Suppressive effect of environmental tobacco smoke on murine Th2 cell-mediated nasal eosinophilic inflammation.

BACKGROUND: Environmental tobacco smoke (ETS) exposure is recognized as a risk factor for the development of various respiratory diseases. OBJECTIVE: In this study, the effect of ETS on allergen-immunized and allergen-specific Th2 cell-transferred murine eosinophilic inflammation models and that of cigarette smoke extract (CSE) and nicotine on allergen-induced Th2 cell proliferation and interleukin (IL)-4 production were investigated. METHODS: Ovalbumin (OVA)-immunized and OVA-specific Th2 cell-transferred BALB/c mice were exposed to ETS and were challenged with OVA. Then, the number of inflammatory cells in the nasal mucosa and nasal hyperresponsiveness (NHR) were assessed. The effects of CSE and nicotine on the allergen-induced proliferative response of and IL-4 production by Th2 cells were determined in vitro. RESULTS: In OVA-immunized and Th2 cell-transferred mice, allergen-induced NHR and nasal eosinophil infiltration were significantly suppressed by ETS exposure, whereas the accumulation of neutrophils was rather enhanced. Allergen-specific Th2 cell proliferation and IL-4 production were inhibited by coculture with CSE. The same effects were induced by nicotine, though the effect on proliferation was relatively weak. CONCLUSION: Regardless of its harmful effect, ETS suppresses NHR, probably through the inhibition of Th2 cell responses.

Contribution of neuraminidase 3 to the differentiation of induced regulatory T cells.

Neuraminidase family enzymes that hydrolyze the terminal sialic acid linkage in biomolecules are involved in various immune responses. We previously showed that Th1 and Th2 cells differentially express several neuraminidases. Herein, the expression of neuraminidases in induced regulatory T (iTreg) cells was investigated in comparison with that in other T-cell subsets. Contrary to the tendency toward higher neuraminidase 1 mRNA expression in in vitro-differentiated Th2 cells, compared to Th1, Th17 and iTreg cells, we observed significantly higher expression of neuraminidase 3 (Neu3) in iTreg cells. Furthermore, the expression of Neu3 in FoxP3+ CD62L- spleen cells was higher than that in FoxP3+ CD62L+ and FoxP3- cells. Lentiviral expression of Neu3 in naïve CD4+ T cells during the stimulation culture led to upregulation of FoxP3 expression. On the basis of these findings, we conclude that Neu3 contributes to the differentiation of iTreg cells by upregulation of FoxP3.

Janus Kinase Inhibitor Tofacitinib Shows Potent Efficacy in a Mouse Model of Autoimmune Lymphoproliferative Syndrome (ALPS).

PURPOSE: Autoimmune lymphoproliferative syndrome (ALPS) is a non-malignant genetic disorder of lymphocyte homeostasis with defective Fas-mediated apoptosis. Current therapies for ALPS primarily target autoimmune manifestations with non-specific immune suppressants with variable success thus highlighting the need for better therapeutics for this disorder. METHODS: The spectrum of clinical manifestations of ALPS is mirrored by MRL/lpr mice that carry a loss of function mutation in the Fas gene and have proven to be a valuable model in predicting the efficacy of several therapeutics that are front-line modalities for the treatment of ALPS. We evaluated the potential efficacy of tofacitinib, an orally active, pan-JAK inhibitor currently approved for rheumatoid arthritis as a single agent modality against ALPS using MRL/lpr mice. RESULTS: We demonstrate that a 42-day course of tofacitinib therapy leads to a lasting reversal of lymphadenopathy and autoimmune manifestations in the treated MRL/lpr mice, Specifically, in treated mice the peripheral blood white blood cell counts were reversed to near normal levels with almost a 50 % reduction in the TCRαß(+)CD4(-)CD8(-)T lymphocyte numbers that coincided with a parallel increase in CD8(+) T cells without a demonstrable effect on CD4(+) lymphocytes including FoxP3(+) regulatory T cells. The elevated plasma IgG and IgA levels were also drastically lowered along with a significant reduction in plasmablasts and plasmacytes in the spleen. CONCLUSION: On the basis of these results, it is likely that tofacitinib would prove to be a potent single agent therapeutic modality capable of ameliorating both offending lymphadenopathy as well as autoimmunity in ALPS patients.

Tumor-secreted miR-214 induces regulatory T cells: a major link between immune evasion and tumor growth.

An increased population of CD4(+)CD25(high)Foxp3(+) regulatory T cells (Tregs) in the tumor-associated microenvironment plays an important role in cancer immune evasion. However, the underlying mechanism remains unclear. Here we observed an increased secretion of miR-214 in various types of human cancers and mouse tumor models. Tumor-secreted miR-214 was sufficiently delivered into recipient T cells by microvesicles (MVs). In targeted mouse peripheral CD4(+) T cells, tumor-derived miR-214 efficiently downregulated phosphatase and tensin homolog (PTEN) and promoted Treg expansion. The miR-214-induced Tregs secreted higher levels of IL-10 and promoted tumor growth in nude mice. Furthermore, in vivo studies indicated that Treg expansion mediated by cancer cell-secreted miR-214 resulted in enhanced immune suppression and tumor implantation/growth in mice. The MV delivery of anti-miR-214 antisense oligonucleotides (ASOs) into mice implanted with tumors blocked Treg expansion and tumor growth. Our study reveals a novel mechanism through which cancer cell actively manipulates immune response via promoting Treg expansion.

IL-17A induces hypo-contraction of intestinal smooth muscle via induction of iNOS in muscularis macrophages.

Intestinal inflammation causes disorder in bowel motility. Th17 cytokines are involved in intestinal inflammation. To understand the role of interleukin (IL)-17 in intestinal motility, we examined effects of IL-17A on contractile activities of organ-cultured ileum. Rat ileal smooth muscle strips were organ cultured with IL-17A. Muscle contraction was measured, and cells expressing inducible nitric oxide synthase (iNOS) were identified with immunohistochemistry. Creating Th17-transferred colitis model mice, in vivo effects of IL-17 on contractile activities, and iNOS mRNA expression in colonic smooth muscle were investigated. Treatment with IL-17A for 12 h and 3 days attenuated carbachol- and membrane depolarization-induced contractions in organ-cultured rat ileum. N(G)-Nitro-l-arginine methyl ester (100 µM), a nitric oxide synthase inhibitor, completely reversed the IL-17A-induced inhibition of contractile force. Ileal tissue cultured in the presence of IL-17A showed increased expression of iNOS mRNA and protein. Immunohistochemical analysis using an iNOS antibody revealed that iNOS protein was expressed on ED2-positive muscularis macrophages. The level of iNOS mRNA was also increased in inflamed colonic smooth muscle of Th17-transferred colitis model mice. In intestinal inflammation, IL-17A induces an intestinal motility disorder through iNOS expression in muscularis macrophages.

Tofacitinib, a janus kinase inhibitor demonstrates efficacy in an IL-15 transgenic mouse model that recapitulates pathologic manifestations of celiac disease.

Celiac disease (CD) is an immune-mediated, inflammatory disorder of the small intestines with a defined genetic etiological component associated with the expression of HLA-DQ2 and/or HLA-DQ8 haplotypes. The dietary consumption of gluten-rich cereals triggers a gluten-specific immune response in genetically susceptible individuals leading to a spectrum of clinical manifestations ranging from an inapparent subclinical disease, to overt enteropathy that can in some individuals progress to enteropathy-associated T cell lymphoma (EATL). The tissue-destructive pathologic process of CD is driven by activated NK-like intraepithelial CD8(+) lymphocytes and the proinflammatory cytokine IL-15 has emerged to be pivotal in orchestrating this perpetual tissue destruction and inflammation. Moreover, transgenic mice that over-express human IL-15 from an enterocyte-specific promoter (T3(b)-hIL-15 Tg) recapitulate many of the disease-defining T and B cell-mediated pathologic features of CD, further supporting the evolving consensus that IL-15 represents a valuable target in devising therapeutic interventions against the form of the disease that is especially refractory to gluten-free diet. In the present study, we evaluated the potential efficacy of tofacitinib, a pan-JAK inhibitor that abrogates IL-15 signaling, as a therapeutic modality against CD using T3(b)-hIL-15 Tg mice. We demonstrate that tofacitinib therapy leads to a lasting reversal of pathologic manifestations in the treated mice, thereby highlighting the potential value of tofacitininb as a therapeutic modality against refractory CD for which no effective therapy exists currently. Additionally, the visceral adiposity observed in the tofacitinib-treated mice underscores the importance of continued evaluation of the drug's impact on the lipid metabolism.

Inhibition of allergen-induced airway inflammation by low-dose oral immunotherapy with transgenic rice seeds independently of immunoglobulin e synthesis.

BACKGROUND: Oral immunotherapy is potentially useful for the treatment of allergic diseases. We previously demonstrated that allergen-induced airway inflammation and immunoglobulin E (IgE) production in mice were suppressed by oral administration of high-dose transgenic (Tg) rice seeds (approximately 50 g/kg/day) expressing a T cell epitope of Dermatophagoides pteronyssinus group 1 allergen (Der p 1). However, this amount of Tg rice seeds was not realistic in our daily life. In this study, allergen-induced airway inflammation and IgE production following oral immunotherapy with a realistic (lowest) dose of Tg rice seeds were investigated. METHODS: Mice orally administered with Tg or non-Tg rice seeds at approximately 5 g/kg/day for 1 week were immunized with recombinant Der p 1, and then challenged with the corresponding allergen. The infiltration of inflammatory cells into the airways and the levels of allergen-specific serum IgE were examined. RESULTS: Low-dose oral administration of Tg rice seeds significantly inhibited the allergen-induced infiltration of eosinophils and lymphocytes into the airways, but allergen-specific IgE synthesis was not changed. CONCLUSIONS: Low-dose oral immunotherapy with Tg rice seeds could suppress allergen-induced airway inflammation through mechanisms other than the downregulation of IgE synthesis.

Prevention of allergic asthma by vaccination with transgenic rice seed expressing mite allergen: induction of allergen-specific oral tolerance without bystander suppression.

This study tested the feasibility of oral immunotherapy for bronchial asthma using a newly developed subunit vaccine in which a fragment (p45-145) of mite allergen (Der p 1) containing immunodominant human and mouse T cell epitopes was encapsulated in endoplasmic reticulum-derived protein bodies of transgenic (Tg) rice seed. Allergen-specific serum immunoglobulin responses, T cell proliferation, Th1/Th2 cytokine production, airway inflammatory cell infiltration, bronchial hyper-responsiveness (BHR) and lung histology were investigated in allergen-immunized and -challenged mice. Prophylactic oral vaccination with the Tg rice seeds clearly reduced the serum levels of allergen-specific IgE and IgG. Allergen-induced CD4(+) T cell proliferation and production of Th2 cytokines in vitro, infiltration of eosinophils, neutrophils and mononuclear cells into the airways and BHR were also inhibited by oral vaccination. The effects of the vaccine were antigen-specific immune response because the levels of specific IgE and IgG in mice immunized with Der f 2 or ovalbumin were not significantly suppressed by oral vaccination with the Der p 1 expressing Tg rice. Thus, the vaccine does not induce nonspecific bystander suppression, which has been a problem with many oral tolerance regimens. These results suggest that our novel vaccine strategy is a promising approach for allergen-specific oral immunotherapy against allergic diseases including bronchial asthma.

Rice seed ER-derived protein body as an efficient delivery vehicle for oral tolerogenic peptides.

Mucosal delivery of peptide/protein therapeutics via the oral route is a desirable strategy in human immunotherapy. A key step for enhancing the bioavailability of orally administered therapeutics is to protect them from enzymatic digestion in the gastrointestinal tract. Here, we generated transgenic rice seeds accumulating allergen-derived T cell epitopes, a model tolerogen for the control of pollen allergy, in either ER-derived protein body-I (PB-I) or protein storage vacuole protein body-II (PB-II). Compared with PB-II-localized or chemically synthesized forms, PB-I-localized T cell epitopes showed higher resistance to enzymatic digestion in simulated gastric fluid. Moreover, the dose of T cell epitope required for suppression of allergen-specific IgE in mice was about 20-fold lower when fed in PB-I localized form than when unprotected. These findings demonstrate the potential of bioencapsulation in PB-I for broad applications as a viable strategy to achieve efficient mucosal delivery of oral peptide/protein therapeutics.

The use of a mutant TNF-alpha as a vaccine adjuvant for the induction of mucosal immune responses.

Safe and potent adjuvants are required in order to establish effective mucosal vaccines. Cytokines are promising adjuvants because they are human-derived safe biomaterial and display immune-modulating functions. We have created a mutant tumor necrosis factor-alpha (TNF-alpha), mTNF-K90R, that exhibits high bioactivity and resistance to proteases. Here, we examined the potential of mTNF-K90R as a mucosal adjuvant. Initially, we showed that intranasal co-administration of mTNF-K90R with ovalbumin (OVA) potently produced OVA-specific Immunoglobulin (Ig) G antibodies (Abs) in serum and IgA Abs both at local and distal mucosal sites compared to co-administration with wild-type TNF-alpha. The OVA-specific immune response was characterized by high levels of serum IgG1 and increased production of interleukin-4 (IL-4), IL-5 and IL-10 from splenocytes of immunized mice, suggesting a Th2 response. Furthermore, intranasal immunization with an antigen from influenza virus plus mTNF-K90R exhibited mucosal adjuvant activity for induction of both systemic and mucosal immune responses. Importantly, histopathological examination of the nasal tissue of mTNF-K90R treated mice detected no signs of toxicity. These findings suggest that mTNF-K90R is safe and effective mucosal adjuvant and this system may have potential application as a universal mucosal adjuvant system for mucosal vaccines improving the immune response to a variety of viral antigens.

Development of transgenic rice expressing mite antigen for a new concept of immunotherapy.

BACKGROUND: To elucidate the usefulness of antigen-specific immunotherapy based on oral vaccination with an edible part of the plant, we examined the effect of transgenic (Tg) rice seeds expressing an immunodominant fragment of the group 1 antigen of Dermatophagoides pteronyssinus (Der p 1) on a murine model of asthma. METHODS: Mice were orally vaccinated with the Tg or non-Tg rice seeds for 2 weeks, then they were immunized with recombinant Der p 1 (rDer p 1) and alum intraperitoneally. Antigen-induced immune responses, such as proliferation and cytokine production of CD4+ T cells, antigen-specific serum IgE and IgG, and infiltration of inflammatory cells into the airways were investigated in those mice. RESULTS: The proliferation and Th2 cytokine production of CD4+ T cells in vitro, antigen-specific IgE and IgG synthesis as well as accumulation of eosinophils and lymphocytes into the airways in vivo were significantly inhibited by administration of the Tg rice. CONCLUSIONS: These results suggest that the edible vaccines using Tg rice seeds are useful for the treatment of allergic disorders including bronchial asthma.

TNF superfamily member, TL1A, is a potential mucosal vaccine adjuvant.

The identification of cytokine adjuvants capable of inducing an efficient mucosal immune response against viral pathogens has been long anticipated. Here, we attempted to identify the potential of tumor necrosis factor superfamily (TNFS) cytokines to function as mucosal vaccine adjuvants. Sixteen different TNFS cytokines were used to screen mucosal vaccine adjuvants, after which their immune responses were compared. Among the TNFS cytokines, intranasal immunization with OVA plus APRIL, TL1A, and TNF-alpha exhibited stronger immune response than those immunized with OVA alone. TL1A induced the strongest immune response and augmented OVA-specific IgG and IgA responses in serum and mucosal compartments, respectively. The OVA-specific immune response of TL1A was characterized by high levels of serum IgG1 and increased production of IL-4 and IL-5 from splenocytes of immunized mice, suggesting that TL1A might induce Th2-type responses. These findings indicate that TL1A has the most potential as a mucosal adjuvant among the TNFS cytokines.

Differential contribution of NFATc2 and NFATc1 to TNF-alpha gene expression in T cells.

The NFAT family transcription factors play crucial roles in immunological and other biological events; however, the functional differences among NFAT members have not been fully elucidated. This study investigated the relative contribution of NFATc2 and NFATc1 to the transactivation of cytokine genes in T cells. Ectopic expression of NFATc2 but not NFATc1, especially its short isoform, enhanced TNF-alpha synthesis in human T cells at the gene transcription level, whereas both NFATs augmented IL-2 expression. In addition, a reduction of the shortest NFATc1 isoform using RNA interference technology failed to suppress TNF-alpha expression. The promoter/enhancer activity of the NFAT-binding site in the TNF-alpha gene was up-regulated by NFATc2 but not by NFATc1, whereas both NFATs associated similarly with this region. A study of mRNA expression using NFATc2/NFATc1 chimeric molecules revealed that the enhancing activity of NFAT on the TNF-alpha gene was lost by truncation of its C-terminal transactivation domain. In addition, this domain derived from NFATc2 behaved as a dominant negative against the NFAT site in TNF-alpha promoter-dependent transcriptional activity in T cells. We conclude that the C-terminal transactivation domain in NFAT is crucial for TNF-alpha gene expression in human T cells.

Therapeutic effects of roxithromycin in interleukin-10-deficient colitis.

BACKGROUND: A limited number of therapeutic strategies are currently available to treat patients with inflammatory bowel disease (IBD). Interleukin-10 (IL-10)-deficient mice, well characterized as an experimental model of IBD, develop severe chronic colitis because of aberrant Th1 responses. Roxithromycin (RXM), a macrolide antibiotic, has received attention because it offers not only antibacterial but also immunosuppressive effects. We examined the immunosuppressive effect of RXM on the development of IBD. METHODS: To test the efficacy of short-term administration of RXM, elder IL-10-deficient mice (16-20 weeks old) with established colitis were orally treated for 10 days with RXM (20 mg/kg per day). To test the long-term preventive effects of RXM, for 20 weeks young adult IL-10-deficient mice (4-5 weeks old) also were administered RXM orally (20 mg/kg per day). RESULTS: The short-term treatment-oriented administration of RXM reduced the degree of inflammatory change and lowered serum amyloid A in IL-10-deficient mice with severe colitis. Mononuclear cells from the lamina propria of RXM-treated large intestines showed lower production of IFN-gamma than did those from diseased mice that were untreated. Long-term prevention-oriented administration of RXM suppressed the development of severe colitis and decreased production of IFN-gamma and IL-12. In addition to its expected immunosuppressive effect, RXM treatment also decreased the level of Bacteroides vulgatus, a Gram-negative anaerobe. CONCLUSIONS: The anti-inflammatory changes observed in IL-10-deficient mice resulted from the efficacy of RXM as an immunosuppressant as well as from its efficacy as an antibiotic. According to our findings, RXM would seem to have significant potential as a preventive and/or therapeutic agent for IBD.

Peptide immunotherapy for allergic diseases using a rice-based edible vaccine.

PURPOSE OF REVIEW: Plant pollens are the most common cause of seasonal allergic disease. The number of patients undergoing treatment for allergies to the pollen of Japanese cedar (major antigens: Cry j 1 and Cry j 2) has increased steadily each year. Integration of an effective, safe and inexpensive clinical program would be greatly improved by addressing deficiencies in systemically delivered immunotherapy. RECENT FINDINGS: We have demonstrated that feeding mice transgenic rice seeds accumulating the T-cell epitope peptides of Cry j 1 and Cry j 2 before systemic challenge with total protein of cedar pollen inhibits the development of allergen-specific IgE, IgG and CD4 T-cell proliferative responses. The levels of allergen-specific CD4 T-cell-derived allergy-associated T-helper 2 cytokine of IL-4, IL-5, and IL-13 and histamine release in serum were also significantly decreased. Moreover, clinical symptoms were inhibited in an experimental sneezing-mouse model. SUMMARY: Plant-based edible vaccine has been shown to be effective for treatment of Japanese cedar pollinosis. When rice seeds containing T-cell epitopes derived from cedar pollen allergens were orally administered to mice, immune tolerance leading to reduction of allergen-specific IgE, T-cell proliferative reaction and histamine could be induced, resulting in suppression of allergic-specific symptoms such as sneezing.

CCR7 is critically important for migration of dendritic cells in intestinal lamina propria to mesenteric lymph nodes.

Although dendritic cells (DCs) located in the small intestinal lamina propria (LP-DCs) migrate to mesenteric lymph nodes (MLNs) constitutively, it is unclear which chemokines regulate their trafficking to MLNs. In this study we report that LP-DCs in unperturbed mice require CCR7 to migrate to MLNs. In vitro, LP-DCs expressing CCR7 migrated toward CCL21, although the LP-DCs appeared morphologically and phenotypically immature. In MLNs, DCs bearing the unique LP-DC phenotype (CD11chighCD8alphaintCD11blowalphaLlowbeta7high and CD11chighCD8alpha-CD11bhighalphaLlowbeta7high) were abundant in wild-type mice, but were markedly fewer in CCL19-, CCL21-Ser-deficient plt/plt mice and were almost absent in CCR7-deficient mice, indicating the critical importance of CCR7 in LP-DC trafficking to MLNs. Interestingly, CCR7+ DCs in MLNs with the unique LP-DC phenotype had numerous vacuoles containing cellular debris in the cytoplasm, although MLN-DCs themselves were poorly phagocytic, suggesting that the debris was derived from the LP, where the LP-DCs ingested apoptotic intestinal epithelial cells (IECs). Consistent with this, LP-DCs ingested IECs vigorously in vitro. By presenting IEC-associated Ag, the LP-DCs also induce T cells to produce IL-4 and IL-10. Collectively, these results strongly suggest that LP-DCs with unique immunomodulatory activities migrate to MLNs in a CCR7-dependent manner to engage in the presentation of IEC-associated Ags acquired in the LP.

Colitis in mice lacking the common cytokine receptor gamma chain is mediated by IL-6-producing CD4+ T cells.

BACKGROUND & AIMS: Mice that have a truncated mutation of the common cytokine receptor gamma chain (CR gamma -/Y) are known to spontaneously develop colitis. To identify the pathologic elements responsible for triggering this localized inflammatory disease, we elucidated and characterized aberrant T cells and their enteropathogenic cytokines in CR gamma -/Y mice with colitis. METHODS: The histologic appearance, cell population, T-cell receptor V beta usage, and cytokine production of lamina propria lymphocytes were assessed. CR gamma -/Y mice were treated with anti-interleukin (IL)-6 receptor monoclonal antibody to evaluate its ability to control colitis, and splenic CD4 + T cells from the same mouse model were adoptively transferred into SCID mice to see if they spurred the appearance of colitis. RESULTS: We found marked thickening of the large intestine, an increase in crypt depth, and infiltration of the colonic lamina propria and submucosa with mononuclear cells in the euthymic CR gamma -/Y mice, but not in the athymic CR gamma -/Y mice, starting at the age of 8 weeks. Colonic CD4 + T cells with high expressions of antiapoptotic Bcl-x and Bcl-2 were found to use selected subsets (V beta 14) of T-cell receptor and to exclusively produce IL-6. Treatment of CR gamma -/Y mice with anti-IL-6 receptor monoclonal antibody prevented the formation of colitis via the induction of apoptosis in IL-6-producing CD4 + T cells. Adoptive transfer of pathologic CD4 + T cells induced colitis in the recipient SCID mice. CONCLUSIONS: Colonic IL-6-producing thymus-derived CD4 + T cells are responsible for the development of colitis in CR gamma -/Y mice.

Prenatal blockage of lymphotoxin beta receptor and TNF receptor p55 signaling cascade resulted in the acceleration of tissue genesis for isolated lymphoid follicles in the large intestine.

Signaling by lymphotoxin (LT) and TNF is essential for the organogenesis of secondary lymphoid tissues in systemic and mucosal compartments. In this study, we demonstrated that the progeny of mice treated with fusion protein of LTbetaR and IgGFc (LTbetaR-Ig) or LTbetaR-Ig plus TNFR55-Ig (double Ig) showed significantly increased numbers of isolated lymphoid follicles (ILF) in the large intestine. Interestingly, double Ig treatment accelerated the maturation of large intestinal ILF. Three-week-old progeny of double Ig-treated mice showed increased numbers of ILF in the large intestine, but not in the small intestine. Furthermore, alteration of intestinal microflora by feeding of antibiotic water did not affect the increased numbers of ILF in the large intestine of double Ig-treated mice. Most interestingly, mice that developed numerous ILF also had increased levels of activation-induced cytidine deaminase expression and numbers of IgA-expressing cells in the lamina propria of the large intestine. Taken together, these results suggest that ILF formation in the large intestine is accelerated by blockage of LTbetaR and TNFR55 signals in utero, and ILF, like colonic patches, might play a role in the induction of IgA response in the large intestine.

Role of gut-associated lymphoreticular tissues in antigen-specific intestinal IgA immunity.

This study assessed the roles of the postnatal lymphotoxin-beta receptor (LTbetaR)-mediated signals in the gut-associated lymphoreticular tissues of mice for subsequent regulation of Ag-specific intestinal IgA responses. Blockade of LTbetaR-dependent events by postnatal administration of the fusion protein of LTbetaR and IgG Fc (LTbetaR-Ig) reduced both the size and numbers of Peyer's patches (PP) without influencing the PP microarchitecture. Interestingly, inhibition of LTbetaR-dependent signaling revealed significant reductions in the formation of follicular dendritic cell clusters in mesenteric lymph nodes (MLN). Furthermore, these postnatal signaling events controlled the development of isolated lymphoid follicles (ILF) because treatment with LTbetaR-Ig eliminated the formation of ILF. LTbetaR-Ig-treated mice with altered microarchitecture of MLN and lacking ILF were still able to produce significant Ag-specific mucosal IgA responses after oral immunization; however, the levels were significantly lower than those seen in control mice. These results imply the importance of ILF for Ag-specific intestinal immunity. However, mice treated with both TNFR55-Ig and LTbetaR-Ig in utero, which lack PP and MLN, but retain intact ILF, failed to induce Ag-specific IgA responses after oral immunization. These findings demonstrate that ILF are not essential for induction of intestinal IgA Ab responses to orally administered Ag. Furthermore, the induction of intestinal IgA Ab responses requires the proper maintenance of the MLN microarchitecture, including a follicular dendritic cell network.

IgA class switch occurs in the organized nasopharynx- and gut-associated lymphoid tissue, but not in the diffuse lamina propria of airways and gut.

Secretory IgA plays a crucial role in the host immune response as a first line of defense. A recent demonstration of in situ IgA class switching in intestinal lamina propria provided an opportunity to reconsider the model for the homing of IgA-committed B cells characterized by distinctive trafficking patterns to effector sites. Those effector sites depend on the organized mucosa-associated lymphoid tissues as their site of induction. In this report we show the preferential presence of IgM(+)B220(+) and IgA(+)B220(+) cells belonging to pre- and post-IgA isotype class-switched cells in the organized mucosa-associated lymphoid tissues, such as nasopharynx-associated lymphoid tissues, isolated lymphoid follicles, and Peyer's patches, and the defect of those populations in the diffuse effector tissues, such as the nasal passage and intestinal lamina propria. Consistent with these findings, the expressions of a series of IgA isotype class switch recombination-related molecules, including activation-induced cytidine deaminase, Ialpha-C micro circle transcripts, and Ialpha-C micro circle transcripts, were selectively detected in these organized mucosa-associated lymphoid structures, but not in the diffuse mucosal effector sites. Taken together, these findings suggest that IgA isotype class switching occurs only in the organized mucosa-associated lymphoid organs (e.g., nasopharynx-associated lymphoid tissues, isolated lymphoid follicles, and Peyer's patches), but not in the diffuse effector tissues of the upper respiratory and gastrointestinal tracts.