Regulation of mucosal IgA production in vitro by autoreactive immunoregulatory T cells from murine Peyer's patches

Interleukin-6-deficient mice refractory to IgA dysregulation but not anorexia induction by vomitoxin (deoxynivalenol) ingestion

Dietary exposure to the trichothecene vomitoxin (VT) causes feed refusal and elevates IgA production in the mouse. Based on the observations that IL-6 can cause anorexia and promote IgA production and that gene expression of this cytokine is increased in vivo and ex vivo on VT exposure, we hypothesized that IL-6 is an essential cytokine in VT-induced feed refusal and IgA dysregulation. To test this hypothesis, the effects of dietary VT on feed intake, weight gain, serum IgA levels and kidney mesangial IgA deposition in an IL-6-"knockout" mouse (B6129-IL6(tmi Kopf)) were compared to those in both a corresponding "wildtype" (B6129F2) and a previously characterized "sentinel" strain (B6C3F1) that possess the intact gene for this cytokine. IL-6 deficiency did not alter the capacity of VT to cause feed refusal or impair weight gain. VT-fed B6129F2 and B6C3F1 mice had significantly higher serum IgA concentrations than did their corresponding controls fed clean diet, whereas significant differences were not observed between IL-6 KO mice fed VT or control diets. Kidneys taken from VT-fed wild-type and sentinel mice had significantly increased mesangial IgA deposition as compared to controls. While slight increases in mesangial IgA were observed in VT-fed IL-6 KO mice, mean fluorescence intensities were significantly less than that found in the corresponding wild-type and sentinel strains. IL-6 KO mice appeared to be less prone to the development of microscopic haematuria following VT exposure than were the corresponding wild-type and sentinel strains. In total, the results suggested that IL-6-deficient mice were refractory to VT-induced dysregulation of IgA production and development of IgA nephropathy, whereas chronic VT-mediated nutritional effects related to feed intake and weight gain were unaffected.

Potential role for IL-5 and IL-6 in enhanced IgA secretion by Peyer's patch cells isolated from mice acutely exposed to vomitoxin

Dietary exposure to vomitoxin (VT) results in hyperelevated serum IgA and IgA nephropathy in mice. To assess the possible role of cytokines in this IgA dysregulation, the effects of a single oral exposure in B6C3F1 male mice to 0, 5 or 25 mg/kg BW VT on production of IgA and cytokines in Peyer's patch (PP) and spleen cell cultures were evaluated. IgA levels were increased significantly in PP cell cultures prepared from mice at 2 or 24 h after oral exposure to VT and subsequently stimulated with phorbol myristate acetate (PMA) and ionomycin (ION) or with lipopolysaccharide (LPS). Significant effects on IgA production were not observed in spleen cell cultures. Since cytokines such as IL-2, IL-4, IL-5 and IL-6 have been shown to promote IgA production, the effect of the same VT exposure regimen on secretion of these mediators was determined in PP and spleen cultures. Supernatant IL-2 and IL-4 levels were unaffected by the prior treatment of animals with VT. In contrast, IL-5 levels were increased significantly in 7-day PP cell cultures obtained 2 h after VT exposure both with and without PMA + ION exposure but not in other cultures. IL-6 levels were increased significantly in LPS-treated cultures prepared from PP at 2 and 24 h following exposure to VT. IL-6 levels were also elevated significantly in both PMA + ION or LPS treated cultures from spleen isolated at 2 h but not 24 h post VT exposure. To determine whether IL-5 or IL-6 play a role in IgA hyperelevation in vitro, PP and spleen cells from mice obtained 2 h after exposure to 25 mg/kg VT were cultured in the presence of neutralizing cytokine antibodies (Abs) and IgA production was monitored. Consistent with IL-5's previously documented role in IgA production, anti-IL-5 decreased IgA levels to background in cultures of both control and VT-exposed PP or spleen cells in the presence of either PMA + ION or LPS. Similar results were seen with addition of anti-IL-6. IgA levels were decreased to a lesser extent in PP cells cultured with LPS and in spleen cells cultured with PMA + ION from VT-exposed mice to which anti-IL-2 Ab was added. Thus, the potential for enhanced IgA production exists in lymphocytes as early as 2 h and as late as 24 h after a single oral exposure to VT and this may be related to the increased capacity to secrete helper cytokines of T cell and macrophage origin. Taken together, the results suggest that the superinduction of cytokine expression may, in part, be responsible for upregulation of IgA secretion in mice exposed orally to VT.

Induction of IgA B cell differentiation of bone marrow-derived B cells by Peyer's patch autoreactive helper T cells

The objective of this study was to demonstrate in vitro that bone marrow-derived pro/pre-B cells bearing mu mRNA can switch their Ig heavy-chain isotype to that of alpha mRNA-expressing B cells after contact with Peyer's patches-derived activated autoreactive CD4+ T cells. Bone marrow-derived pro/pre-B cells and activated autoreactive Peyer's patch, mesenteric lymph node, or spleen CD4+ T cells were co-cultured in the presence of recombinant (r) IL-2, rIL-7, and Con A for 3 days. The mixed cultured cells were isolated for preparation of total RNA. Dot/slot hybridization, using murine C mu (pu3741) and C alpha (P alpha J558) Ig heavy-chain cDNA probes, detected C mu and C alpha Ig heavy-chain mRNA transcripts. The magnitude of each mRNA expression was measured demsitometrically. In addition, the secreted class-specific Ig contents from the co-cultured supernatants were measured. The results indicate that activated autoreactive Peyer's patch and mesenteric lymph node CD4+ T cells provide a specific Ig heavy-chain switch from mu to alpha (Peyer's patch CD4+ T cells > mesenteric lymph node CD4+ T cells) in bone marrow-derived pro/pre-B cells and also assist to develop IgA-secreting plasma cells. The alpha heavy-chain switch and IgA production do not occur in the presence of activated autoreactive spleen CD4+ T cells. These results support the view that autoreactive gut Peyer's patch CD4+ T cells, at least, regulate IgA B cell heavy-chain switching and terminal differentiation during gut mucosal B cell development.

Production of IL2 and IL3 in syngeneic mixed lymphocyte reactions of BALB/c mice are elevated during a period of moderate dietary protein deficiency

The mixed lymphocyte reaction (MLR) is a model of T cell responsiveness to antigenic peptides complexed with major histocompatibility (MHC) proteins on antigen presenting cells (APC). Since dietary protein deficiencies alter T cell development, syngeneic and allogeneic MLR were investigated in mice fed a low protein 4% casein (4Ca) or control 20% casein (20Ca) diet. Proliferation of splenic lymphocyte populations from BALB/c mice fed 4Ca was increased during syngeneic and allogeneic MLR compared with lymphocytes from mice fed 20Ca. Increased proliferation was accompanied by significantly higher production of IL2 and IL3 during syngeneic, but not allogeneic MLR. To determine the influence of autologous B cells on IL2 and IL3 production during MLR, lymphocyte populations of mice fed 4Ca or 20Ca were depleted of B cells. Splenic lymphocyte populations of mice fed 4Ca that were depleted of B cells did not exhibit increased IL2 or IL3 production during syngeneic or allogeneic MLR. Splenic APc of mice given 4Ca caused greater proliferation during MLR. However, APC of 4Ca mice did not cause greater IL2 or IL3 production. Similarly neither IgM-B cells nor macrophage from mice fed 4Ca induced elevated IL2 or IL3 production during syngeneic or allogeneic MLR. A dichotomy appeared in that 4Ca-APC were able to induce higher T cell proliferation but not cytokine production compared with 20Ca-APC. The enhancement of T cell responsiveness to Class II MHC determinants on APC during moderate protein deficiency appears to require both T and B cells from mice fed the deficient diet.

Activation of calcium (Ca)-dependent protein kinase C in aged mesenteric lymph node T and B cells

We studied the effects of aging on the activities and translocation of Ca-dependent protein kinase C (PKC) in resting mesenteric lymph node (MLN) T and B cells during the activation process induced by T and B cell mitogens and B cell-stimulatory interleukins, including IL-4, IL-5 and IL-6. The activation process in senescent, resting (high density (HD)) MLN T cells is impaired, when these cells are stimulated with T cell mitogen, Con A. The defect in activation is associated with a reduction in both the new production of inositol-1,4,5-triphosphate (IP3) (an indicator for the production of intracellular free Ca) and the induction of Ca-dependent PKC. In contrast, the activation of the aged B cells with LPS plus/minus interleukins (IL-4, IL-5 and IL-6) is not impaired, being at least associated with a Ca-independent pathway of PKC activation. The elevated IP3 content and total (cytosol plus membrane) PKC activity in both resting T and B cells from aged MLN along with the greater difference in T cells than in B cells suggest that the in vivo Go cell cycle status of these cells may differ from that of the young, involving more in T cells. Finally, the MLN and splenic T cell Ca-dependent and B cell Ca-independent PKC activation do not differ between both age groups.

IL4, IL5 and IL6-mediated regulation of immunoglobulin (Ig) heavy chain class switching and Ig production by gut-associated lymphoid tissue (GALT) B cells from athymic nude (nu/nu) mice

Gut mucosal immunoglobulin (Ig) isotype expression and secretion are known to be regulated by B cell-stimulatory factors (BSF), lymphokines or cytokines from T and non-B cells. The class and amount of Ig secreted appear to depend on the presence of a combination of these factors. The effects of IL-4 and IL-5 on Ig class switching by gut mucosal B cells remain controversial. To shed further light on this issue, young (1-2 months old) athymic nu/nu murine GALT B cells were chosen, because the possibility of in vivo effects of T cells on B cells (in particular at the levels of transcription and translation without changes in surface Ig phenotype expression) cannot be excluded. The results are summarized below. IL-4, IL-5 and IL-6 alone or in combination do not act as IgA heavy chain switch cofactors, but IL-5 and IL-6 do act at least as B cell terminal differentiation factors for any isotype-specific gut-associated lymphoid tissue (GALT) (mesenteric lymph node) B cells in the presence or absence of LPS. The BSF have augmenting effects on class-specific Ig production by GALT sIgM-bearing B cells, when these are treated with the BSF alone. IL-4 alone or in combination with other BSF prevents LPS-stimulated IgM production. BSF without LPS do not evoke production of significant amounts of IgG and IgA by high density (HD) and low density (LD) sIgM-bearing B cells; IgM is synthesized only in small amounts of LD sIgM-bearing B cells in the presence of IL-5 and/or IL-6. There is no difference in the responsiveness of GALT and spleen sIgM-bearing B cells to the BSF.

Correction of antigen-specific T cell defects in aged murine gut-associated lymphoid tissues an immune intervention by combined adoptive transfer of an antigen-specific immunoregulatory CD4 T cell subset and interleukin 2 administration

Gut-associated lymphoid tissues (GALT) from aged mice enterically immunized with Mycobacterium paratuberculosis protoplasmic antigen show hyperreactive humoral immune responses; this hyperresponsiveness can be corrected to a considerable extent, but not entirely, by systemic administration of interleukin 2 (IL 2) alone. The aim of the present study was to determine further whether the hyperreactivity in the antigen-specific humoral immune responses in aged GALT could be fully restored by adoptive transfer of in vitro expanded antigen-specific IL 2-dependent helper (CD4+VV-) T cells from GALT in conjunction with recombinant IL 2 administration. The results show that the age-associated hyperresponsiveness in gut mucosal antigen-specific humoral immune responses can be entirely corrected by adoptive transfer with the antigen-specific GALT T helper cells together with in vivo IL 2 administration. The mechanism of this restoration involves reversal of the decline in antigen-specific CD8+ suppressor T cell functions in aged GALT.

The effects of Peyer's patches inactivation in the rat on the development of antibody-forming cells to intestinal antigen

The effects of Peyer's patch (PP) inactivation on local and systemic immune response in rats was investigated. A cauterization method has been developed to inactivate PP. Animals were primed intraperitoneally or intragastrically with trinitrophenyl-keyhole limpet haemocyanin (TNP-KLH) one day before cauterization, and were challenged intraintestinally two weeks later. The secondary immune response in the spleen, mesenteric lymph node (MLN) and intestinal villi was studied by immunohistochemistry. Histological observations on PP after inactivation showed that most T cells in the interfollicular area had disappeared, as had B cells in the follicle. T cells repopulated PP much slower than B cells. Complete recovery of PP occurred no earlier than 2 weeks after inactivation. The immunization experiments revealed higher numbers of anti-TNP antibody-forming cells (anti-TNP AFC) of IgM, IgG and IgA isotypes in the spleen of the PP-inactivated animals than in the controls. Very few anti-TNP AFC were found locally in the lamina propria of the intestinal villi or in the MLN in both groups. It is suggested that PP play a role in the regulation of systemic immune responses against intestinally-administered thymus-dependent antigen. Moreover, inactivation of PP could alter the antigen uptake by gut epithelium and the local antigen processing. As a result, an increased amount of antigen could reach the spleen eliciting a higher immune response.