Microbiome Shapes the T Cell Receptor Repertoire among CD4+CD8+ Thymocytes

The microbiome shapes the mature T cell receptor (TCR) repertoire and thereby influences pathogen control. To investigate microbiome influences on T cells at an earlier, immature stage, we compared single-cell TCR transcript sequences between CD4+CD8+ (double-positive) thymocytes from gnotobiotic [E. coli mono-associated (Ec)] and germ-free (GF) mice. Identical TCRβ transcripts (termed repeat, REP) were more often shared between cells of individual Ec mice compared to GF mice (Fishers Exact test, p < 0.0001). Among Ec REPs, a cluster of Vβ genes (Vβ12-1, 12-2, 13-1, and 13-2, termed 12-13) was well represented, whereas 12-13 sequences were not detected among GF REPs (Fishers Exact test, p = 0.046). Vα genes located in the distal region of the TCRα locus were more frequently expressed in Ec mice compared to GF mice, both among REPs and total sequences (Fishers Exact test, p = 0.009). Results illustrate how gut bacteria shape the TCR repertoire, not simply among mature T cells, but among immature CD4+CD8+ thymocytes.

IgD+ age-associated B cells are the progenitors of the main T-independent B cell response to infection that generates protective Ab and can be induced by an inactivated vaccine in the aged

Age-associated B cells (ABC) accumulate with age and are associated with autoimmunity and chronic infection. However, their contributions to acute infection in the aged and their developmental pathways are unclear. We find that the response against influenza A virus infection in aged mice is dominated by a Fas+ GL7- effector B cell population we call infection-induced ABC (iABC). Most iABC express IgM and include antibody-secreting cells in the spleen, lung, and bone marrow. We find that in response to influenza, IgD+ CD21- CD23- ABC are the precursors of iABC and become memory B cells. These IgD+ ABC develop in germ-free mice, so are independent of foreign antigen recognition. The response of ABC to influenza infection, resulting in iABC, is T cell independent and requires both extrinsic TLR7 and TLR9 signals. In response to influenza infection, IgD+ ABC can induce a faster recovery of weight and higher total anti-influenza IgG and IgM titers that can neutralize virus. Immunization with whole inactivated virus also generates iABC in aged mice. Thus, in unimmunized aged mice, whose other B and T cell responses have waned, IgD+ ABC are likely the naive B cells with the potential to become Ab-secreting cells and to provide protection from infection in the aged.

"An Intrinsic Program Determines Key Age-Associated Changes in Adaptive Immunity that Limit Response to Non-Pathogens."

As mice age their adaptive immune system changes dramatically, leading to weakened responses to newly encountered antigens and poor efficacy of vaccines. A shared pattern emerges in the aged, with both CD4 T and B cell responses requiring higher levels of pathogen recognition. Moreover, in aged germ-free mice we find accumulation of the same novel age-associated T and B cell subsets that we and others have previously identified using mice maintained in normal laboratory animal housing conditions, suggesting that their development follows an intrinsic program.

Murine Adherent and Invasive E. coli Induces Chronic Inflammation and Immune Responses in the Small and Large Intestines of Monoassociated IL-10-/- Mice Independent of Long Polar Fimbriae Adhesin A

BACKGROUND

Adherent and invasive Escherichia coli (AIEC) is preferentially associated with ileal Crohn's disease (CD). The role of AIEC in the development of inflammation and its regional tropism is unresolved. The presence of long polar fimbriae (LPF) in 71% of ileal CD AIEC suggests a role for LPF in the tropism and virulence of AIEC. The aim of our study is to determine if AIEC, with or without LpfA, induces intestinal inflammation in monoassociated IL-10-/- mice.

METHODS

We compared murine AIEC strains NC101 (phylogroup B2, LpfA-) and CUMT8 (phylogroup B1, LpfA+), and isogenic mutant CUMT8 lacking lpfA154, with a non-AIEC (E. coli K12), evaluating histologic inflammation, bacterial colonization, mucosal adherence and invasion, and immune activation.

RESULTS

IL-10-/- mice monoassociated with AIEC (either CUMT8, CUMT8:ΔlpfA, or NC101) but not K12 developed diffuse small intestinal and colonic inflammation. There was no difference in the magnitude and distribution of inflammation in mice colonized with CUMT8:ΔlpfA compared with wild-type CUMT8. Bacterial colonization was similar for all E. coli strains. Fluorescence in situ hybridization revealed mucosal adherence and tissue invasion by AIEC but not K12. Production of the cytokines IL-12/23 p40 by the intestinal tissue and IFN-γ and IL-17 by CD4 T cells correlated with inflammation.

CONCLUSIONS

IL-10-/- mice monoassociated with murine AIEC irrespective of LpfA expression developed chronic inflammation accompanied by IL-12/23 p40 production in the small and large intestines and IFN-γ/IL-17 production by CD4 T cells that model the interplay between enteric pathosymbionts, host susceptibility, and enhanced immune responses in people with IBD.

Transient activation of mucosal effector immune responses by resident intestinal bacteria in normal hosts is regulated by interleukin-10 signalling

Interleukin-10 (IL-10) is a key regulator of mucosal homeostasis. In the current study we investigated the early events after monoassociating germ-free (GF) wild-type (WT) mice with an Escherichia coli strain that we isolated previously from the caecal contents of a normal mouse housed under specific pathogen-free conditions. Our results show that interferon-γ (IFN-γ) secreted by mesenteric lymph node (MLN) cells from both IL-10 deficient mice and WT mice, stimulated ex vivo with E. coli lysate, was dramatically higher at day 4 after monoassociation compared with IFN-γ secreted by cells from GF mice without E. coli colonization. Production of IFN-γ rapidly and progressively declined after colonization of WT but not IL-10-deficient mice. The E. coli lysate-stimulated WT MLN cells also produced IL-10 that peaked at day 4 and subsequently declined, but not as precipitously as IFN-γ. WT cells that express CD4, CD8 and NKp46 produced IFN-γ; WT CD4-positive cells and B cells produced IL-10. Recombinant IL-10 added to E. coli-stimulated MLN cell cultures inhibited IFN-γ secretion in a dose-dependent fashion. MLN cells from WT mice treated in vivo with neutralizing anti-IL-10 receptor antibody produced more IFN-γ compared with MLN cells from isotype control antibody-treated mice. These findings show that a resident E. coli that induces chronic colitis in monoassociated IL-10-deficient mice rapidly but transiently activates the effector immune system in normal hosts, in parallel with induction of protective IL-10 produced by B cells and CD4(+) cells that subsequently suppresses this response to mediate mucosal homeostasis.

Molecular detection of bacterial contamination in gnotobiotic rodent units

Gnotobiotic rodents provide an important technique to study the functional roles of commensal bacteria in host physiology and pathophysiology. To ensure sterility, these animals must be screened frequently for contamination. The traditional screening approaches of culturing and Gram staining feces have inherent limitations, as many bacteria are uncultivable and fecal Gram stains are difficult to interpret. Thus, we developed and validated molecular methods to definitively detect and identify contamination in germ-free (GF) and selectively colonized animals. Fresh fecal pellets were collected from rodents housed in GF isolators, spontaneously contaminated ex-GF isolators, selectively colonized isolators and specific pathogen-free (SPF) conditions. DNA isolated from mouse and rat fecal samples was amplified by polymerase chain reaction (PCR) and subjected to quantitative PCR (qPCR) using universal primers that amplify the 16S rRNA gene from all bacterial groups. PCR products were sequenced to identify contaminating bacterial species. Random amplification of polymorphic DNA (RAPD) PCR profiles verified bacterial inoculation of selectively colonized animals. These PCR techniques more accurately detected and identified GF isolator contamination than current standard approaches. These molecular techniques can be utilized to more definitively screen GF and selectively colonized animals for bacterial contamination when Gram stain and/or culture results are un-interpretable or inconsistent.

Enterococcus faecalis metalloprotease compromises epithelial barrier and contributes to intestinal inflammation

BACKGROUND & AIMS

Matrix metalloproteases (MMPs) mediate pathogenesis of chronic intestinal inflammation. We characterized the role of the gelatinase (GelE), a metalloprotease from Enterococcus faecalis, in the development of colitis in mice.

METHODS

Germ-free, interleukin-10-deficient (IL-10(-/-)) mice were monoassociated with the colitogenic E faecalis strain OG1RF and isogenic, GelE-mutant strains. Barrier function was determined by measuring E-cadherin expression, transepithelial electrical resistance (TER), and translocation of permeability markers in colonic epithelial cells and colon segments from IL-10(-/-) and TNF(ΔARE/Wt) mice. GelE specificity was shown with the MMP inhibitor marimastat.

RESULTS

Histologic analysis (score 0-4) of E faecalis monoassociated IL-10(-/-) mice revealed a significant reduction in colonic tissue inflammation in the absence of bacteria-derived GelE. We identified cleavage sites for GelE in the sequence of recombinant mouse E-cadherin, indicating that it might be degraded by GelE. Experiments with Ussing chambers and purified GelE revealed the loss of barrier function and extracellular E-cadherin in mice susceptible to intestinal inflammation (IL-10(-/-) and TNF(ΔARE/Wt) mice) before inflammation developed. Colonic epithelial cells had reduced TER and increased translocation of permeability markers after stimulation with GelE from OG1RF or strains of E faecalis isolated from patients with Crohn's disease and ulcerative colitis.

CONCLUSIONS

The metalloprotease GelE, produced by commensal strains of E faecalis, contributes to development of chronic intestinal inflammation in mice that are susceptible to intestinal inflammation (IL-10(-/-) and TNF(ΔARE/Wt) mice) by impairing epithelial barrier integrity.

Antigen-presenting cell production of IL-10 inhibits T-helper 1 and 17 cell responses and suppresses colitis in mice

BACKGROUND & AIMS

Mice that are deficient in interleukin (IL)-10 develop colitis, mediated by T-helper (Th)1 and Th17 cells, and IL-10-producing regulatory T (Treg) cells suppress colitis, implicating IL-10 in maintaining mucosal homeostasis. We assessed the relative importance of immunoregulatory IL-10 derived from T cells or from antigen presenting cells (APCs) in development of intestinal inflammation.

METHODS

CD4(+) cells from germ-free (GF) or specific pathogen-free (SPF) IL-10(-/-) or wild-type mice were injected into IL-10(-/-), Rag2(-/-) mice or Rag2(-/-) mice that express IL-10. After 6-8 weeks, we evaluated inflammation, spontaneous secretion of cytokines from colonic tissue, and mRNA levels of the transcription factor T-bet and the immunoregulatory cytokine transforming growth factor (TGF)-β. CD4(+) T cells were co-cultured with bacterial lysate-pulsed APCs and assayed for cytokine production, FoxP3 expression, and TGF-β-mediated Smad signaling.

RESULTS

CD4(+) cells from GF or SPF IL-10(-/-) or wild-type mice induced more severe colitis and higher levels of inflammatory cytokines in IL-10(-/-), Rag2(-/-) mice than in IL-10-replete, Rag2(-/-) mice. Co-cultures of IL-10(-/-) or wild-type CD4(+) T cells plus bacterial lysate-pulsed APCs from IL-10(-/-) mice contained more interferon (IFN)-γ, IL-12/23p40, and IL-17 than co-cultures of the same T cells plus APCs from wild-type mice. CD11b(+) APCs were required for these effects. Blocking IL-10 receptors increased production of IFN-γ and IL-12/23p40 whereas exogenous IL-10 suppressed these cytokines. IL-10-producing APCs induced TGF-β-mediated, retinoic acid-dependent, differentiation of FoxP3(+) Treg cells, whereas blocking the retinoic acid receptor, in vitro and in vivo, reduced proportions of FoxP3(+) Treg cells.

CONCLUSIONS

IL-10 produced by APCs regulates homeostatic T-cell responses to commensal bacteria.

Bifidobacterium animalis causes extensive duodenitis and mild colonic inflammation in monoassociated interleukin-10-deficient mice

BACKGROUND

We recently showed that Bifidobacterium animalis is more prevalent within the colons of interleukin (IL)-10-deficient (-/-) mice than in wildtype (WT) animals colonized with the same specific pathogen-free (SPF) fecal contents. Here we tested the ability of this organism to cause T-cell-mediated intestinal inflammation by introducing it into germ-free (GF) IL-10-/- mice.

METHODS

GF IL-10-/- or WT mice were monoassociated with Bifidobacterium animalis subsp. animalis ATCC (American Type Culture Collection, Manassas, VA) 25527(T) or with B. infantis ATCC 15697(T). Inflammation was measured by blinded histologic scores of the duodenum, cecum, and colon and by spontaneous secretion of IL-12/IL-23 p40 from colonic explants. Bacterial antigen-specific CD4(+) mesenteric lymph node (MLN) T-cell recall responses were measured in response to antigen-presenting cells (APC) pulsed with bacterial lysates.

RESULTS

B. animalis caused marked duodenal inflammation and mild colitis in monoassociated IL-10-/- mice, whereas the intestinal tracts of WT animals remained free of inflammation. B. infantis colonization resulted in mild inflammation in the duodena of IL-10-/- mice. CD4(+) MLN T cells from B. animalis monoassociated IL-10-/- mice secreted high levels of IFN-gamma and IL-17 in response to B. animalis lysate. B. animalis equally colonized the different intestinal regions of WT and IL-10-/- mice.

CONCLUSIONS

B. animalis, a traditional probiotic species that is expanded in experimental colitis in this model, induces marked duodenal and mild colonic inflammation and TH1/TH17 immune responses when introduced alone into GF IL-10-/- mice. This suggests a potential pathogenic role for this commensal bacterial species in a susceptible host.

Endogenous antigen presenting cell-derived IL-10 inhibits T lymphocyte responses to commensal enteric bacteria

Interleukin-10 deficient (IL-10-/-) mice develop chronic T cell-mediated colitis when colonized with normal commensal bacteria, but germ-free (GF) IL-10-/- mice remain disease-free. Antigen presenting cells (APC) secrete regulatory cytokines that help determine T lymphocyte activation or tolerance. CD4(+) T cells from the mesenteric lymph nodes of inflamed IL-10-/- mice secrete more IFN-gamma and IL-17 when cultured with cecal bacterial lysate-pulsed splenic APC from IL-10-/- mice than when cultured with normal control APC. GF IL-10-/- APC induce similar IFN-gamma and IL-17 responses; therefore, the functional difference between normal and IL-10 deficient APC is inherent to the lack of IL-10 and not secondary to inflammation. Bacterial lysate-pulsed normal APC cultured with CD4(+) cells from colitic IL-10-/- mice or with exogenous IFN-gamma secrete higher amounts of IL-10 compared to the same APC cultured with naïve T cells. APC enriched for CD11c(+) cells are potent activators of IFN-gamma and IL-17 production by CD4(+) cells from IL-10-/- mice. These APC also produce IL-12/IL-23 p40 and IL-10. Recombinant IL-10 suppressed and anti-IL-10 receptor antibody increased IFN-gamma, IL-17 and IL-12/IL-23 p40 production in bacterial lysate-pulsed APC and plus CD4(+) T cell co-cultures. Taken together, our results show that endogenous IL-10 produced by APC inhibits responses to commensal bacteria and influences the ability of APC to stimulate IFN-gamma-producing effector lymphocytes, which reciprocally, induce IL-10 production by APC. Cytokines produced by APC are an important determinant of pathogenic versus protective mucosal immune responses to colonic bacterial stimulation.

Aberrant innate immune responses in TLR-ligand activated HLA-B27 transgenic rat cells

BACKGROUND

Commensal enteric microbiota initiate and perpetuate immune-mediated colitis in HLA-B27 transgenic (TG) rats but not wildtype (non-TG) littermates. However, the role of the innate immune response to bacterial components has not been established.

METHODS

We examined responses induced by bacterial adjuvants through Toll-like receptor (TLR) and NOD2 signaling in T-cell-depleted splenocytes from HLA-B27 TG rats versus non-TG controls.

RESULTS

We found that various bacterial adjuvants induced TNF production by cells obtained from specific pathogen-free (SPF) and germ-free (GF, sterile) TG and non-TG rats. Peptidoglycan-polysaccharide (PG-PS), lipopolysaccharide (LPS), and CpG DNA motifs stimulated higher levels of TNF production by SPF TG rat spleen cells compared to non-TG cells. CD11b/c cell depletion eliminated PG-PS and LPS-induced TNF and dramatically reduced CpG-stimulated TNF production. Both SPF and GF TG rat spleens contain more cells that express high levels of CD11b/c and show enhanced mRNA expression of TLR-2 and TLR-4 compared to non-TG rat spleens. In contrast, constitutive and bacterial-induced IL-10 production was markedly lower in TG cells compared to non-TG cells of rats from the same SPF or GF housing conditions. Notably, the ratio of TNF to IL-10 produced after TLR ligand activation was significantly higher in TG than non-TG cells.

CONCLUSIONS

HLA-B27 TG rats have an aberrant cell composition, altered functional TLR expression, and an intrinsic defect in IL-10 production in response to TLR ligands, which may result in exaggerated proinflammatory responses to commensal enteric bacteria and uncontrolled inflammation in this colitis model.

Reduced responsiveness of HLA-B27 transgenic rat cells to TGF-beta and IL-10-mediated regulation of IFN-gamma production

BACKGROUND

We have reported that commensal luminal bacterial components induce an active in vitro IFN-gamma response in mesenteric lymph node (MLN) and intestinal cells from specific pathogen-free (SPF) HLA-B27 transgenic (TG) rats with chronic colitis but not in cells from non-diseased SPF non-TG, germ-free (GF) non-TG or GF TG rats.

METHODS

The study examined IL-12 stimulation of MLN IFN-gamma responses to luminal bacteria and regulation of these responses by suppressive cytokines.

RESULTS

Exogenous IL-12 significantly increased the bacterial lysate-induced IFN-gamma response in SPF TG MLN cells, while bacterial lysate and IL-12 synergistically induced IFN-gamma from low baseline levels in cells obtained from both SPF and GF non-TG rats, and in GF TG cells. TGF-beta fully counteracted the effects of IL-12 and bacterial lysate on non-TG cells by almost completely inhibiting IFN-gamma production. In contrast, TG cells were less responsive to TGF-beta-mediated downregulation with a substantial residual IFN-gamma response to IL-12 plus bacterial lysate. Further experiments showed that CD4+/CD25+ cells had no inhibitory effect on the IFN-gamma production and were not required for TGF-beta-mediated suppression. Addition of exogenous IL-10 also partially inhibited IFN-gamma production by non-TG cells but did not affect TG cells. Conversely, exogenous IL-12 preferentially suppressed bacterial lysate-induced TGF-beta and IL-10 production in TG rat cells.

CONCLUSIONS

An attenuated response to regulatory signals leads to uncontrolled potentiated induction of effector IFN-gamma responses to commensal bacteria in HLA-B27 TG rats that spontaneously develop chronic intestinal inflammation.

Dual-association of gnotobiotic IL-10-/- mice with 2 nonpathogenic commensal bacteria induces aggressive pancolitis

BACKGROUND

Monoassociating gnotobiotic IL-10-deficient (-/-) mice with either nonpathogenic Enterococcus faecalis or a nonpathogenic Escherichia coli strain induces T-cell-mediated colitis with different kinetics and anatomical location (E. faecalis: late onset, distal colonic; E. coli: early onset, cecal).

HYPOTHESIS

E. faecalis and E. coli act in an additive manner to induce more aggressive colitis than disease induced by each bacterial species independently.

METHODS

Germ-free (GF) inbred 129S6/SvEv IL-10-/- and wildtype (WT) mice inoculated with nonpathogenic E. faecalis and/or E. coli were killed 3-7 weeks later. Colonic segments were scored histologically for inflammation (0 to 4) or incubated in media overnight to measure spontaneous IL-12/IL-23p40 secretion. Bacterial species were quantified by serial dilution and plated on culture media. Mesenteric lymph node (MLN) CD4(+) cells were stimulated with antigen-presenting cells pulsed with bacterial lysate (E. faecalis, E. coli, Bacteroides vulgatus) or KLH (unrelated antigen control). IFN-gamma and IL-17 levels were measured in the supernatants.

RESULTS

Dual-associated IL-10-/- (but not WT) mice developed mild-to-moderate pancolitis by 3 weeks that progressed to severe distal colonic-predominant pancolitis with reactive atypia and duodenal inflammation by 7 weeks. NF-kappaB was activated in the duodenum and colon in dual-associated IL-10-/- x NF-kappaB(EGFP) mice. The aggressiveness of intestinal inflammation and the degree of antigen-specific CD4(+) cell activation were greater in dual- versus monoassociated IL-10-/- mice.

CONCLUSION

Two commensal bacteria that individually induce phenotypically distinct colitis in gnotobiotic IL-10-/- mice act additively to induce aggressive pancolitis and duodenal inflammation.

Bacterial symbionts induce a FUT2-dependent fucosylated niche on colonic epithelium via ERK and JNK signaling

The intestinal epithelium of the adult gut supports a complex, dynamic microbial ecosystem and expresses highly fucosylated glycans on its surface. Uncolonized gut contains little fucosylated glycan. The transition toward adult colonization, such as during recovery from germ-free status or from antibiotic treatment, increased expression of fucosylated epitopes in the colonic epithelium. This increase in fucosylation is accompanied by induction of fut2 mRNA expression and alpha1,2/3-fucosyltransferase activity. Colonization stimulates ERK and JNK signal transduction pathways, resulting in activation of transcription factors ATF2 and c-Jun, respectively. This increases transcription of fut2 mRNA and expression of alpha1,2/3-fucosyltransferase activity, resulting in a highly fucosylated intestinal mucosa characteristic of the adult mammalian gut. Blocking the ERK and JNK signaling cascade inhibits the ability of colonization to induce elevated fut2 mRNA and fucosyltransferase activity in the mature colon. Thus pioneer-mutualist symbiotic bacteria may utilize the ERK and JNK signaling cascade to induce the high degree of fucosylation characteristic of adult mammalian colon, and we speculate that this fucosylation facilitates colonization by adult microbiota.

CD4(+) T lymphocytes mediate colitis in HLA-B27 transgenic rats monoassociated with nonpathogenic Bacteroides vulgatus

BACKGROUND

HLA-B27/beta2 microglobulin transgenic (TG) rats develop spontaneous colitis when raised under specific pathogen-free (SPF) conditions or after mono-association with Bacteroides vulgatus (B. vulgatus), whereas germ-free TG rats fail to develop intestinal inflammation. SPF HLA-B27 TG rnu/rnu rats, which are congenitally athymic, remain disease free. These results indicate that commensal intestinal bacteria and T cells are both pivotal for the development of colitis in TG rats. However, it is not known if T cells are also required in the induction of colitis by a single bacterial strain. The aim of this study was therefore to investigate the role of T cells in the development of colitis in B. vulgatus-monoassociated HLA-B27 TG rats.

METHODS

HLA-B27 TG rnu/rnu and rnu/+ rats were monoassociated with B. vulgatus for 8-12 weeks. CD4(+) T cells from mesenteric lymph nodes (MLNs) of B. vulgatus-monoassociated rnu/+ TG donor rats were transferred into B. vulgatus-monoassociated rnu/rnu TG recipients.

RESULTS

B. vulgatus-monoassociated rnu/+ rats showed higher histologic inflammatory scores and elevated colonic interferon-gamma mRNA, cecal myeloperoxidase, and cecal IL-1beta levels compared to those in rnu/rnu TG rats that did not contain T cells. After transfer of CD4(+) cells from colitic B. vulgatus-monoassociated rnu/+ TG donor rats, B. vulgatus-monoassociated rnu/rnu TG recipients developed colitis that was accompanied by B. vulgatus-induced IFN-gamma production by MLN cells in vitro and inflammatory parameters similar to rnu/+ TG rats.

CONCLUSIONS

These results implicate CD4(+) T cells in the development of colitis in HLA-B27 TG rats monoassociated with the nonpathogenic bacterial strain B. vulgatus.

Luminal bacterial antigen-specific CD4+ T-cell responses in HLA-B27 transgenic rats with chronic colitis are mediated by both major histocompatibility class II and HLA-B27 molecules

Rats transgenic (TG) for the human major histocompatibility complex (MHC) class I HLA-B27 and beta2-microglobulin genes develop chronic colitis under specific pathogen-free (SPF) but not sterile (germ-free, GF) conditions. We investigated the role of antigen-presenting molecules involved in generating immune responses by CD4+ mesenteric lymph node (MLN) cells from colitic HLA-B27 TG rats to commensal enteric micro-organisms. All TG MLN cells expressed HLA-B27. A higher level of MHC class II was expressed on cells from TG rats, both SPF and GF, compared to non-TG littermates. In contrast, rat MHC class I expression was lower on TG than non-TG cells. Both TG and non-TG antigen presenting cells (APC) pulsed with caecal bacterial antigens induced a marked interferon-gamma (IFN-gamma) response in TG CD4+ T lymphocytes but failed to stimulate non-TG cells. Blocking MHC class II on both TG and non-TG APC dramatically inhibited their ability to induce TG CD4+ T cells to produce IFN-gamma. Blocking HLA-B27 on TG APC similarly inhibited IFN-gamma responses. When the antibodies against MHC class II and HLA-B27 were combined, no APC-dependent IFN-gamma response was detected. These data implicate both native rat MHC class II and TG HLA-B27 in CD4+ MLN T-cell IFN-gamma responses to commensal enteric microflora in this colitis model.

Adoptive transfer of nontransgenic mesenteric lymph node cells induces colitis in athymic HLA-B27 transgenic nude rats

HLA-B27 transgenic (TG) rats develop spontaneous colitis when colonized with intestinal bacteria, whereas athymic nude (rnu/rnu) HLA-B27 TG rats remain disease free. The present study was designed to determine whether or not HLA-B27 expression on T cells is required for development of colitis after transfer of mesenteric lymph node (MLN) cells into rnu/rnu HLA-B27 recipients. Athymic nontransgenic (non-TG) and HLA-B27 TG recipients received MLN cells from either TG or non-TG rnu/+ heterozygous donor rats that contain T cells. HLA-B27 TG rnu/rnu recipients receiving either non-TG or TG MLN cells developed severe colitis and had higher caecal MPO and IL-1beta levels, and their MLN cells produced more IFN-gamma and less IL-10 after in vitro stimulation with caecal bacterial lysate compared to rnu/rnu non-TG recipients that remained disease free after receiving either TG or non-TG cells. Interestingly, proliferating donor TG T cells were detectable one week after adoptive transfer into rnu/rnu TG recipients but not after transfer into non-TG recipients. T cells from either non-TG or TG donors induce colitis in rnu/rnu TG but not in non-TG rats, suggesting that activation of effector T cells by other cell types that express HLA-B27 is pivotal for the pathogenesis of colitis in this model.

Dysregulated luminal bacterial antigen-specific T-cell responses and antigen-presenting cell function in HLA-B27 transgenic rats with chronic colitis

HLA-B27/beta2 microglobulin transgenic (TG) rats spontaneously develop T-cell-mediated colitis when colonized with normal commensal bacteria, but remain disease-free under germ-free conditions. We investigated regulation of in vitro T-cell responses to enteric bacterial components. Bacterial lysates prepared from the caecal contents of specific pathogen-free (SPF) rats stimulated interferon-gamma (IFN-gamma) production by TG but not non-TG mesenteric lymph node (MLN) cells. In contrast, essentially equivalent amounts of interleukin-10 (IL-10) were produced by TG and non-TG cells. However, when cells from MLNs of non-TG rats were cocultured with TG MLN cells, no suppression of IFN-gamma production was noted. Both non-TG and TG antigen-presenting cells (APC) pulsed with caecal bacterial lysate were able to induce IFN-gamma production by TG CD4+ cells, although non-TG APC were more efficient than TG APC. Interestingly, the addition of exogenous IL-10 inhibited non-TG APC but not TG APC stimulation of IFN-gamma production by cocultured TG CD4+ lymphocytes. Conversely, in the presence of exogenous IFN-gamma, production of IL-10 was significantly lower in the supernatants of TG compared to non-TG APC cultures. We conclude that commensal luminal bacterial components induce exaggerated in vitro IFN-gamma responses in HLA-B27 TG T cells, which may in turn inhibit the production of regulatory molecules, such as IL-10. Alterations in the production of IFN-gamma, and in responses to this cytokine, as well as possible resistance of TG cells to suppressive regulation could together contribute to the development of chronic colitis in TG rats.

Variable phenotypes of enterocolitis in interleukin 10-deficient mice monoassociated with two different commensal bacteria

BACKGROUND & AIMS

To explore the hypothesis that selective immune responses to distinct components of the intestinal microflora induce intestinal inflammation, we characterized disease kinetics and bacterial antigen-specific T-cell responses in ex germ-free interleukin 10 -/- and wild-type control mice monoassociated with Enterococcus faecalis , Escherichia coli , or Pseudomonas fluorescens .

METHODS

Colitis was measured by using blinded histological scores and spontaneous interleukin 12 secretion from colonic strip culture supernatants. Interferon gamma secretion was measured from mesenteric or caudal lymph node CD4 + T cells stimulated with bacterial lysate-pulsed antigen-presenting cells. Luminal bacterial concentrations were measured by culture and quantitative polymerase chain reaction.

RESULTS

Escherichia coli induced mild cecal inflammation after 3 weeks of monoassociation in interleukin 10 -/- mice. In contrast, Enterococcus faecalis-monoassociated interleukin 10 -/- mice developed distal colitis at 10-12 weeks that was progressively more severe and associated with duodenal inflammation and obstruction by 30 weeks. Neither bacterial strain induced inflammation in wild-type mice, and germ-free and Pseudomonas fluorescens-monoassociated interleukin 10 -/- mice remained disease free. CD4 + T cells from Enterococcus faecalis- or Escherichia coli-monoassociated interleukin 10 -/- mice selectively produced higher levels of interferon gamma and interleukin 4 when stimulated with antigen-presenting cells pulsed with the bacterial species that induced disease; these immune responses preceded the onset of histological inflammation in Enterococcus faecalis -monoassociated mice. Luminal bacterial concentrations did not explain regional differences in inflammation.

CONCLUSIONS

Different commensal bacterial species selectively initiate immune-mediated intestinal inflammation with distinctly different kinetics and anatomic distribution in the same host.

Reduced ratio of protective versus proinflammatory cytokine responses to commensal bacteria in HLA-B27 transgenic rats

Germ-free HLA-B27 transgenic (TG) rats do not develop colitis, but colonization with specific pathogen-free (SPF) bacteria induces colitis accompanied by immune activation. To study host-dependent immune responses to commensal caecal bacteria we investigated cytokine profiles in mesenteric lymph node (MLN) cells from HLA-B27 TG versus nontransgenic (non-TG) littermates after in vitro stimulation with caecal bacterial lysates (CBL). Supernatants from CBL-stimulated unseparated T- or B- cell-depleted MLN cells from HLA-B27 TG and non-TG littermates were analysed for IFN-gamma, IL-12, TNF, IL-10 and TGF-beta production. Our results show that unfractionated TG MLN cells stimulated with CBL produced more IFN-gamma, IL-12 and TNF than did non-TG MLN cells. In contrast, CBL-stimulated non-TG MLN cells produced more IL-10 and TGF-beta. T cell depletion abolished IFN-gamma and decreased IL-12 production, but did not affect IL-10 and TGF-beta production. Conversely, neither IL-10 nor TGF-beta was produced in cultures of B cell-depleted MLN. In addition, CD4(+) T cells enriched from MLN of HLA-B27 TG but not from non-TG rats produced IFN-gamma when cocultured with CBL-pulsed antigen presenting cells from non-TG rats. Interestingly, IL-10 and TGF-beta, but not IFN-gamma, IL-12 and TNF were produced by MLN cells from germ-free TG rats. These results indicate that the colitis that develops in SPF HLA-B27 TG rats is accompanied by activation of IFN-gamma-producing CD4(+) T cells that respond to commensal bacteria. However, B cell cytokine production in response to components of commensal intestinal microorganisms occurs in the absence of intestinal inflammation.

Lactobacillus plantarum 299V in the treatment and prevention of spontaneous colitis in interleukin-10-deficient mice

Interleukin (IL)-10-deficient (IL-10-/-) mice develop colitis under specific pathogen-free (SPF) conditions and remain disease free if kept sterile (germ free [GF]). We used four different protocols that varied the time-points of oral administration of Lactobacillus plantarum 299v (L. plantarum) relative to colonization with SPF bacteria to determine whether L. plantarum could prevent and treat colitis induced by SPF bacteria in IL-10-/- mice and evaluated the effect of this probiotic organism on mucosal immune activation. Assessment of colitis included blinded histologic scores, measurements of secreted colonic immunoglobulin isotypes, IL-12 (p40 subunit), and interferon (IFN)-gamma production by anti-CD3-stimulated mesenteric lymph node cells. Treating SPF IL-10-/- mice with L. plantarum attenuated previously established colonic inflammation as manifested by decreased mucosal IL-12, IFN-gamma, and immunoglobulin G2a levels. Colonizing GF animals with L. plantarum and SPF flora simultaneously had no protective effects. Gnotobiotic IL-10-/- mice monoassociated with L. plantarum exhibited mild immune system activation but no colitis. Pretreatment of GF mice by colonization with L. plantarum, then exposure to SPF flora and continued probiotic therapy significantly decreased histologic colitis scores. These results demonstrate that L. plantarum can attenuate immune-mediated colitis and suggest a potential therapeutic role for this agent in clinical inflammatory bowel diseases.

Disrupted B-lymphocyte development and survival in interleukin-2-deficient mice

Interleukin-2-deficient (IL-2-/-) mice develop a spontaneous, progressive, CD4+ T-cell-mediated colitis with an age-related decrease in the number of B lymphocytes. The aim of this study was to determine the mechanisms of B-cell loss in IL-2-/- mice. Serum immunoglobulin G1 (IgG1) levels in 8-week-old IL-2-/- mice were above normal but then decreased dramatically with advancing age. Between 8 and 11 weeks of age, the number of B-cell progenitors (B220+ IgM-) in the bone marrow of IL-2-/- mice was less than half of those in IL-2+/+ littermates. By 22 weeks of age, very few progenitor cells remained in the bone marrow of most mice, and spleens were almost devoid of B cells. Likewise, B1 cells were not present in the peritoneal cavity of aged IL-2-/- mice. Flow cytometry analysis of B-cell differentiation in the bone marrow suggested a progressive loss of B cells from the most mature to the least mature stages, which was not dependent on IL-2 receptor-alpha (IL-2Ralpha) expression. B cells transferred from normal animals had similar survival rates in IL-2-/- and wild-type mice. We conclude that conventional B cells in older IL-2-/- mice are lost by attrition owing to a derangement in B-cell development. Because B1 cells are less dependent on the bone marrow, a separate mechanism for their loss is suggested.

Continuous stimulation by normal luminal bacteria is essential for the development and perpetuation of colitis in Tg(epsilon26) mice

BACKGROUND & AIMS

Normal resident bacteria are required for development of colitis in several rodent models. We determined whether bacterial stimulation is necessary for both induction and perpetuation of mucosal inflammation and T-cell activation in Tg(epsilon26) mice, in which transplantation of wild-type bone marrow (BM-->Tg(epsilon26)) causes colitis under specific pathogen-free (SPF) conditions.

METHODS

BM from (C57BL/6 X CBA/J) F1 mice was transplanted into germfree (GF) or SPF Tg(epsilon26) mice. Mesenteric lymph node (MLN) cells from these mice were then transferred into SPF or GF recipients. Colitis and activation of MLN cells were measured by histologic scores, membrane marker analysis, and intracellular cytokine staining. Cytokine secretion by MLN cells stimulated by anti-CD3 or by luminal or epithelial antigens was measured by ELISA.

RESULTS

Colitis did not develop when BM was transferred into GF recipient mice (BM-->GF Tg(epsilon26)). T lymphocytes that secreted interferon gamma upon activation were present in the MLN of BM-->GF Tg(epsilon26) mice, albeit in lower frequency than in control BM-->SPF Tg(epsilon26) mice. Furthermore, transfer of MLN cells from BM-->SPF Tg(epsilon26) mice into SPF Tg(epsilon26) recipients induced active colitis, but not if the same cells were transferred into GF Tg(epsilon26) recipients. Although CD4 T cells were detected in the colonic mucosa of GF recipients, no inflammation was observed for at least 31 weeks. In a reciprocal experiment, MLN cells from BM-->GF Tg(epsilon26) mice without colitis transferred disease to SPF Tg(epsilon26) recipients within 2-4 weeks.

CONCLUSIONS

Activated T cells are present in the mucosa of BM-->GF Tg(epsilon26) mice but are incapable of inducing disease unless colonic bacteria are present. Moreover, pathogenic T cells require the continuous presence of colonic bacteria to sustain colitis.

Natural killer cell-dependent immunoglobulin G2a anti-bovine serum albumin (BSA) response elicited by high molecular weight dextran-BSA conjugates associated with dextran-mediated macrophage-natural killer cell interaction

The roles of the interferon-gamma (IFN-gamma) and interleukin-12 (IL-12) produced during natural killer (NK) cell interaction with macrophages (M phi) were investigated as the basis for the induction of immunoglobulin G2a (IgG2a) anti-bovine serum albumin (BSA) responses by high molecular weight dextran conjugated to BSA (HMW-DEX-BSA). BALB/c mice immunized with HMW-DEX-BSA produced significantly higher levels of both IgG1 and IgG2a anti-BSA than did mice immunized with BSA alone. Both IgG1 and IgG2a anti-BSA levels were higher in mice immunized with BSA conjugated to dextran of molecular weight (MW) 5 000 000-40 000 000 compared with dextran of MW 10,000-60,000. The enhancement of anti-BSA IgG2a levels but not of anti-BSA IgG1 levels was inhibited when free BSA was added to the HMW-DEX-BSA conjugate. NK cell depletion during HMW-DEX-BSA immunization of mice resulted in significantly lower anti-BSA IgG2a levels without affecting anti-BSA IgG1 levels. Naive splenocytes or M phi + NK cell co-cultures incubated with HMW-DEX or HMW-DEX-BSA produced higher IFN-gamma levels than splenocytes or co-cultures incubated with BSA alone. HMW-DEX stimulated both IFN-gamma and IL-12 production by M phi + NK cell co-cultures in a dose-dependent manner. DEX-induced IFN-gamma production by NK cells was dependent upon the presence of IL-12, and IL-12 production by M phi was dependent upon the presence of IFN-gamma in these co-cultures. Both M phi and NK cells bound DEX to their surfaces. These data demonstrate that BSA linked to HMW-DEX enhanced both T-helper-1- and T-helper-2-associated antibody responses to BSA. The results also indicate an IL-12-dependent positive feedback interaction between NK cells and M phi that supports a NK cell/IFN-gamma-dependent mechanism for enhancement of anti-BSA IgG2a antibody responses in mice immunized with HMW-DEX-BSA protein conjugates.

Helicobacter hepaticus does not induce or potentiate colitis in interleukin-10-deficient mice

Helicobacter hepaticus has been reported to induce colitis, hepatitis, and hepatocellular carcinoma in several different murine models. The aim of this study was to determine if H. hepaticus will cause colitis in monoassociated mice lacking the interleukin-10 gene (IL-10(-/-) mice) and potentiate colitis in specific-pathogen-free (SPF) IL-10(-/-) mice. Germfree IL-10(-/-) mice on either a mixed (C57BL/6 x 129/Ola) or inbred (129/SvEv) genetic background were monoassociated with H. hepaticus ATCC 51448 by oral feeding and rectal enemas. In a second experiment, germfree IL-10(-/-) mice were colonized with stool from SPF mice that harbored or did not harbor endogenous H. hepaticus. After 7 to 9 weeks of colonization, weight loss and mortality were assessed, the colon was isolated for histology and IL-12 secretion, and mesenteric lymph node cells were assessed for T-cell activation markers. It was found that IL-10(-/-) mice monoassociated with H. hepaticus for up to 16 weeks showed almost no histologic colitis or increased IL-12 production. SPF IL-10-knockout mice had no significant difference in weight loss, mortality rate, histologic scores, colonic IL-12 secretion, or T-cell activation with or without H. hepaticus. We conclude that H. hepaticus does not induce or potentiate disease in our IL-10(-/-) mice and therefore is not required to induce colitis in genetically susceptible hosts.

Interleukin 2, but not other common gamma chain-binding cytokines, can reverse the defect in generation of CD4 effector T cells from naive T cells of aged mice

Development of effectors from naive CD4 cells occurs in two stages. The early stage involves activation and limited proliferation in response to T cell receptor (TCR) stimulation by antigen and costimulatory antigen presenting cells, whereas the later stage involves proliferation and differentiation in response to growth factors. Using a TCR-transgenic (Tg(+)) model, we have examined the effect of aging on effector generation and studied the ability of gamma(c) signaling cytokines to reverse this effect. Our results indicate that responding naive CD4 cells from aged mice, compared with cells from young mice, make less interleukin (IL)-2, expand poorly between days 3 to 5, and give rise to fewer effectors with a less activated phenotype and reduced ability to produce cytokines. When exogenous IL-2 or other gamma(c) signaling cytokines are added during effector generation, the Tg(+) cells from both young and aged mice proliferate vigorously. However, IL-4, IL-7, and IL-15 all fail to restore efficient effector production. Only effectors from aged mice generated in the presence of IL-2 are able to produce IL-2 in amounts equivalent to those produced by effectors generated from young mice, suggesting that the effect of aging on IL-2 production is reversible only in the presence of exogenous IL-2.

IL-2-deficient mice raised under germfree conditions develop delayed mild focal intestinal inflammation

Interleukin-2 (IL-2) amplifies immune stimuli and influences B cell differentiation. IL-2-deficient mice spontaneously develop intestinal inflammation if raised under specific pathogen-free (SPF) conditions. We quantitatively determined the aggressiveness and kinetics of gastrointestinal and hepatic inflammation in the presence or absence of viable bacteria in IL-2-deficient mice. Breeding colonies were maintained under SPF and germfree (GF) conditions. Intestinal tissues, serum, and mesenteric lymph nodes were obtained from mice at different ages for blind histological scoring, immunoglobulin measurements, mucosal T cell infiltration, and cytokine secretion. GF IL-2 -/- mice developed mild, focal, and nonlethal intestinal inflammation with delayed onset, whereas the more aggressive inflammation in SPF IL-2 -/- mice led to their death between 28 and 32 wk. Periportal hepatic inflammation was equal in the presence or absence of bacterial colonization. Intestinal immunoglobulin secretion decreased significantly by 13 wk of age in IL-2 -/- mice in both GF and SPF environments. In contrast to other genetically engineered rodents, IL-2 -/- mice develop mild focal gastrointestinal and active portal tract inflammation in the absence of viable bacteria.

Blockade of both L-selectin and alpha4 integrins abrogates naive CD4 cell trafficking and responses in gut-associated lymphoid organs

The recirculation of naive lymphocytes from blood to lymph that is initiated in high endothelial venules (HEV) of secondary lymphoid organs such as lymph nodes and Peyer's patches (PP) is regulated by multiple interactions of adhesion receptor/counter-receptor pairs involving both selectins and integrins. We showed previously that blocking of only L-selectin is sufficient to ablate trafficking of naive CD4 cells and the development of their responses in peripheral lymph nodes but not in PP where alpha4beta7 integrins are thought to primarily regulate entry. However, although antibody to alpha4 integrins partially inhibited homing of naive CD4 cells to PP and not to lymph nodes, there was no effect on the development primary responses in these tissues or spleens. Since previous studies indicate that both alpha4beta7 integrins and L-selectin regulate adhesion of naive cells to PP HEV, we examined the effect a blockade of both adhesion pathways on the recirculation of naive CD4 cells. There was no detectable homing of naive CD4 cells to PP or lymph nodes when interactions with both receptors were inhibited, resulting in a profound depletion of naive CD4 cells and loss of antigen responses in these sites. In contrast, increased numbers of naive CD4 cells and responses of higher magnitude were found in the spleen. The results demonstrate recirculation of naive CD4 cells through tissues where entry is controlled through HEV is essential for the local generation of primary responses.

Sensitized liposomes as an antigen delivery system for the stimulation of mucosal immunity

This study was designed to exploit the ability of Peyer's patch M cells to recognize antigen-antibody complexes in the targeted delivery of a model antigen for the induction of mucosal immunity. Sensitized liposomes consisted of an entrapped model antigen, ovalbumin (OVA), and coated with unrelated antigen-antibody complexes. Sensitized liposomes were administered intrajejunally to mice either with or without monophosphoryl lipid A (MLA). Humoral immune responses were monitored in saliva, feces, serum, and bile. Mice which received sensitized liposomes showed up to 4-fold amounts of specific IgA in saliva, feces, and bile compared to controls. Transient increases in anti-OVA IgA and IgG were observed in serum. Formulations including MLA generated positive anti-OVA IgG responses in both serum and bile. In separate experiments, cell proliferation studies were performed with Peyer's patch lymphocytes harvested from mice immunized with OVA in either standard or sensitized liposomes. Lymphocytes from test mice receiving only sensitized liposomes proliferated in the presence of OVA, but not an unrelated antigen. Taken together, these results support the potential application of antigen-antibody complexes in the stimulation of mucosal immune responses and that MLA may play an important role in overcoming OVA tolerogenicity.

L-selectin is not essential for naive CD4 cell trafficking or development of primary responses in Peyer's patches

We showed previously that L-selectin-dependent recirculation of naive CD4 cells is essential for development of primary responses in peripheral lymph nodes. Recent studies suggest that L-selectin is also required for lymphocyte entry into gut mucosal lymphoid tissues that include Peyer's patches and mesenteric lymph nodes. Here we show that anti-L-selectin antibody, MEL-14, inhibited homing of a rigorously purified, homogenous population of naive CD4 cells into both of these tissues as well as peripheral lymph nodes, directly demonstrating a role for this receptor in regulating entry into gut-associated sites. However, in intact animals, treatment with MEL-14 resulted in the loss of naive CD4 cells (CD45RBhi, CD44lo from peripheral lymph nodes but not Peyer's patches, whereas mesenteric lymph nodes were intermediate in this regard. In mice primed by parenteral immunization with keyhole limpet hemocyanin (KLH), primary CD4 responses were readily detected in both. Peyer's patches and mesenteric lymph nodes, and were not affected by exposure to MEL-14. Indeed, similar frequencies of KLH-specific CD4 cells were recovered from both of these tissues irrespective of MEL-14 treatment. The results indicate that interactions with L-selectin can be circumvented to allow entry of naive CD4 cells into Peyer's patches but not peripheral lymph nodes.

Distinct lymphokine production by CD4+ T cells isolated from mucosal and systemic lymphoid organs

We have investigated the potential of CD4+ T cells isolated from Peyer's patches and mesenteric lymph nodes (mucosa-associated lymphoid tissues) and from spleens and peripheral lymph nodes (systemic lymphoid tissues) to secrete a variety of lymphokines. The results show several pronounced differences in the kinetics of lymphokine production and in the levels of lymphokines detected after primary and secondary in vitro stimulation with immobilized anti-CD3. The most striking difference was seen in the production of interleukin-4 (IL-4). Supernatants of splenic CD4-bearing cells collected at early time-points after primary stimulation contained high levels of IL-4. Supernatants of Peyer's patch and mesenteric lymph node CD4+ T cells contained considerably lower levels of IL-4 at all time-points analysed, while supernatants of peripheral lymph node CD4+ T cells contained high levels of IL-4, but only at late time-points. Neither cell concentration nor availability of accessory cells appeared to account for the differences observed in IL-4 production by the CD4+ T cells studied. Splenic CD4+ T cells most rapidly and effectively used the IL-4 they produced, as determined by analysing IL-4 production after restimulation. Therefore, we conclude that the spleen is a more potent source of IL-4 than are the mucosa-associated lymphoid tissues studied here. Amounts of IL-2, IL-3, IL-5, and IL-6 were similar in supernatants of all of the CD4+ T cells studied. Peyer's patch CD4+ T-cell supernatants contained the lowest levels of interferon-gamma and peripheral lymph node supernatants displayed the highest accumulation of this lymphokine.

Regulation of isotype production by IL-4 and IL-5. Effects of lymphokines on Ig production depend on the state of activation of the responding B cells

The effects of IL-4 and IL-5 on the production of Ig of different isotypes was investigated. We compared B cells from spleen and from Peyer's patches either stimulated with LPS or without added polyclonal stimulation. We also compared high density (small) and low density (large) B cells. The effect of lymphokines depended on the size and source of the B cells as well as on whether LPS was added. As expected, small B cells from either lymphoid compartment responded to LPS alone and IL-4 suppressed IgM and IgG3 production and enhanced IgG1. In contrast, when large B cells were examined, the suppressive effects of IL-4 were much less apparent but the enhancement of IgG1 was still marked. IL-5 alone had only minimal effects in LPS-stimulated cultures but the combination of IL-4 plus IL-5 appeared to overcome much of the IL-4-mediated suppression of IgM, and IgA production was enhanced. In the absence of LPS, a quite different profile is seen. First, small B cells make little if any response. Second, there is dramatic synergy between IL-4 and IL-5 in the response of large B cells, which is independent of isotype. Third, IL-4 does not suppress any isotype in the absence of LPS. Fourth, IL-4 plus IL-5 stimulate large Peyer's patch B cells to produce 10 times more IgA but three times less IgM than large spleen B cells. Fifth, Th2 cells directly stimulate both large and small B cells.

Regulation of isotype production by IL-4 and IL-5. Effects of lymphokines on Ig production depend on the state of activation of the responding B cells

The effects of IL-4 and IL-5 on the production of Ig of different isotypes was investigated. We compared B cells from spleen and from Peyer's patches either stimulated with LPS or without added polyclonal stimulation. We also compared high density (small) and low density (large) B cells. The effect of lymphokines depended on the size and source of the B cells as well as on whether LPS was added. As expected, small B cells from either lymphoid compartment responded to LPS alone and IL-4 suppressed IgM and IgG3 production and enhanced IgG1. In contrast, when large B cells were examined, the suppressive effects of IL-4 were much less apparent but the enhancement of IgG1 was still marked. IL-5 alone had only minimal effects in LPS-stimulated cultures but the combination of IL-4 plus IL-5 appeared to overcome much of the IL-4-mediated suppression of IgM, and IgA production was enhanced. In the absence of LPS, a quite different profile is seen. First, small B cells make little if any response. Second, there is dramatic synergy between IL-4 and IL-5 in the response of large B cells, which is independent of isotype. Third, IL-4 does not suppress any isotype in the absence of LPS. Fourth, IL-4 plus IL-5 stimulate large Peyer's patch B cells to produce 10 times more IgA but three times less IgM than large spleen B cells. Fifth, Th2 cells directly stimulate both large and small B cells.

Stimulation of gut-associated lymphoid cells by IL-4 and B-cell growth factor II

We have analysed the ability of B cells isolated from the Peyer's patches of normal mice to respond to two different B-cell stimulatory factors. Peyer's patch B cells respond in vitro to co-stimulation by either interleukin-4 (IL-4) plus anti-IgM or B-cell growth factor II (BCGF-II) plus dextran sulphate (DXS). We have consistently observed that splenic B cells proliferate more than Peyer's patch B cells when co-stimulated by BCGF-II plus DXS. This is not due to a diminished proliferation capacity of the Peyer's patch B-cell preparations, because the Peyer's patch B cells often proliferate more than splenic B cells when co-stimulated with IL-4 plus anti-IgM. These differences are not a result of altered response kinetics or differences in relative amounts of surface IgM on the two types of B cells. We have also analysed B cells from the LPS hypo-responsive strain C3H/HeJ, and its LPS responsive partner strain C3H/OuJ, from the X-linked immunodeficient strain (xid), CBA/N, and from germ-free (GF) mice. B cells from spleens and Peyer's patches of GF mice are responsive to co-stimulation by IL-4 plus anti-IgM and to co-stimulation by BCGF-II plus DXS. Peyer's patch B cells from C3H/HeJ mice proliferate as well as Peyer's patch B cells from C3H/OuJ cells to both co-stimulation protocols. Among the types of B cells studied here, only cells from spleens and Peyer's patches of mice that bear the xid defect fail to respond to the signals delivered by lymphokine co-stimulation. Our results suggest that while Peyer's patch B cells are stimulated by these two lymphokines, Peyer's patches contain cells that react differently from spleen cells to either the lymphokines IL-4 and BCGF-II, or the co-stimulators anti-IgM or dextran sulphate.

A method for the accurate determination of the specificity of monoclonal antibodies reactive with porcine immunoglobulins

Monoclonal antibodies against porcine IgG were produced by fusion and characterized. The supernatants of microtiter wells containing fusion hybrids were first screened with an ELISA using semi-purified porcine IgG as antigen. Hybrids reactive in ELISA were cloned by limiting dilution. Further characterization of the specificity of the monoclonal antibodies was done by a combination of two methods: SDS-PAGE electroimmunoblotting and convection blotting of immunoelectrophoretic patterns (IEP-immunoblotting). Using these techniques, we identified monoclonal antibodies specific for porcine Ig gamma chains.

Analysis of the B10.D2-H-2dml mutant with monoclonal antibodies

We compared H-2D products of B10.D2 and the mutant B10.D2-H-2dml spleen cells using two monoclonal antibodies designated D3.179 and S11.7. D3.179 reacts with public specificities and appears to define more than one product as shown by cytotoxicity and binding studies. Strong reactivity was obtained in both binding and cytotoxicity to B10.D2 and marginal cytotoxicity and low binding were observed with B10.D2-H-2dml cells. The second monoclonal antibody S11.7, in contrast, reacts only with H-2Dd bearing strains and gave strong binding to B10.D2-H-2dml and weaker binding to B10.D2. Taken together, the observations indicate that the mutant not only expresses H-2D encoded antigens but bears quantitatively greater amounts of some specificities than the parent. A product of approximately 46,000 daltons was immunoprecipitated from B10.D2 cells by D3.179. Very small amounts of this product were seen in B10.D2-H-2dml immunoprecipitates.

Paired H-2-specific monoclonal antibodies react differently to red cells and lymphocytes

Two hybrid clones from a fusion of C57BL/6 anti-DBA/2 spleen cells and the myeloma line Sp2/0 secrete antibodies reactive with a product of the murine major histocompatibility complex (MHC). The two antibodies are provisionally designated S13.11 and S13.29. Both react in rabbit-complement-mediated cytotoxicity with spleen cells of H-2d, H-2f, H-2r, and H-2p strains. In addition, both antibodies hemagglutinate red blood cells from these strains. S13.11 is also cytotoxic for H-2a, H-2k, H-2u, and H-2v spleen cells but does not hemagglutinate red blood cells from mice bearing these haplotypes. With the exception of H-2v, this strain pattern mimics the public specificity H-28. Quantitative absorption of S13.11 shows that H-2d cells are twice as efficient as H-2k cells in their ability to remove the S13.11 antibody. S13.29 reacts weakly in cytotoxicity with H-2k spleen cells and does not react with cells from H-2u or H-2v. Blocking studies indicate that S13.11 and S13.29 react with the same or a closely related molecule on the cell surface.

A New Alloantigenic System Associated with the Mls Locus in the Mouse

An antiserum prepared by injecting C3H/HeJ mice with CBA/J tissues has been shown to react with cell surface components that are not part of any previously described system of serologically detectable alloantigens. The antiserum, which is designated AST-101, acts selectively in cytotoxic tests carried out with lymphoid cells, killing B cells, but not T cells. Phagocytic cells found in peritoneal exudates are also killed by AST-101 and complement in vitro; the sensitivity of other cell types has not been determined. Strain distribution does not indicate any association of the AST-101 system with H-2, Ly, or Thy systems; genetic analysis reveals close linkage with the mouse minor MLC-stimulating (Mls) locus. Serologic analysis also points to a close association between antigens reactive with AST-101 and the products of the Mls genes.

A new alloantigenic system associated with the Mls locus in the mouse

An antiserum prepared by injecting C3H/HeJ mice with CBA/J tissue has been shown to react with cell surface components that are not part of any previously described system of serologically detectable alloantigens. The antiserum, which is designated AST-101, acts selectively in cytotoxic tests carried out with lymphoid cells, killing B cells, but not T cells. Phagocytic cells found in peritoneal exudates are also killed by AST-101 and complement in vitro; the sensitivity of other cell types has not been determined. Strain distribution does not indicate any association of the AST-101 system with H-2, Ly, or Thy systems; genetic analysis reveals close linkage with the mouse minor MLC-stimulating (Mls) locus. Serologic analysis also points to a close association between antigens reactive with AST-101 and the products of the Mls genes.