoxyuridine, consistent with chromosome breakage being responsible for the phenotype. The frequency is also raised by dexamethasone. Since variants are 300-3,000-fold more resistant to dexamethasone than parental clones, we interpret this to be largely due to selection. Three of the lesions, on chromosome 2, match those previously described as associated specifically with in vivo-generated murine myeloid tumors, induced by X irradiation and corticosteroid treatment. Several implications follow from these observations. (1) In vitro differentiation in clonal tumor cell lines can be used to select for tumor-associated lesions. This should allow genetic and molecular analysis of the chromosome 2 lesions and of others that may pinpoint genes critical to macrophage differentiation and transformation. (2) Myeloid and lymphoid tumors that occur in response to X irradiation may diverge from a common initiating tumor. (3) The hemopoietic lineage switch phenomenon, previously described by several authors, may be caused by similar or identical chromosome aberrations.

Diverse classes of T-cell lymphomas arise in T-lymphocyte-inductive epitheliomas of the mouse salivary gland

During the course of serial transplantations of polyomavirus-induced C3H-Bittner salivary gland epitheliomas in F1-hybrid mice, three tumor sublines were found which gave rise to T-cell lymphomas of host origin. The lymphomas resembled spontaneous AKR/J thymic lymphomas in their expression of lymphoid differentiation antigens, and they may represent sequential stages in the differentiation of immature T lymphocytes. We found no evidence that polyomavirus directly induced the lymphomas, rather, the lymphomagenic events paralleled those which occur in spontaneous AKR/J thymic lymphomas.

The mouse M-lysozyme gene domain: identification of myeloid and differentiation specific DNasel hypersensitive sites and of a 3'-cis acting regulatory element

The mouse M-lysozyme gene is exclusively expressed in myeloid cells of the blood system being progressively turned on upon cell differentiation. In this study the mechanism controlling this tissue- and differentiation stage-specific gene expression was analyzed at the level of chromatin structure. A complex pattern consisting of constitutive and differentiation dependent DNasel hypersensitive sites (HSs) was found in a set of various myeloid cell lines, representing different stages of maturity. The chromatin of a lymphoid cell line, which does not express the lysozyme gene, is completely insensitive to DNasel digestion. Chromatin analysis of two multipotent hematopoietic stem cell lines which can be differentiated in vitro to mature myeloid cells confirmed that these identified DNasel HSs are specific for distinct differentiation stages, rather than being a characteristic feature of the cell lines. Additionally, the stem cell studies revealed that the hypersensitivity of the chromatin domain is already established at the multipotent stage. DNA fragments spanning a cell type- and differentiation stage-specific cluster of HSs in the 3' region of the gene showed enhancer activity in all cell types tested. In the light of this lack of specificity, we suggest that cell type-specific modification of the chromatin structure in this region may play a role in determining the binding of a widespread transcription factor, and hence contribute to the time specificity of lysozyme M gene expression.

Opsonin-independent phagocytosis of group B streptococci: role of complement receptor type three

The role of complement receptor type 3 (CR3) in nonopsonic recognition of group B streptococci (GBS) by macrophages was investigated. Monoclonal anti-CR3 (anti-Mac-1) inhibited phagocytosis of GBS strains by as much as 50% in serum-free cultures of both mouse peritoneal macrophages and the macrophage cell line PU5-1.8. GBS uptake was unaffected by the presence of anti-C3 or salicylhydroxamate, an inhibitor of the covalent binding reaction of C3. Soluble antibodies to LFA-1 or to the common beta-chain (CD18) of the LFA-1/CR3/p150,95 family of cell adhesion molecules did not inhibit GBS uptake. Down-modulation of surface Mac-1 on macrophages following adherence to anti-Mac-1- or anti-CD18-coated surfaces also inhibited uptake of GBS. Further evidence for GBS interaction with CR3 was demonstrated by reduction of EC3bi rosette formation in macrophages adherent to GBS-coated plates. These studies suggest that GBS can interact with macrophage CR3, promoting phagocytosis in a C3-independent fashion. In the absence of specific immunity in neonates, this recognition mechanism may be a significant virulence determinant for GBS which poorly activate the alternate complement pathway.

Complex formation of human T-cell leukemia virus type I p40tax transactivator with cellular polypeptides

We examined cellular components which associate with p40tax, the viral transactivation molecule of human T-cell leukemia virus type I. Such molecules were searched by immunoprecipitation with polyclonal and monoclonal antibodies specific for p40tax. Two cellular proteins with molecular masses of 95 kDa (p95) and 60 kDa (p60) were specifically coprecipitated with p40tax from extracts of all p40tax-producing cell lines but not from p40tax-negative cell lines. The p60 component was also shown to associate with p40tax in vitro, by using radiolabel-chase experiments. Rabbit antisera specific for p60 and p95 were prepared by immunization with electrophoretically purified molecules. While anti-p95 antiserum coprecipitated p40tax, no p40tax could be identified in immunoprecipitates by using a polyclonal anti-p60 antiserum. The partial amino acid sequence of p60 demonstrated that p60 is identical to the human 60-kDa heat shock protein (a member of the chaperonin family of proteins). Although the biological significance of the complex formation of p40tax with p95 and p60 has yet to be determined, it may be that the complex formation is one of the mechanisms by which the biological activity of p40tax can be regulated.

A new DNA profiling system for cell line identification for use in cell banks in Japan

Using the polymorphic DNA probes, ChdTC-15, ChdTC-114, pYNH24, and lambda TM-18, a DNA profiling system was developed that verified identities of individual cultured cell lines collected in the Japanese cell banks, JCRB, RCB, and IFO. These highly polymorphic DNA probes include both VNTR (Variable Number of Tandem Repeats) sequences and substantial lengths of unique regions. In the mixed probe system, several distinct bands from four to eight can be used for cell line identification. These bands were widely spread in a range of molecular sizes, and were stable and reproducible under stringent conditions of Southern blot hybridization. Because the DNA profile was specific for each individual human cell line, it is useful not only to authenticate many existing cultured cell lines but also to monitor their identity during propagation in a laboratory, and to confirm newly established lines as unique.

The characteristics of macrophage-like cell lines derived from normal sheep spleens

Macrophage-like cell lines were derived from sheep spleens using conditioned medium from L-929 mouse cells as a source of colony stimulating factor. In seven out of ten attempts colonies of macrophage-like cells appeared after 2-3 weeks of culture. The cells were established in culture as cell lines, and survived 120 passages. They were strongly (+ +) positive for non-specific esterase but negative for peroxidase and produced detectable but small amounts of lysozyme (0.21-1.76 micrograms/10(6) cells). Latex particles were actively phagocytosed. Bacteria (Staphylococcus albus, Staphylococcus aureus) attached to the cell surface and were internalized in the presence of specific antibody. Expression of receptors for immunoglobulin and complement varied somewhat between the different cell lines: the proportion of receptor-bearing cells ranged between 9 and 26% FC-receptors, and 10 and 38% for C-receptors. The cell lines displayed a peculiar karyotype as well as protein profile that were different from normal sheep but similar between the different cell lines. Culture supernatants of the cell lines contained a colony stimulating activity which was used to establish further cell lines. They also spontaneously produced an interleukin-1-like activity that had no effect on baseline proliferation of sheep lymphocytes but enhanced their response to PHA (1.7-fold) particularly in conjunction with sheep IL-2 (4-fold). Prostaglandin E2 was produced in a growth-cycle dependent manner: the peak production occurred on the second day (77-140 pg/ml) at 2 x 10(5) cells and declined to 33-50 pg/ml on the eighth day when cell numbers had increased to 2-3 x 10(6). These easily cultured cell lines derived from normal tissue without the introduction of viral DNA should provide a useful source of material for studies of macrophage function in sheep.

DNase I hypersensitive sites flank the mouse class II major histocompatibility complex during B cell development

The mouse class II major histocompatibility complex (MHC) encodes a polymorphic, multigene family important in the immune response, and is expressed mainly on mature B cells, on certain types of dendritic cells and is also inducible by gamma-interferon on antigen presenting cells. To study the regulatory elements which control this expression pattern, we have examined the chromatin structure flanking the class II MHC region, in particular during B cell differentiation. Using a panel of well-characterised mouse cell lines specific for different stages of B cell development (pre-B, B, plasma cell) as well as non-B cell lines, we have mapped the DNase I hypersensitive (DHS) sites adjacent to the mouse MHC class II region. The results presented show, for the first time that there are specific hypersensitive sites flanking the class II MHC locus during pre B cell, B cell and plasma cell stages of B cell differentiation, irrespective of the status of class II MHC expression. These hypersensitive sites are not found in T cell, fibroblast or uninduced myelomonocytic cell lines. This suggests that these DHS sites define a developmentally stable, chromatin structure, which can be used as a marker of B cell lineage commitment and may indicate that a combination of these hypersensitive sites reflect regulatory proteins involved in the immediate expression of a particular class II MHC gene or possibly control of the entire locus.

Stage-specific expression of intracisternal A-particle sequences in murine myelomonocytic leukemia cell lines and normal myelomonocytic differentiation

The levels of intracisternal A-particle (IAP) mRNA were analyzed in a variety of myelomonocytic leukemia cell lines, peritoneally derived macrophages, and normal hemopoietic progenitors induced to differentiate. In both normal and leukemic cells, the highest level of IAP message was found in cells at an intermediate stage of myelomonocytic differentiation, namely, the promyelomonocyte. These results indicate that IAP sequence transcription is regulated differentially during myelomonocytic cell development and that in general, the expression pattern is preserved in leukemic cell lines in vitro. In addition, Northern (RNA) analysis detected only type I IAP transcripts as the major IAP message and the expressed IAP subtypes varied in certain cell lines. This is the first comprehensive study of IAP expression in the myelomonocytic lineage and provides a useful system to study the biology of IAPs.

Stage transitions in B-lymphocyte differentiation correlate with limited variations in nuclear proteins

Total nuclear proteins extracted from cell lines representing various stages of differentiation of mouse B lymphocytes were studied by computer analysis of two-dimensional gels. Of the 1438 spots present on the gels, 55 varied significantly in intensity during differentiation. The variations occurred most often in steps correlating with those classically defined for B-cell differentiation. Seventeen spots were not detectable in at least one of the stages (qualitative variations) and could represent switching on or off of genes coding for nuclear proteins. Detailed analysis of the 55 variable spots showed that they fall into small sets characterized by similar expression profiles, which argues for a combinatorial, multistep control mechanism of gene expression. In addition, analysis of the expression of all the nuclear proteins resolved on the gels clearly differentiated B-lineage cells from myeloid cells and suggested that the most important transition in B-cell differentiation occurs between the resting B cell and plasmocyte stages.

Design, development, and interpretation of HIV neutralization assays

In developing therapeutic reagents for the control of HIV infection, it is necessary to screen candidate products in vitro for their ability to reduce or neutralize viral infection. Although the current literature describes numerous neutralization assays, no universally accepted standards have been adopted. In this article, we briefly review the available neutralization assays and describe in detail the methods we have selected in our laboratory for the screening and characterization of reagents with potential anti-HIV properties. After evaluating many different technical protocols and experimental procedures, we have found the syncytium inhibition and syncytial focus assays to be particularly useful and have found p24 gag antigen production to be an excellent objective measure of HIV infection under a variety of conditions. These assays proved reproducible and sensitive and are suitable for use in the majority of laboratories.

Phagocytic cell chemiluminescence using different zymosan preparations

This study compared the effectiveness of opsonized and unopsonized zymosan prepared in our laboratories with a commercially available opsonized preparation used for induction of luminol-dependent oxidative burst in phagocytic cells. The production of chemiluminescence (CL) by human whole blood, isolated human neutrophils, normal BALB c mouse splenocytes, and an immortal BALB c mouse macrophage cell line (J774A.1) was tested in an automated luminometer. Recombinant murine or human interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) were used as priming agents in some of the experiments. With human leukocytes and normal mouse spleen cells the laboratory-prepared zymosans (regardless of opsonization) induced equal or significantly greater CL than did the commercially prepared zymosan. In addition, greatly increased CL was evident with IFN-gamma- and LPS-primed neutrophils tested with our zymosans compared with the commercial preparation. These results suggest that effective zymosans capable of inducing strong, reproducible CL responses from several different phagocytic cell populations can be readily made in the laboratory.

Secretion of neurotoxins by mononuclear phagocytes infected with HIV-1

Mononuclear phagocytes (microglia, macrophages, and macrophage-like giant cells) are the principal cellular targets for human immunodeficiency virus-1 (HIV-1) in the central nervous system (CNS). Since HIV-1 does not directly infect neurons, the causes for CNS dysfunction in acquired immunodeficiency syndrome (AIDS) remain uncertain. HIV-1-infected human monocytoid cells, but not infected human lymphoid cells, released toxic agents that destroy chick and rat neurons in culture. These neurotoxins were small, heat-stable, protease-resistant molecules that act by way of N-methyl-D-aspartate receptors. Macrophages and microglia infected with HIV-1 may produce neurologic disease through chronic secretion of neurotoxic factors.

Lysozyme synthesis in osteoclasts

Osteoclasts may or may not be directly related to monocytes and macrophages, but it is well established that these cell types share a number of features in common. In the present study we sought to extend this comparison by assessing lysozyme synthesis in osteoclasts, an enzyme known to be produced and secreted in large amounts by monocytes and macrophages. Our data show that freshly isolated chicken osteoclasts and osteoclasts in situ contain an abundant amount of lysozyme and correspondingly high steady-state levels of the enzyme's messenger RNA. Marrow macrophages, at various stages of in vitro maturation, also possess lysozyme mRNA but in amounts approximately two to four times lower than osteoclasts. These observations reaffirm the monocyte-macrophage nature of the osteoclast but raise questions about the function of the lysozyme in this cell. At present, the role of the lysozyme in osteoclast activity remains unexplained.

Functional comparison of the inductions of NADPH oxidase activity and Fc gamma RI in IFN gamma-treated U937 cells

The capacity to generate superoxide anion (O2-) can be induced in U937 cells by various agents known to cause myeloid cell differentiation. Other reported differentiation events include diminished cell proliferation and the induction by gamma-interferon (IFN gamma) of Fc receptors for immunoglobulin G1 (Fc gamma RI). In this study, we differentiated U937 cells and high Fc gamma RI-expression mutants of U937 cells by treating them with IFN gamma. We compared the time courses over which surface Fc gamma RI became maximal, NADPH oxidase activity was induced, and the antiproliferative effect of IFN gamma was detected. Oxidase activity was measured by stimulating cells with PMA or by activating surface Fc gamma RI using aggregated human IgG1 or second antibody crosslinking of mAb 32/Fc gamma RI complexes. We found that IFN gamma in the absence of additional lymphokines induced high levels of oxidase activity in maximally differentiated U937 cells with even higher levels in the fully differentiated high-Fc gamma RI expression mutants (greater than 8 nmoles/10(6) cells/min for A12.13 cells). Over the course of differentiation, maximal induced levels of Fc gamma RI were reached after 1 to 2 days of IFN gamma treatment, prior to the antiproliferative effect of the lymphokine. In contrast, oxidase activity was induced after a lag of approximately 2 days, becoming maximal only after 4 to 6 days of IFN gamma treatment. This comparison of the induction of Fc gamma RI with that of oxidase activity triggered through Fc gamma RI indicated that the rapid increase of surface receptor was not accompanied by a completion of the pathway of Fc gamma RI-mediated oxidase activity. However, the time courses of induction detected by PMA and Fc gamma RI-agonists were coincident suggesting that the development of oxidative capacity could be due to the induction of components required by both the PMA- and surface receptor-mediated pathways. There are several oxidase components that are known to be IFN gamma-inducible, such as the oxidase flavoprotein, a b558 cytochrome peptide, and oxidase-requiring cytosolic components, and it is possible that one or a set of these components could be the limiting factor(s) for IFN gamma-induced oxidase activity.

Characterization of mouse macrophage differentiation antigens by monoclonal antibodies

Monoclonal rat antibodies to mouse macrophage antigens were prepared. For immunization phagocytic cells in the spleens of mice recovering from sublethal irradiation were used. Specificities of the monoclonal antibodies obtained were determined on cells of normal mouse cell populations as well as on cells of a panel of mouse cell lines. In an attempt to monitor expression of differentiation-related antigens two models of in vitro-induced macrophage differentiation were used: differentiation of cells of the myeloblast line Ml; CSF-1-induced differentiation of bone marrow cells. The results obtained clearly show that during maturation from undifferentiated to highly differentiated cells of the macrophage lineage expression of antigens recognized by the MIV 38, MIV 55, MV 87, and MV 114 monoclonal antibodies is enhanced. At the same time, expression of antigens recognized by the MIV 52, MIV 113, and MIV 116 monoclonal antibodies diminishes at a similar rate. The suitability of these monoclonal antibodies for the characterization of differentiation states of mouse macrophages is discussed.

Salmonella typhi vaccine strain in vitro; low infectivity in human cell line U937

Salmonella typhi strain Ty21a has been used for live oral vaccine. The infectivity of Ty21a, in comparison with S. typhi Ty2, was evaluated using the human monocyte-macrophage cell line U937. Assays were performed by quantitative microscopy and viable count technique. Ty2 infected approximately 100% of the cells, multiplied extensively within these cells and caused cell death. The same dose of Ty21a infected only about 15% of the cells, resulting in a low number of intracellular bacilli and cell survival. The use of gentamicin in the test confirmed intracellular multiplication of Ty2 but not Ty21a. The system described may be suitable as a test system for characterization of the degree of virulence of Ty21a and other live, oral typhoid vaccines.

Growth factor gene activation and clonal heterogeneity in an autostimulatory myeloid leukemia

Cell lines were isolated from an in vivo-passaged myelomonocytic leukemia, WEHI-274, that arose in a mouse infected with the Abelson leukemia virus-Moloney leukemia virus complex. Clones were isolated in vitro in the presence or absence of a source of a hemopoietic growth factor, interleukin-3 (IL-3), and were divisible into three distinct classes. All three classes were leukemogenic in vivo. In vitro, the class I clone grew slowly at low cell density but responded with an increased growth rate to IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), and autoconditioned medium. Supernatants of these cultures contained a factor with the biological, biochemical, and antigenic properties of IL-3. Class II clones grew better in vitro at low cell densities than did the class I clone and also responded with an increased growth rate to IL-3, GM-CSF, and autoconditional medium but produced GM-CSF rather than IL-3. In contrast, class III clones died in vitro at all cell densities unless exogenous IL-3 or GM-CSF was added. Moreover, they produced no autostimulatory factors. In the class I and class II clones, one allele of the respective IL-3 or GM-CSF gene is rearranged, and in each case, grossly abnormal RNA transcripts of the rearranged gene are present. Neither rearrangements nor abnormal RNA transcripts of the IL-3 or GM-CSF gene were detected in the class III clones. All three classes exhibited a common rearrangement of the c-myb gene, which suggested that all were derived from the one ancestral cell. These experiments demonstrate that two distinct and independent autostimulatory events were involved in the progression of a single disease.

Calcitriol enhances transcriptional activity of lysozyme and cathepsin D genes in U937 promonocytes

Calcitriol (1,25-dihydroxyvitamin D3) has been reported to enhance the rate of synthesis of lysozyme [Rouis, Thomopoulos, Louache, Testa, Heroy & Titeux, (1985) Exp. Cell Res. 157, 539-543] and of cathepsin D [Stein, Braulke, von Figura & Hasilik (1987) Biol. Chem. Hoppe-Seyler 368, 413-418] in human promonocytes U937. In this study we show hat the hormone enhances the steady-state levels of cathepsin D and lysozyme mRNAs. The enhancement of the latter but not of the former is strongly inhibited by cycloheximide. The degradation rates of cathepsin D and lysozyme mRNAs as revealed in the presence of actinomycin D are not significantly affected by the treatment of the cells with calcitriol. In nuclei prepared from calcitriol-treated cells, an enhanced rate of synthesis of cathepsin D and lysozyme mRNA precursors is observed. These results suggest that in human promonocytes the rate of the transcription of cathepsin D and lysozyme genes is enhanced in the presence of calcitriol and that the regulation by the hormone of the transcription of lysozyme gene involves a short-lived or an induced protein.

The human lysozyme gene. Sequence organization and chromosomal localization

We have isolated two overlapping recombinant lambda-phage clones from a genomic lambda-EMBL3 library containing 25 kb of the human lysozyme gene region. Furthermore a full-lenght human lysozyme cDNA clone of 1.5 kb was isolated from a human placenta cDNA library. Nucleotide sequences of the entire structural gene and the cDNA clone were determined. The human lysozyme gene spans 5856 bp and its sequence organization with four exons and three introns is homologous to the chicken lysozyme gene and the human alpha-lactalbumin gene. Human and chicken lysozyme genes differ mainly in the size of their introns and 3' non-coding region. Four Alu repetitive elements were found in the human lysozyme gene, one in each intron and one on the fourth exon. Lysozyme transcripts of 1.6 kb and 0.6 kb in size were detected in human myeloid cell lines U-937, HL-60 and THP-1 and surprisingly in human hepatoma cell lines HepG2 and Hep3B. The lysozyme gene locus was assigned to human chromosome 12 by hybridization to a panel of DNAs from human-rodent somatic cell hybrids.

Growth factor gene activation and clonal heterogeneity in an autostimulatory myeloid leukemia

Cell lines were isolated from an in vivo-passaged myelomonocytic leukemia, WEHI-274, that arose in a mouse infected with the Abelson leukemia virus-Moloney leukemia virus complex. Clones were isolated in vitro in the presence or absence of a source of a hemopoietic growth factor, interleukin-3 (IL-3), and were divisible into three distinct classes. All three classes were leukemogenic in vivo. In vitro, the class I clone grew slowly at low cell density but responded with an increased growth rate to IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), and autoconditioned medium. Supernatants of these cultures contained a factor with the biological, biochemical, and antigenic properties of IL-3. Class II clones grew better in vitro at low cell densities than did the class I clone and also responded with an increased growth rate to IL-3, GM-CSF, and autoconditional medium but produced GM-CSF rather than IL-3. In contrast, class III clones died in vitro at all cell densities unless exogenous IL-3 or GM-CSF was added. Moreover, they produced no autostimulatory factors. In the class I and class II clones, one allele of the respective IL-3 or GM-CSF gene is rearranged, and in each case, grossly abnormal RNA transcripts of the rearranged gene are present. Neither rearrangements nor abnormal RNA transcripts of the IL-3 or GM-CSF gene were detected in the class III clones. All three classes exhibited a common rearrangement of the c-myb gene, which suggested that all were derived from the one ancestral cell. These experiments demonstrate that two distinct and independent autostimulatory events were involved in the progression of a single disease.

Expression of c-kit gene products in known cellular targets of W mutations in normal and W mutant mice--evidence for an impaired c-kit kinase in mutant mice

The proto-oncogene c-kit, a transmembrane tyrosine protein kinase receptor for an unknown ligand, was shown recently to map to the dominant white spotting locus (W) of the mouse. Mutations at the W locus affect various aspects of hematopoiesis, as well as the proliferation and/or migration of primordial germ cells and melanoblasts during development. Here, we show that c-kit is expressed in tissues known to be affected by W mutations in fetal and adult erythropoietic tissues, mast cells, and neural-crest-derived melanocytes. We demonstrate that the c-kit associated tyrosine-specific protein kinase is functionally impaired in W/WV mast cells, thus providing a molecular basis for understanding the developmental defects that result from these mutations.

Negative control region at the 5' end of murine leukemia virus long terminal repeats

Using in vitro protein binding and in vivo functional studies, we have identified novel regulatory sequences near the 5' end of murine leukemia virus (MuLV) long terminal repeats (LTRs). These sequences are highly conserved in all MuLV LTRs as well as in feline leukemia virus and gibbon ape leukemia virus LTRs. In this upstream conserved region (UCR), gel retardation assays detected two overlapping but distinct binding sites (UCR-U and UCR-L) for nuclear proteins (UCRF-U and UCRF-L). Three lines of evidence suggest a negative regulatory role for the UCR in viral transcription: (i) an inverse correlation was found between MuLV transcripts and nuclear proteins binding the UCR in the spleens of five different mouse strains; (ii) in vivo treatment of NFS mice with lipopolysaccharide resulted in the induction of splenic viral transcripts and the concomitant disappearance of UCR-binding proteins; and (iii) in mouse L cells transfected with an MuLV LTR linked to the chloramphenicol acetyltransferase (CAT) gene, cotransfected UCR oligonucleotides increased CAT expression, presumably by competing for inhibitory trans-acting factors.

Immune status of a mu, kappa transgenic mouse line. Deficient response to bacterially related antigens

We have examined the immune repertoire and immune response of a mouse that carries transgenes for a mu heavy chain and kappa light chain. The expression of these genes is under the regulation of their own controlling elements. The transgenes are expressed early in ontogeny and are easily detectable from day 13 of gestation onwards. The pre-B cells seem to function normally as they generate IgM-secreting colonies at normal frequencies. Colonies show predominantly the transgenic specificity. Expression of the transgenes is not limited to B cells since around 10%-20% of peripheral T cells and 50% of thymocytes express the mu transgene as an intracellular protein. Ectopic expression of kappa was not seen. The spleen size of the transgenic mouse is decreased by around 20%; this reduction is largely caused by a reduction of the B cell pool. Almost all B cells express the transgenes, only 30% co-express endogenous heavy chain genes and all co-express endogenous light chain genes. Serum Ig levels for IgM and IgA were normal, 20% of the IgM consist of the transgenic product. Serum IgG levels were decreased. T cell functions (helper and cytotoxic) were normal. Immune responses to conventional antigens were impaired, especially in the early phases of the immune response, but after boosting they were virtually normal, except for IgG3 which remained low. Primary antibody responses to T cell-independent antigens of the class II type (bacterially related antigens) were absent, although precursor frequencies for these antigens were within the expected range. The significance of this finding, as it relates to allelic exclusion of Ig genes, is discussed.

Negative control region at the 5' end of murine leukemia virus long terminal repeats

Using in vitro protein binding and in vivo functional studies, we have identified novel regulatory sequences near the 5' end of murine leukemia virus (MuLV) long terminal repeats (LTRs). These sequences are highly conserved in all MuLV LTRs as well as in feline leukemia virus and gibbon ape leukemia virus LTRs. In this upstream conserved region (UCR), gel retardation assays detected two overlapping but distinct binding sites (UCR-U and UCR-L) for nuclear proteins (UCRF-U and UCRF-L). Three lines of evidence suggest a negative regulatory role for the UCR in viral transcription: (i) an inverse correlation was found between MuLV transcripts and nuclear proteins binding the UCR in the spleens of five different mouse strains; (ii) in vivo treatment of NFS mice with lipopolysaccharide resulted in the induction of splenic viral transcripts and the concomitant disappearance of UCR-binding proteins; and (iii) in mouse L cells transfected with an MuLV LTR linked to the chloramphenicol acetyltransferase (CAT) gene, cotransfected UCR oligonucleotides increased CAT expression, presumably by competing for inhibitory trans-acting factors.

Deletion of c-ets1 and T3 gamma loci from the 11q- chromosome in the human monoblastic cell line U937

The 11q- chromosome in the human monoblastic cell line U937 appears to be derived from an interstitial deletion in bands 11q21-23/24 or a translocation with an unknown chromosome. We show here by in situ hybridisation that this chromosome has lost the c-ets1 and T3 gamma loci. C-ets1 and T3 gamma sequences were not detected on any chromosomes besides the normal 11, indicating either that they were lost from the genome or that the chromosome to which they were translocated was not present in a high enough proportion of the cells to be detected by in situ hybridisation. No DNA rearrangements were found with three different restriction enzymes in the c-ets1, N-CAM, Thy-1 and c-sea genes detected by our probes. There was also no detectable rearrangement in the c-fms gene which was shown to be translocated from chromosome 5 to chromosome 1 in a subline of U937. The size of the c-fms and c-ets1 messages were normal. The possible significance of these findings is discussed.

PB76: a novel surface glycoprotein preferentially expressed on mouse pre-B cells and plasma cells detected by the monoclonal antibody G-5-2

A monoclonal antibody (mAb) G-5-2 was isolated which binds to transformed as well as normal cells of the B lineage but not to cells of the T cell, myeloid lineages nor to fibroblasts. mAb G-5-2 reacts with pre-B and plasma cell-transformed lines, and it preferentially recognizes normal pre-B cells from fetal liver and bone marrow as well as plasma cells from spleen of mice. G-5-2+ fetal liver cells isolated by cell sorter express mRNA for mu heavy chain Ig gene and generate in vitro antibody-producing cells when co-cultured with lipopolysaccharide and rat thymocyte filler cells. During development the frequency and staining intensity of G-5-2+ cells in fetal liver from normal mice increases from 1% G-5-2+ cells at day 14 to approximately 7% positive cells at day 18 of gestation. Several strains or normal mice contain comparable numbers of G-5-2+ cells as well as B-220+ and BP-1+ B cell precursors in the fetal liver. Mice carrying the xid mutation have 3-4-fold less G-5-2+ as well as B-220+ and BP-1+ cells in the fetal liver, suggesting that the effects of the xid mutation may be manifested from early stages of B cell development. Fetal liver cells from mice carrying the scid mutation were found to contain normal numbers of G-5-2+ as well as B-220+ and BP-1+ pre-B cells. These results indicate that differentiation from progenitors to pre-B cells in scid mice may occur normally; the scid mutation would thus appear to affect the process of rearrangement and expression of the Ig genes in the developing pre-B cells. mAb G-5-2 precipitates a 76-kDa glycoprotein from surface-radiolabeled pre-B cells and plasma cells. Taken together, these results indicate that G-5-2 mAb recognizes a novel B cell lineage-specific surface molecule called PB76 which is preferentially expressed by pre-B cells and plasma cells.

Ly-6C is a monocyte/macrophage and endothelial cell differentiation antigen regulated by interferon-gamma

Using a new Ly-6C-specific antibody (Monts-1) we show that this class of antigens are differentially expressed on monocytes/macrophages and endothelial cells. Recently elicited peritoneal exudate Mac-1+ mononuclear cells, as well as Mac-1+ mononuclear cells in the bone marrow and in the peripheral blood, express high levels of Ly-6C. Ly-6C+ mononuclear Mac-1+ cells are absent in normal uninflamed skin, but are present in high numbers in skin lesions 3 days after the s.c. injection of lipopolysaccharide, concanavalin A or complete Freund's adjuvant. In addition, large Ly-6C+ mononuclear cells are predominant in chronic granulomas induced by complete Freund's adjuvant. Resident macrophages in a variety of tissues express low levels or in many cases do not express Ly-6C. Two out of three monocyte-like cell lines are Ly-6C+, whereas macrophage-like cell lines are negative. Ly-6C+ monocytes/macrophages lose the Ly-6C antigen within 24 h after in vitro culture. Ly-6C- cultured monocytes and Ly-6C- monocyte-like cell lines, but not fully differentiated macrophages and macrophage-like cell lines, can be induced to express the Ly-6C antigen by interferon-gamma. A population of small vessel endothelial cells in diverse tissues also express high levels of Ly-6C. The present findings suggest that the Ly-6C antigen family, shown by others to be involved in T cell activation, may have more general importance in immune responses and cellular differentiation than previously appreciated.

Mouse CD1 is distinct from and co-exists with TL in the same thymus

Human CD1 antigens have a similar tissue distribution and overall structure to (mouse) TL. However recent data from human CD1 suggest that the mouse homologue is not TL. Since no human TL has been conclusively demonstrated, we have analysed the murine CD1 genes. Two closely linked genes are found in a tail to tail orientation and the limited polymorphism found shows that, as in humans, the CD1 genes are not linked to the MHC. Both genes are found to be equally transcribed in the thymus, but differentially in other cell types. The expression in liver, especially, does not parallel CD1 in humans. This demonstrates conclusively that CD1 and TL are distinct and can co-exist in the same thymus. It is paradoxical that despite the structural similarity between mouse and human CD1, the tissue distribution of human CD1 is closer to TL. The possibility of a functional convergence between MHC molecules and CD1 is discussed.

B cell progenitors have different growth requirements before and after immunoglobulin heavy chain commitment

Using the clonable pre-B cell assay, we have identified B cell progenitors that are not yet committed to the production of a particular H chain allele. These cells represent approximately 10-20% of clonable pre-B cells found in 15-d fetal liver. The clonable pre-B cell assay provides an environment adequate for the expansion and differentiation of these cells into mature, Ig-secreting, cells. Using the same methodology, we have also identified progenitors that are uncommitted to the production of a particular L chain isotype. Moreover, investigating the growth requirements for clonable pre-B cells has led to the discovery of selective growth conditions that distinguish cells before and after commitment to H chain allotype.