Primary antigen-specific T-cell proliferative responses following presentation of soluble protein antigen by cells from the murine small intestine.

To understand the local immune events which occur when a novel antigen is encountered in the gut it is necessary to know whether cells from the mucosal tissues are capable of initiating T-cell reactivity. We have examined the capacity of cells isolated from the Peyer's patches and the lamina propria of the murine small intestine to present keyhole limpet haemocyanin (KLH) to naive syngeneic splenic T cells in vitro. The properties of the gut antigen-presenting cells (APC) were compared with those of cells from the spleen and the mesenteric lymph nodes. Results clearly demonstrate that cells from the lamina propria as well as from the Peyer's patches, mesenteric lymph node and spleen can present KLH to naive T cells, inducing strong proliferative reactions comparable in magnitude and kinetics. All the APC populations tested induced interleukin-2 (IL-2) production in primary cultures, although minor differences were noted when lamina propria cells were used as APC. IL-4 was not detected in supernatants from cultures of non-immune T cells in the presence of APC from any tissue. Phenotypic analysis of the cells in cultures of naive T cells, with antigen and APC from different gut-associated tissues revealed important differences. Cells from Peyer's patch, mesenteric lymph node and spleen gave rise to cultures containing largely CD4+CD8- cells. However, cultures in which lamina propria cells acted as APC consisted primarily of CD4-CD8+ cells.     

Antigen-specific and polyclonal CD4+ lamina propria T-cell lines: phenotypic and functional characterization.

Surface phenotype and function of lamina propria CD4+ T cells have been evaluated. In addition, long-term, antigen-specific and polyclonal lamina propria CD4+ T-cell lines have been generated and characterized. Lamina propria CD4+ T cells represent approximately 30% of lamina propria lymphocytes and are responsive to a variety of T-cell mitogens, including anti-CD3, concanavalin A, phytohaemagglutinin and pokeweed mitogen. In each case, however, lamina propria T cells are less responsive to these mitogens than spleen T cells. Freshly isolated lamina propria T cells produce substantial amounts of interleukin-2 (IL-2), interleukin-4 (IL-4), gamma interferon and to a lesser extent interleukin-5 (IL-5). Antigen-specific lamina propria CD4+ T-cell lines were generated by orally immunizing animals with antigen (KLH) in conjunction with cholera toxin as an oral adjuvant. Polyclonal lamina propria CD4+ T-cell lines were generated from unimmunized animals using anti-CD3 as a polyclonal stimulus. Both antigen-specific and polyclonal CD4+ T-cell lines were Thy-1+, alpha beta TCR+ and CD8-. The antigen-specific CD4+ T-cell line when stimulated by anti-CD3 and PMA produces predominantly IL-2, IL-4 and gamma interferon, with very little IL-5. In contrast, the polyclonal CD4+ T-cell line when similarly stimulated produces predominantly IL-4 and IL-5, with very little IL-2 and no detectable gamma interferon. In summary, lamina propria CD4+ T cells have been evaluated and in vitro conditions have been determined for successful generation of lamina propria CD4+ T-cell lines.     

Regulation of cytokine production by human Th0 cells following stimulation with peptide analogues: differential expression of TGF-beta in activation and anergy.

The different biological activities of T-cell-derived cytokines and their level of production influences the qualitative nature of immune responses and, in certain forms of T-cell tolerance, the lack of antigen responsiveness is associated with the production of transforming growth factor-beta (TGF-beta) and interleukin-4 (IL-4). In this study we have investigated the effects of T-cell receptor (TCR) ligation with peptide analogues and the native peptide, in the presence and absence of costimulation, on cytokine production by human T-helper type 0 (Th0) cells reactive with influenza virus haemagglutinin (HA) peptide (HA306-318) and restricted by HLA-DRB1*0101. We observed that resting Th0 cells constitutively produced TGF-beta, but when stimulated with peptide and antigen-presenting cells (APC) under conditions that induce clonal expansion, TGF-beta secretion was abrogated. Furthermore, exposure of the T cells to the wild-type HA peptide under conditions that induce T-cell anergy resulted in the secretion of TGF-beta, and subsequent antigenic rechallenge was unable to override this signal and down-regulate TGF-beta production. Stimulation with altered TCR ligands that failed to induce proliferation also resulted in marked production of TGF-beta, although in many instances the levels were less than those observed in the total absence of antigen, suggesting that partial signalling has occurred. Although in general, there was a direct positive correlation between proliferation and the production of IL-2, IL-4 and interferon-gamma (IFN-gamma) following stimulation with certain analogues, the production of selected cytokines was dissociated.     

IL-27, targeting antigen-presenting cells,promotes Th17 differentiation and colitis in mice

T helper type 17 (Th17) cells have been implicated in autoimmunity and inflammatory bowel disease (IBD). Antigen-presenting cell (APC) -derived cytokines such as interleukin (IL)-1β and IL-6 are key mediators supporting Th17 differentiation, yet how these factors are induced in vivo remains unclear. Here, we show that IL-27 acting on APCs enhances IL-6 and IL-1β production and Th17 differentiation. IL-27Rα−/− T-cell receptor (TCR)β−/− recipients fail to develop gut inflammation following naive CD4 T-cell transfer, whereas IL-27Rα+/+ TCRβ−/− recipients develop severe colitis. Investigation of T-cell responses exhibits that IL-27Rα−/− TCRβ−/− mice do not support Th17 differentiation with significantly decreased levels of IL-6 and IL-1β by APCs. Our study has identified a novel proinflammatory role for IL-27 in vivo that promotes Th17 differentiation by inducing Th17-supporting cytokines in APCs.     

Efficient Presentation of House Dust Mite Allergen Der p 2 by Monocyte-Derived Dendritic Cells and the Role of β2 Integrins

Monocyte-derived dendritic cells (MDDC) are potent antigen-presenting cells (APC). The APC functions of MDDC in allergy were examined. MDDC presentation of the major house dust mite allergen Der p 2 resulted in 4–12-fold higher T-cell proliferation and markedly higher IFN-γ and IL-5 production than PBMC cultures. Comparable T-cell proliferation was obtained with 10-fold fewer MDDC than purified monocytes. MDDC cultured from adherent cells, or CD14⁺, CD11b⁺ or Percoll-purified monocytes were comparable in presenting soluble Ag, and in stimulating allogeneic MLR. Importantly, MDDC presentation of Der p 2 resulted in both Th1 and Th2 stimulation, although MDDC are known to produce high levels of IL-12 and stimulate biased Th1 responses. The basis for the potent APC function of MDDC was further examined. MDDC were found to be highly phagocytic. Immunoprecipitation studies showed markedly elevated ICAM-1 expression but > 10-fold reduction in LFA-1 expression on MDDC compared with monocytes. Monoclonal antibody (MoAb)-blocking experiments showed that ICAM–LFA-1 interaction was essential for MDDC stimulation of Der p 2-specific T-cell proliferative responses. These results show that the use of MDDC as APC provides a simple, sensitive and versatile method for detecting T-cell responses to allergens and that the strong phagocytic capability and the increased ICAM-1 expression of MDDC contribute significantly to their Ag presentation potency.     

Efficient presentation of house dust mite allergen Der p 2 by monocyte-derived dendritic cells and the role of beta 2 integrins

Monocyte-derived dendritic cells (MDDC) are potent antigen-presenting cells (APC). The APC functions of MDDC in allergy were examined. MDDC presentation of the major house dust mite allergen Der p 2 resulted in 4-12-fold higher T-cell proliferation and markedly higher IFN-gamma and IL-5 production than PBMC cultures. Comparable T-cell proliferation was obtained with 10-fold fewer MDDC than purified monocytes. MDDC cultured from adherent cells, or CD14+, CD11b+ or Percoll-purified monocytes were comparable in presenting soluble Ag, and in stimulating allogeneic MLR. Importantly, MDDC presentation of Der p 2 resulted in both Th1 and Th2 stimulation, although MDDC are known to produce high levels of IL-12 and stimulate biased Th1 responses. The basis for the potent APC function of MDDC was further examined. MDDC were found to be highly phagocytic. Immunoprecipitation studies showed markedly elevated ICAM-1 expression but > 10-fold reduction in LFA-1 expression on MDDC compared with monocytes. Monoclonal antibody (MoAb)-blocking experiments showed that ICAM-LFA-1 interaction was essential for MDDC stimulation of Der p 2-specific T-cell proliferative responses. These results show that the use of MDDC as APC provides a simple, sensitive and versatile method for detecting T-cell responses to allergens and that the strong phagocytic capability and the increased ICAM-1 expression of MDDC contribute significantly to their Ag presentation potency.     

The proportion of Th1 cells, which prevail in gut mucosa, is decreased in inflammatory bowel syndrome

T lymphocytes and their cytokines have an important role in the regulation of immune responses in the gut and in the pathogenesis of intestinal inflammation such as in Crohn's disease. The aim of this study was to analyse the Th1/Th2 cytokine profile (IFN-gamma, IL-2, IL-4 and IL-10) in intraepithelial lymphocytes (IEL) and lamina propria lymphocytes (LPL) in Crohn's disease (CD) and ulcerative colitis (UC) in relation to healthy controls (C). Colonic and ileal biopsy specimens were obtained from controls (n = 13) and patients with CD (n = 32). Colonic biopsies were obtained from patients with UC (n = 11). Intracytoplasmic IFN-gamma, IL-2, IL-4 and IL-10 were determined by flow cytometry after PMA-ionomycin stimulation in IEL and LPL. In colonic LPL, a significant proportional decrease of IFN-gamma and IL-2 producing CD3+ cells was observed in patients with CD and UC compared to controls. In ileal LPL, a similar tendency was found although differences were not significant. In IEL no differences in cytokine profiles could be observed. Flow cytometric analysis of intracytoplasmic cytokines at single cell level showed a proportional decrease of IFN-gamma and IL-2 producing T cells in colonic lamina propria in patients with inflammatory bowel disease.     

Localization of IFN-gamma and IL-6 mRNA in murine intestine by in situ hybridization.

Previous studies have highlighted the importance of CD4+ T cells in regulation of IgA responses and have indicated a functional heterogeneity among these cells between inductive (Peyer's patch) and effector (lamina propria) sites in the intestine. To determine whether these functional differences could be accounted for by differences in cytokine profile of cells in each of these sites, the distribution of mRNA for interferon-gamma (IFN-gamma) and interleukin-6 (IL-6) was investigated by in situ hybridization techniques using 35S-labelled riboprobes. Whereas message for IL-6 is abundant in all regions of the lamina propria from the base of the mucosa to the tips of the villi, very little is expressed in Peyer's patches or in the epithelium. In contrast, message for IFN-gamma is expressed predominantly by cells localized only in the base of the lamina propria and, as with IL-6, very little message was detected in Peyer's patches although occasional strongly positive IFN-gamma cells were observed in the epithelium. These results indicate that, at least in the absence of deliberate intestinal stimulation, functional expression of these cytokines is restricted to effector rather than induction sites in the intestine. This is consistent with our previous observations demonstrating a requirement for T-cell signals in promoting post-extravasation differentiation and proliferation of IgA-committed B cells in vivo and the implications of these findings to the role of the Th1 and Th2 subsets of CD4+ cells in mucosal immune responses is discussed.     

Interferon-gamma receptor-deficient mice exhibit impaired gut mucosal immune responses but intact oral tolerance.

Interferon-gamma (IFN-gamma) receptor knock-out (IFN-gamma R -/-) mice were used to analyse the role of IFN-gamma in mucosal immune responses following oral immunization. We found that the IFN-gamma R -/- mice demonstrated 50% reduced spot-forming cell (SFC) responses in the gut lamina propria and spleen after oral immunization with keyhold limpet haemocyanin (KLH) plus cholera toxin (CT) adjuvant. The IFN-gamma R -/- mice exhibited 10-fold reduced total serum KLH-specific antibody levels compared with wild-type mice after oral immunization, while after intravenous immunization, no such difference was seen, suggesting a selective impairment of mucosal immune responses. Moreover, oral immunizations resulted in impaired interleukin-4 (IL-4), IL-10 and IFN-gamma production by spleen T cells from IFN-gamma R -/- mice, indicating that no reciprocal up-regulation of Th2-activities had occurred despite the lack of IFN-gamma R function. No reduction in Th1 or Th2 cytokines was observed following systemic immunizations. Despite potentially strong modulating effects of IFN-gamma on epithelial cell IgA transcytosis and electrolyte barrier functions, CT-immunized IFN-gamma R -/- mice demonstrated unaltered protection against CT in ligated intestinal loops together with normal anti-CT IgA and total IgA levels in gut lavage. Oral feeding with KLH followed by parenteral immunization resulted in strongly suppressed SFC numbers and reduced cell-mediated immunity in both wild-type and IFN-gamma R -/- mice. CT-adjuvant abrogated induction of oral tolerance in both IFN-gamma R -/- and wild-type mice. Collectively, our data argue that the two major response patterns induced by oral administration of protein antigen, i.e. active IgA immunity and oral tolerance, are differently regulated. Thus, IFN-gamma R -/- mice have impaired mucosal immune responses while induction of oral tolerance appears to be unaffected by the lack of IFN-gamma functions.     

Functional expression of 4-1BB (CD137) in the inflammatory tissue in Crohn's disease

4-1BB ligand (L) expressed on antigen presenting cells (APC) interacts with 4-1BB, expressed on activated T cells and this interaction costimulates T cells to secrete cytokines and to proliferate. We investigated whether 4-1BB/4-1BBL interactions might be involved in the pathogenesis of Crohn's disease (CD). In immunohistochemistry, we found 4-1BB expression on lamina propria (LP) cells in inflamed and to a lesser extend in non-inflamed gut tissue from CD patients. mRNA levels for 4-1BB were also elevated in intestinal CD tissue. In contrast, only few 4-1BB-expressing cells were found in inflamed tissue from ulcerative colitis (UC) patients and almost no positive cells were found in control intestinal tissue. 4-1BB expression was better sustained on in vitro activated lamina propria T cells from CD patients compared to controls. Finally, agonistic anti-4-1BB antibody enhanced interferon-gamma (IFN-gamma) production and proliferation of lamina propria T cells from CD patients. Taken together, our data suggest that 4-1BB/4-1BBL interactions contribute to the persistence of gut inflammation in CD.     

Defective Th1 and Th2 cytokine synthesis in the T-T cell presentation model for lack of CD40/CD40 ligand interaction

In this study, T or NK cell clones used as antigen-presenting cells (T- or NK-APC) were shown to be significantly less efficient than professional APC in inducing Th1 and Th2 cytokines by antigen-specific T cell clones. This phenomenon was not related to a limited engagement of TCR by T-APC, since comparable thresholds of TCR down-regulation were shown when antigen was presented by either T-APC or professional APC. Rather, the stimulatory T-APC weakness was due to their inability, because they are CD40⁻, to provide the appropriate co-stimuli to responder T cells both indirectly via IL-12, and partially via direct CD40L triggering on T cells. Indeed, the simultaneous addition of IL-12 and reagents directly engaging CD40L on responder T cells restored T cell cytokine synthesis when antigen was presented by T-APC. In addition, either IL-12 production or blocking of T cell cytokine synthesis by anti-IL-12 p75 antibodies was evident only when professional APC were used in our antigen-specific system. The down-regulation of cytokine synthesis in the system of T-T cell presentation could represent a novel mechanism of immune regulation, which may intervene to switch off detrimental Th1- or Th2-mediated responses induced by antigen presentation among activated T cells infiltrating inflamed tissues.     

Increased intracellular Th1 cytokines in scid mice with inflammatory bowel disease

Severe combined immunodeficient (scid) mice engrafted with small pieces of full thickness gut wall from immunocompetent syngenic donors develop a chronic and lethal colitis. Lymphocytes from the lamina propria of engrafted mice were analyzed for phorbol ester/ionomycin-induced cytokine production by intracellular staining. A 4 – 5-fold increase in the fraction of IFN-γ-producing CD4+ lamina propria T cells was found in moderately and severely diseased mice when compared to healthy congenic C.B-17 control mice. The number of IL-2-producing T cells was increased by approximately 2-fold when comparing mice suffering from severe disease to healthy control mice. The fraction of TNF-α positive CD4+ T cells was increased by a factor of two in both moderately and severely diseased mice. When analyzing Th2 cytokines, it was found that the levels of IL-4-producing CD4+ T cells was not altered in diseased animals, whereas the fraction IL-10-producing CD4+ T cells was reduced by a factor of 20. The combined data showed a 15 – 25-fold increase in the Th1/Th2 ratio of diseased mice when compared to healthy control mice. No intracellular cytokines could be detected in lymphocytes not treated with phorbol ester/ionomycin. The present data identify a prominent role for Th1-type T helper cells in the immunopathogenesis of gut wall graft-induced inflammatory bowel disease in scid mice.     

The central nervous system environment controls effector CD4+ T cell cytokine profile in experimental allergic encephalomyelitis

In experimental allergic encephalomyelitis (EAE), CD4⁺ T cells infiltrate the central nervous system (CNS). We derived CD4⁺ T cell lines from SJL/J mice that were specific for encephalitogenic myelin basic protein (MBP) peptides and produced both Th1 and Th2 cytokines. These lines transferred EAE to naive mice. Peptide-specific cells re-isolated from the CNS only produced Th1 cytokines, whereas T cells in the lymph nodes produced both Th1 and Th2 cytokines. Mononuclear cells isolated from the CNS, the majority of which were microglia, presented antigen to and stimulated MBP-specific T cell lines in vitro. Although CNS antigen-presenting cells (APC) supported increased production of interferon (IFN)-γ mRNA by these T cells, there was no increase in the interleukin (IL)-4 signal, whereas splenic APC induced increases in both IFN-γ and IL-4. mRNA for IL-12 (p40 subunit) was up-regulated in both infiltrating macrophages and resident microglia from mice with EAE. We have thus shown that a Th1 cytokine bias within the CNS can be induced by CNS APC, and that IL-12 is up-regulated in microglial cells within the CNS of mice with EAE. Microglia may therefore control Th1 cytokine responses within the CNS.     

Alternative versus classical activation of macrophages.

In parallel to the Th1/Th2 paradigm, antigen-presenting cells (APC) are divided into classically activated APC (dendritic cells/effector macrophages) and alternatively activated APC (IL-4-induced, alternatively activated macrophages/IL-10-induced, immature dendritic cells). Alternatively activated APC share a special molecular repertoire including receptors of innate immunity with broad specificity for foreign antigen and anti-inflammatory cytokines such as IL-1Ra and alternative macrophage activation-associated CC-chemokine-1. Alternatively activated APC mediated tolerance and downregulated inflammation. Abuse of alternatively activated APC in support of infectious susceptibility or tumor immune escape is counteracted by the classical pathway. Thus, classically and alternatively activated APC secure the balance between proinflammatory and anti-inflammatory immune reactions.     

In Situ Expression of Interleukin-10 in Noninflamed Human Gut and in Inflammatory Bowel Disease

A dysregulated secretion of contra-inflammatory cytokines such as interleukin-10 (IL-10) could play a role in the pathogenesis of inflammatory bowel disease (IBD). We have investigated the expression of IL-10 in gut tissues from patients with Crohn’s disease (CD), ulcerative colitis (UC) and controls by mRNA in situ hybridization and immunohistochemistry. Intestinal epithelial cells were found to express IL-10 mRNA and IL-10 protein in all of the tissues investigated without any major differences in the expression patterns. However, compared with noninflamed gut, significantly increased numbers of mononuclear cells (MNCs) producing IL-10 were present in inflamed gut, both in CD and UC. This cytokine was expressed most prominently by inflammatory infiltrates enriched in macrophages, although T cells seem to contribute to its production as well. Elevated IL-10 expression in IBD was mainly detected in the submucosa, whereas IL-10 production by lamina propria cells remained comparably low. In contrast, the expression of IL-1β mRNA was preferentially increased in the lamina propria. Our data argue against a general deficiency in IL-10 production in IBD. The results suggest rather that the local production of IL-10 by mucosal MNCs in IBD is insufficient to down-regulate pro-inflammatory cytokines such as IL-1β in the lamina propria compartment.     

Type 1 T-helper cell predominance and interleukin-12 expression in the gut of patients with Crohn's disease.

Crohn's disease (CD) is a chronic bowel inflammatory disorder in which the pathogenic role of immune alterations has been suggested, but the immunologic mechanisms responsible for the inflammatory reaction are still poorly understood. We investigated the profile of cytokine secretion by T-cell clones generated from gut tissue specimens of four patients with active CD, five patients with ulcerative colitis, and four patients with noninflammatory gut disorders (NIGDs). The great majority of CD4+ T-cell clones generated from the gut of patients with CD produced high levels of interferon-gamma (IFN-gamma) but low or undetectable amounts of interleukin-4 (IL-4), whereas substantial proportions of CD4+ T-cell clones derived from the gut of patients with either ulcerative colitis or NIGDs produced IL-4 in addition to IFN-gamma. The immunohistochemical analysis revealed high numbers of activated CD4+ T cells showing IFN-gamma but not IL-4 reactivity, as well as substantial proportions of IL-12-containing macrophages, in the intestinal lamina propria and muscularis propria of patients with CD, whereas these cells were very rare or undetectable in patients with NIGDs. Culturing T cells from gut biopsy specimens of a patient with CD in the presence of a neutralizing anti-IL-12 antibody down-regulated the development of IFN-gamma-producing CD4+ T cells. These findings suggest that a critical event in the initiation of bowel inflammatory lesions in CD may involve up-regulation of IL-12 production, resulting in conditions that maximally promote type 1 T-helper immune responses.     

Costimulatory molecules in the developing human gastrointestinal tract: a pathway for fetal allergen priming

BACKGROUND: Antigen-specific responses can be detected in umbilical cord blood mononuclear cells. The fetal immune system must therefore attain a level of maturity compatible with the initiation of such responses as well as be exposed to antigen. OBJECTIVE: We sought to assess the expression of costimulatory molecules in fetal gut and the presence of cytokines in amniotic fluid at this time as a preliminary analysis of the suitability of the fetal gut as a site of antigen priming during intrauterine life. METHODS: Human fetal gut was analyzed for cells expressing costimulatory molecules through use of immunohistochemistry. Amniotic fluid was studied by ELISA, for cytokines regulating the nature of the response, and as a source of the common dietary antigen ovalbumin. RESULTS: MHC class II--positive cells were abundant over the period examined (11-24 weeks of gestation), other surface antigens showing spatial and temporal variation in expression. From 11 to 14 weeks of gestation, CD68-positive and CD40-positive cells, like MHC class II--positive cells, were present throughout the lamina propria; few CD3-positive cells (T cells) were observed. With the emergence of lymphoid aggregates (14-16 weeks), CD83-positive cells (dendritic cells) and CD20-positive cells (B cells) could be detected in fetal gut; however, expression was restricted to the lymphoid aggregates. In contrast, MHC class II, CD40, and CD68 continued to be expressed in the lamina propria. CD28-positive cells were also evident from 14 weeks of gestation, occurring throughout the lamina propria and lymphoid aggregates; this corresponded to the increasing numbers of CD3-positive cells. The occasional CD86-positive, CD40L-positive, or CTLA4-positive cell could be seen in or around lymphoid aggregates after 14 weeks of gestation. Lymphoid follicles forming after 16 weeks of gestation contained MHC class II--positive, CD83-positive, CD20-positive, CD40-positive, CD86-positive, CD3-positive, CD28-positive, CD40L-positive, and CTLA4-positive cells. MHC class II--positive, CD40-positive, CD68-positive, CD3-positive, and CD28-positive cells continued to be present in the lamina propria at this time. At all times studied, CD14 was not expressed in the lamina propria or lymphoid follicles. Prostaglandin E(2), TGF beta(1), and IL-10 dominated the amniotic fluid cytokine milieu, and ovalbumin was also detectable in amniotic fluid from 3 of 26 women who had detectable circulating levels. CONCLUSION: Of the costimulatory molecules studied, CD40 was the most abundant. However, both of the ligand families studied (CD40-CD40L and CD86-CD28/CD152) could provide the costimulatory signals required for the initiation of antigenspecific reactivity in the gastrointestinal tract of the human fetus as early as 16 weeks of gestation. The cytokine milieu would favor the development of T(H)2-type reactivity to antigens, such as ovalbumin, that are present at this time.     

Oral macrophage-like cells play a key role in tolerance induction following sublingual immunotherapy of asthmatic mice

Sublingual allergen-specific immunotherapy (SLIT) is a safe and efficacious treatment for type 1 respiratory allergies. Herein, we investigated the key subset(s) of antigen-presenting cells (APCs) involved in antigen/allergen capture and tolerance induction during SLIT. Following sublingual administration, fluorochrome-labeled ovalbumin (OVA) is predominantly captured by oral CD11b⁺CD11c⁻ cells that migrate to cervical lymph nodes (CLNs) and present the antigen to naive CD4⁺ T cells. Conditional depletion with diphtheria toxin of CD11b⁺, but not CD11c⁺ cells, in oral tissues impairs CD4⁺ T-cell priming in CLNs. In mice with established asthma to OVA, specific targeting of the antigen to oral CD11b⁺ cells using the adenylate cyclase vector system reduces airway hyperresponsiveness (AHR), eosinophil recruitment in bronchoalveolar lavages (BALs), and specific Th2 responses in CLNs and lungs. Oral CD11b⁺CD11c⁻ cells resemble tolerogenic macrophages found in the lamina propria (LP) of the small intestine in that they express the mannose receptor CD206, as well as class-2 retinaldehyde dehydrogenase (RALDH2), and they support the differentiation of interferon-γ/interleukin-10 (IFNγ/IL-10)-producing Foxp3⁺ CD4⁺ regulatory T cells. Thus, among the various APC subsets present in oral tissues of mice, macrophage-like cells play a key role in tolerance induction following SLIT.     

Availability of antigen-presenting cells can determine the extent of CD4 effector expansion and priming for secretion of Th2 cytokines in vivo

Like dendritic cells (DC), activated B cells are effective antigen-presenting cells (APC) for na?ve CD4 cells due to their expression of MHC class II and multiple costimulatory molecules. We showed previously that CD4 cells primed in B cell-deficient micro MT) mice undergo more limited expansion than in normal animals after immunization with keyhole limpet hemocyanin. Here we report that in the absence of B cells, priming of effectors with the capacity to produce the Th2 cytokines, IL-4, IL-5 and IL-13, was profoundly reduced whereas the development of effectors that secrete the Th1 cytokine IFN-gamma was much less affected. A blockade of IL-12 reduced priming of IFN-gamma-secreting effectors but did not reverse the IL-4, IL-5, or IL-13 deficiency of the response. CD4 cell expansion and priming for Th2 cytokines in micro MT mice was reconstituted by adoptive transfer of activated splenic B cells, which were present throughout the primary response. However, transfer of splenic DC from either control or micro MT mice also supported development of Th2 cytokine responses, indicating that an APC deficit rather than a unique contribution of B cells accounted for diminished effector priming. We conclude that CD4 cell expansion must be sustained via APC for the development of Th2 cytokine-secreting effectors in vivo and that in responses to protein antigen, B cells can be a crucial population to serve in this role. The results suggest that the level of APC engagement can not only determine the extent of effector expansion, but also the overall Th1/Th2 cytokine balance.     

Susceptibility and Resistance to Leishmania amazonensis in H-2q Syngeneic High and Low Antibody Responder Mice (Biozzi Mice)

H-2 syngeneic H and L (Biozzi) mice provide a model to study Leishmania infections in which polar resistant and susceptible phenotypes are independent from H-2 differences. High-Ab-responder (H) and low-Ab-responder (L) mice syngeneic at the H-2 locus (H-2^q) were, respectively, susceptible and highly resistant to Leishmania amazonensis infection. L-mice resistance was associated with high IFN-γ and transient IL-4 production by lymph node (LN) cells, in contrast with sustained IL-4 and decreasing IFN-γ production by susceptible H mice. IL-12 production could be detected only in LN from resistant mice. The cytokine production pattern was consistent with preferential progression to a Th1-type response in resistant L-mice, and to a Th2-type response in susceptible H-mice. We also investigated whether this shift towards Th1- or Th2-type cytokine responses was dependent upon H or L antigen presenting cells' (APC) intrinsic ability to preferentially stimulate either T-cell subset. To this end, LN-derived T-cell lines were grown from 12-day infected mice, when both strains produced IFN-γ and IL-4. L-derived T-cell lines developed a Th2 cytokine pattern whereas H-derived T-cell lines produced IFN-γ, IL-4 and IL-10 whatever the APC origin (H or L) used for their derivation. This work constitutes the first characterization of cellular immune responses to the intracellular parasite, L. amazonensis in H-2 syngeneic mice, an infection model in which polar resistant and susceptible phenotypes are determined by non-MHC genes.