Peyer's patches are required for oral tolerance to proteins

Bronchus-associated lymphoid tissue (BALT) structure and function

Bronchus-associated lymphoid tissue (BALT) is a constitutive mucosal lymphoid tissue adjacent to major airways in some mammalian species, including rats and rabbits, but not humans or mice. A related tissue, inducible BALT (iBALT), is an ectopic lymphoid tissue that is formed upon inflammation or infection in both mice and humans and can be found throughout the lung. Both BALT and iBALT acquire antigens from the airways and initiate local immune responses and maintain memory cells in the lungs. Here, we discuss the development and function of BALT and iBALT in the context of pulmonary immunity to infectious agents, tumors, and allergens as well as autoimmunity and inflammatory diseases of the lung.

A combination of Flt3 ligand cDNA and CpG oligodeoxynucleotide as nasal adjuvant elicits protective secretory-IgA immunity to Streptococcus pneumoniae in aged mice

Our previous study showed that a combination of a plasmid-expressing Flt3 ligand (pFL) and CpG oligodeoxynucleotides (CpG ODN) as a combined nasal adjuvant elicited mucosal immune responses in aged (2-y-old) mice. In this study, we investigated whether a combination of pFL and CpG ODN as a nasal adjuvant for a pneumococcal surface protein A (PspA) would enhance PspA-specific secretory-IgA Ab responses, which could provide protective mucosal immunity against Streptococcus pneumoniae infection in aged mice. Nasal immunization with PspA plus a combination of pFL and CpG ODN elicited elevated levels of PspA-specific secretory-IgA Ab responses in external secretions and plasma in both young adult and aged mice. Significant levels of PspA-specific CD4(+) T cell proliferative and PspA-induced Th1- and Th2- type cytokine responses were noted in nasopharyngeal-associated lymphoreticular tissue, cervical lymph nodes, and spleen of aged mice, which were equivalent to those in young adult mice. Additionally, increased numbers of mature-type CD8, CD11b-expressing dendritic cells were detected in mucosal inductive and effector lymphoid tissues of aged mice. Importantly, aged mice given PspA plus a combination of pFL and CpG ODN showed protective immunity against nasal S. pneumoniae colonization. These results demonstrate that nasal delivery of a combined DNA adjuvant offers an attractive possibility for protection against S. pneumoniae in the elderly.

Active immunization using a single dose immunotherapeutic abates established EAE via IL-10 and regulatory T cells

Stimulation of Ag-specific inducible Treg can enhance resolution of autoimmune disease. Conventional methods to induce Treg often require induction of autoimmune disease or subjection to infection. Reovirus adhesin, protein σ1 (pσ1), can successfully facilitate tolerance when fused to a tolerogen. We tested whether myelin oligodendrocyte glycoprotein (MOG) fused to pσ1 (MOG-pσ1) can stimulate Ag-specific Treg. We show that C57BL/6 mice treated nasally with MOG-pσ1 fail to induce MOG-specific Abs and delayed-type hypersensitivity (DTH) responses and resist EAE. Such resistance was attributed to stimulation of Foxp3(+) Treg, as well as Th2 cells. MOG-pσ1's protective capacity was abrogated in IL-10(-/-) mice, but restored when adoptively transferred with MOG-pσ1-induced Treg. As a therapeutic, MOG-pσ1 diminished EAE within 24 h of nasal application, unlike recombinant MOG (rMOG), pσ1, or pσ1+rMOG, implicating the importance of Ag specificity by pσ1-based therapeutics. MOG-pσ1-treated mice showed elevated IL-4, IL-10, and IL-28 production by CD4(+) T cells, unlike rMOG treated or control mice that produced elevated IFN-γ or IL-17, respectively. These data show the feasibility of using pσ1 as a tolerogen platform for Ag-specific tolerance induction and highlight its potential use as an immunotherapeutic for autoimmunity.

Peyer's Patches: The Immune Sensors of the Intestine

The gut-associated lymphoid tissue (GALT) consists of isolated or aggregated lymphoid follicles forming Peyer's patches (PPs). By their ability to transport luminal antigens and bacteria, PPs can be considered as the immune sensors of the intestine. PPs functions like induction of immune tolerance or defense against pathogens result from the complex interplay between immune cells located in the lymphoid follicles and the follicle-associated epithelium. This crosstalk seems to be regulated by pathogen recognition receptors, especially Nod2. Although TLR exerts a limited role in PP homeotasis, Nod2 regulates the number, size, and T-cell composition of PPs, in response to the gut flora. In turn, CD4⁺ T-cells present in the PP are able to modulate the paracellular and transcellular permeabilities. Two human disorders, Crohn's disease and graft-versus-host disease are thought to be driven by an abnormal response toward the commensal flora. They have been associated with NOD2 mutations and PP dysfunction.

The role of the gut mucosal immunity in the development of tolerance against allergy to food

PURPOSE OF REVIEW

To provide an overview on the role of gut mucosal immunity in the development of tolerance against allergy to food.

RECENT FINDINGS

The gastrointestinal tract, through innate and specific immunologic factors, acts as a defense against ingested antigens. In addition to the mucous membrane integrity and digestion, numerous specific immunologic cells and mediators orchestrate such defensive mechanisms. In case of food antigens, the outcome is usually in favor of tolerance. Defects in that barrier, however, can lead to the development of aberrant immunologic responses, including hypersensitivity reactions.

SUMMARY

The prevailing evidence is that healthy mucosal immunity plus appropriate feeding regimen during early infancy are in favor of food tolerance. However, in addition to genetic predisposition, development of allergy is facilitated by defects in the gut barrier (immune or nonimmune) and the food allergen load.

Secretory-IgA antibodies play an important role in the immunity to Streptococcus pneumoniae

This study was designed to investigate whether secretory-IgA (S-IgA) Abs induced by a pneumococcal surface protein A (PspA)-based nasal vaccine are necessary for prevention of streptococcal colonization. Mice nasally immunized with PspA plus a plasmid expressing Flt3 ligand (pFL) cDNA as a mucosal adjuvant showed significantly higher levels of PspA-specific S-IgA and IgG Ab responses in both plasma and nasal washes when compared with naive mice. Although IgA(-/-) mice given nasal PspA plus pFL had significantly high levels of PspA-specific IgG Abs, high numbers of CFUs were detected in nasal washes and nasal passages. In contrast, vaccinated wild-type mice showed essentially no bacteria in the nasal cavity. Further, a nasal vaccine consisting of PspA plus pFL effectively reduced pre-existing Streptococcus pneumoniae in the nasal cavity. These results show that PspA-based vaccine-induced specific S-IgA Abs play a necessary role in the regulation of S. pneumoniae colonization in the nasal cavity.

Nanotechnology solutions for mucosal immunization

The current prevalence of infectious diseases in many developing regions of the world is a serious burden, impacting both the general health as well as economic growth of these communities. Additionally, treatment with conventional medication becomes increasingly challenging due to emergence of new and drug resistant strains jeopardizing the progress made in recent years towards control and elimination of certain types of infectious diseases. Thus, from a public health perspective, prevention such as through immunization by vaccination, which has proven to be most effective, might be the best alternative to prevent and combat infectious diseases in these regions. To achieve this, development of wide-scale immunization programs become necessary including vaccines that can easily and widely be distributed, stored and administered. Mucosal vaccines offer great potential since they can be administered via oral or intranasal delivery route which does not require trained personnel, avoids the use of needles and improves overall patient compliance and acceptance. However, it necessitates the implementation of specific immunization strategies to improve their efficacy. Application of nanotechnology to design and create particle mediated delivery systems that can efficiently encapsulate vaccine components for protection of the sensitive payload, target the mucosal immune system and incorporate mucosal adjuvants maximizing immune response is key strategy to improve the effectiveness of mucosal vaccines.

Different contributions of side-chains in beta-D-(1-->3,6)-galactans on intestinal Peyer's patch-immunomodulation by polysaccharides from Astragalus mongholics Bunge

Thirteen polysaccharides isolated from an extract of the aerial portions of Astragalus mongholics Bunge demonstrated immunomodulating activity against Peyer's patch immunocompetent cells. Nine of the active polysaccharide fractions were composed of either arabinogalactans, pectic arabinogalactans or pectins. The activities of the arabinogalactans and pectic arabinogalactans were associated with beta-D-(1-->3)-galactan moieties branched with beta-D-(1-->6)-galactooligosaccharide side-chains having degrees of polymerization of 8 or less. Degradation of the beta-D-(1-->3)-galactan or beta-D-(1-->6)-galactosyl side-chains in the arabinogalactans significantly decreased immunomodulating activity. Rhamnogalacturonan I (RG-I) with beta-D-(1-->3,6)-galactosyl side-chains having terminal beta-D-GlcA showed activity in the pectin-enriched fractions. Interestingly, the terminal GlcA was not required for activity of the arabinogalactan-enriched fractions, suggesting at least two different immunomodulating structures.

IL-28 supplants requirement for T(reg) cells in protein sigma1-mediated protection against murine experimental autoimmune encephalomyelitis (EAE)

Conventional methods to induce tolerance in humans have met with limited success. Hence, efforts to redirect tolerogen uptake using reovirus adhesin, protein sigma 1 (pσ1), may circumvent these shortcomings based upon the recent finding that when reovirus pσ1 is engineered to deliver chicken ovalbumin (OVA) mucosally, tolerance is obtained, even with a single dose. To test whether single-dose tolerance can be induced to treat EAE, proteolipid protein (PLP_130–151) was genetically fused to OVA to pσ1 (PLP:OVA-pσ1) and shown to significantly ameliorate EAE, suppressing proinflammatory cytokines by IL-10⁺ forkhead box P3 (FoxP3)⁺ CD25⁺CD4⁺ T_reg and IL-4⁺CD25⁻CD4⁺ Th2 cells. IL-10R or IL-4 neutralization reversed protection to EAE conferred by PLP:OVA-pσ1, and adoptive transfer of Ag-specific T_reg or Th2 cells restored protection against EAE in recipients. Upon assessment of each relative participant, functional inactivation of CD25 impaired PLP:OVA-pσ1's protective capacity, triggering TGF-β-mediated inflammation; however, concomitant inactivation of TGF-β and CD25 reestablished PLP:OVA-pσ1-mediated protection by IL-28-producing FoxP3⁺CD25⁻CD4⁺ T cells. Thus, pσ1-based therapy can resolve EAE independently of or dependently upon CD25 and assigns IL-28 as an alternative therapy for autoimmunity.

The epithelial gatekeeper against food allergy

The rapid rise of allergic disorders in developed countries has been attributed to the hygiene hypothesis, implicating that increased environmental sanitation in early childhood may be associated with higher incidence of hypersensitivity. Intestinal epithelial barriers play a crucial role in the maintenance of gut homeostasis by limiting penetration of luminal bacteria and dietary allergens, yet allowing antigen sampling via the follicle-associated epithelium for generation of tolerance. However, this intricate balance is upset in allergic intestines, whereby luminal proteins with antigenic properties gain access to the subepithelial compartment and stimulate mast cell degranulation. Recent studies demonstrated that food allergens were protected from lysosomal degradation, and were transported in large quantities across the epithelium by binding to cell surface IgE/CD23 (FcepsilonRII) that prevented the antigenic protein from lysosomal degradation in enterocytes. IL-4 (a Th2-type cytokine) not only increased production of IgE from B cells, but also upregulated the expression of CD23 on intestinal epithelial cells. Further studies indicated that CD23 was responsible for the bidirectional transport of IgE across epithelium. The presence of IgE/CD23 opens a gate for intact dietary allergens to transcytose across the epithelial cells, and thus foments the mast cell-dependent anaphylactic responses. The understanding of the molecular mechanism responsible for epithelial barrier defects may be helpful in designing novel therapies to treat food allergy and other allergic diseases.

Type II collagen oral tolerance; mechanism and role in collagen-induced arthritis and rheumatoid arthritis

Oral tolerance means a diminished immune response to previously fed antigens. Repeated oral administrations of type II collagen (CII) induce oral tolerance and inhibit the development of collagen-induced arthritis (CIA). Dendritic cells (DCs) in the gut-associated lymphoid tissue (GALT) take up the CII and then present it to T cells to generate regulatory T cells (Tregs), which induce systemic immune tolerance to CII. Inhibitory cytokines, such as transforming growth factor (TGF)-beta and interleukin (IL)-10, and several immune regulatory molecules, including indoleamine 2,3-dioxygenase (IDO) and retinoic acid, play an important role in Treg generation. Each DC subset may play different roles, and CD11c+CD11b+DCs and IDO+DCs are important in the generation of antigen-inducible Tregs in CII oral tolerance. Upon stimulation with the antigen involved in its generation, Treg is activated and regulates the immune response through inhibitory cytokine production, cell-to-cell contact-dependent mechanisms, DC modification, and bystander suppression. The DCs and Tregs are deeply involved in oral tolerance through reciprocal interactions. Several clinical trials have been conducted in RA patients to examine the efficacy of CII oral tolerance. An understanding the mechanism of oral tolerance to CII would give clinicians new insights into the development of natural immune tolerance and new therapeutic approaches for the treatment of autoimmune diseases.

Diverse immune responses to orally administered heat-killed cell preparation of Enterococcus faecalis strain EC-12 in murine immune tissues

Diverse immune responses to an orally administered heat-killed cell preparation of Enterococcus faecalis strain EC-12 (EC-12) among jejunal-Peyer's patches (PPs), ileal-PPs, mesenteric lymph nodes (MLNs), and spleen were compared by real-time PCR in mice. Intriguingly, distinct responses to EC-12 were observed in the various tissues. This study indicates a site-specific response to orally administered bacteria, particularly in jejunal- and ileal-PPs.

Atopic dermatitis and allergic reactions to individual fragrance chemicals

BACKGROUND

Allergic contact dermatitis prevalence is reported as equal in atopic and nonatopic dermatitis. Atopic dermatitis is under-represented in those with allergic contact dermatitis to agents having cutaneous and dietary exposure. We compared rates of atopic dermatitis between patients with allergic contact dermatitis arising out of individual fragrance chemicals with known oral/cutaneous exposure against exclusively cutaneous exposure.

METHODS

Between 1982 and 2007, 37 065 dermatitis patients were tested with Fragrance mix I. Those who were positive were tested for individual fragrance allergy. Chemicals were categorized according to whether their exposure pattern was solely cutaneous, oral or mixed. Current and past atopic dermatitis rates were compared between the whole population and groups allergic to individual fragrances. Age and gender were controlled.

RESULTS

Cinnamic alcohol and cinnamal allergy groups had reduced rates of both 'current' [24/266 (9.0%) P = 0.0008, 38/364 (10.4%) P = 0.0005] and 'past' atopic dermatitis [44/266 (16.5%) P = 0.009, 70/346 (19.2%) P = 0.037]. Atopic dermatitis rates in groups allergic to Evernia prunastri and hydroxycitronellal (cutaneous exposure only) were not reduced [120/597 (20.1%) and 41/153 (26.8%)]. Groups allergic to cinnamic alcohol (P < 0.0001, P < 0.0001) and cinnamal (P < 0.0001, P < 0.004) had reductions in 'current' and 'past' atopic dermatitis, compared with Evernia prunastri.

CONCLUSIONS

Patients allergic to individual fragrances with dietary exposure have reduced rates of atopic dermatitis. This suggests that patients with atopic dermatitis have heightened oral tolerance to dietary haptens, in contrast to the known close association of atopic dermatitis with food-protein allergy. Haptens may interfere with food protein tolerance by binding to soluble protein to alter its configuration and immunogenic profile.

Comparative analysis of mononuclear cells isolated from mucosal lymphoid follicles of the human ileum and colon

Studies of human mucosal lymphoid follicles are rare and have been limited to children's Peyer's patches, which are visible at endoscopy. We investigated lymphoid follicles in ileum biopsies of 87 patients and surgical colon specimens from 66 cancer patients, and examined phenotype and function of isolated follicular immune cells. Two (0-10) and 12 (0-117) follicles per patient were found in ileum and colon samples respectively (P < 0.001). The number of lymphoid follicles mononuclear cells (LFMC) that could be isolated per patient was higher from colon compared with ileum specimens [725 000 (0-23 Mio) versus 100 000 (0-1.3 Mio), P < 0.001]. T cells were predominant in both LFMC and lamina propria mononuclear cells (LPMC), but B cells were more and plasma cells less frequent in LFMC. T cells from mucosal follicles were more frequently CD4-positive and CD62L-positive, but less frequently CD8-positive, CD103-positive and CD69-positive than lamina propria T cells. LFMC from ileum compared with colon showed no differences in mononuclear cell composition. Anti-CD3/CD28 stimulation induced similar proliferation of LFMC and LPMC from ileum and colon, as well as secretion of high levels of interferon-gamma, tumour necrosis factor-alpha and interleukin (IL)-2, but lower levels of IL-4, IL-6 and IL-10. LFMC from colon secreted more IL-2 than those from ileum. Our study shows that mucosal lymphoid follicles can be identified clearly in adult human colon and yield viable immune cells sufficient for phenotypical and functional analysis. The cellular composition of LFMC from ileum and colon is similar, and both secrete predominantly T helper type 1 cytokines.

Does hapten exposure predispose to atopic disease? The hapten-atopy hypothesis

Contact allergy data indicates that atopics have heightened oral tolerance to haptens (chemical allergens). We speculate here, that artificially increased oral exposure to chemicals compete with dietary proteins for the development of oral tolerance, predisposing to the acquisition of food protein allergy and representing one driver for the increasing prevalence of protein allergy and/or atopy. Hapten exposure via other surfaces such as the skin and airways might also be important in promoting atopic disease. Consistent with this hypothesis it is notable that over 40 years, with the huge increase in atopic disease, there has also been an increase in dietary hapten exposure through processed food, formula milk and oral antibiotic and drug use.

A novel adenovirus expressing Flt3 ligand enhances mucosal immunity by inducing mature nasopharyngeal-associated lymphoreticular tissue dendritic cell migration

Previously, we showed that nasal administration of a naked cDNA plasmid expressing Flt3 ligand (FL) cDNA (pFL) enhanced CD4(+) Th2-type, cytokine-mediated mucosal immunity and increased lymphoid-type dendritic cell (DC) numbers. In this study, we investigated whether targeting nasopharyngeal-associated lymphoreticular tissue (NALT) DCs by a different delivery mode of FL, i.e., an adenovirus (Ad) serotype 5 vector expressing FL (Ad-FL), would provide Ag-specific humoral and cell-mediated mucosal immunity. Nasal immunization of mice with OVA plus Ad-FL as mucosal adjuvant elicited high levels of OVA-specific Ab responses in external secretions and plasma as well as significant levels of OVA-specific CD4(+) T cell proliferative responses and OVA-induced IFN-gamma and IL-4 production in NALT, cervical lymph nodes, and spleen. We also observed higher levels of OVA-specific CTL responses in the spleen and cervical lymph nodes of mice given nasal OVA plus Ad-FL than in mice receiving OVA plus control Ad. Notably, the number of CD11b(+)CD11c(+) DCs expressing high levels of costimulatory molecules was preferentially increased. These DCs migrated from the NALT to mucosal effector lymphoid tissues. Taken together, these results suggest that the use of Ad-FL as a nasal adjuvant preferentially induces mature-type NALT CD11b(+)CD11c(+) DCs that migrate to effector sites for subsequent CD4(+) Th1- and Th2-type cytokine-mediated, Ag-specific Ab and CTL responses.

Ovalbumin-protein sigma 1 M-cell targeting facilitates oral tolerance with reduction of antigen-specific CD4+ T cells

BACKGROUND & AIMS

The follicle-associated epithelium (FAE) plays key roles in antigen uptake and subsequent induction of mucosal immunity. In this study, we examined whether M-cell targeting using a protein antigen (Ag) delivery system would induce oral tolerance instead of enhancement of Ag-specific mucosal antibody (Ab) responses.

METHODS

Mice were fed different doses of a recombinant protein sigma 1 of reovirus genetically conjugated to ovalbumin (OVA-psigma1), psigma1 only, or phosphate-buffered saline (PBS) before oral challenge with OVA plus cholera toxin as mucosal adjuvant. OVA-specific Ab and CD4-positive (CD4(+)) T-cell responses were determined.

RESULTS

A low dose of OVA-psigma1 reduced anti-OVA Ab and CD4(+) T-cell responses in both mucosal and systemic lymphoid tissues. OVA/MHC I-A(d) tetramer staining showed that the numbers of OVA-specific CD4(+) T cells were significantly reduced in lamina propria of mice fed OVA-psigma1 than those fed psigma1 only or PBS only. In fact, Foxp3 expressing CD25(+) CD4(+) T cells were markedly increased in this tissue. Nonetheless, CD25(+) CD4(+) T cells from the spleen, mesenteric lymph nodes, and Peyer's patches of orally tolerized mice showed increased transforming growth factor beta1 (TGF-beta1) and interleukin-10 (IL-10) production compared with nontolerized mice.

CONCLUSIONS

These results show that an FAE M-cell targeting protein Ag delivery system facilitates oral tolerance induction because of a reduction in Ag-specific CD4(+) T cells and increased levels of TGF-beta1 and IL-10 producing, CD25(+) CD4(+) regulatory T cells in both systemic and mucosal lymphoid tissues.

Reduced frequency of atopic dermatitis in quinoline-allergic patients: the 'hapten-atopy hypothesis'

BACKGROUND

While allergy to food proteins is almost exclusively found in association with atopy, it has been our experience that contact allergy to some contact allergens/haptens with both cutaneous and gastrointestinal exposures is reduced in atopic dermatitis (AD) patients as a group.

OBJECTIVE

To assess the contact allergy rates of two classes of antimicrobial haptens, one with both cutaneous and gastrointestinal exposures (quinolines) and one with only significant cutaneous exposure (aminoglycosides), with respect to the presence or absence of AD.

METHODS

Contact allergy rates to neomycin (aminoglycoside) and quinoline mix/clioquinol in patients attending the St John's Institute of Dermatology for diagnostic patch testing were retrospectively analysed; current AD and history of AD were noted.

RESULTS

In comparison to neomycin-allergic subjects, there was a highly significant negative association between quinoline contact allergy and current presence of AD (P = 0.0028); negative association between quinoline contact allergy and a history of AD did not reach significance (P = 0.07).

CONCLUSIONS

In comparison to an antimicrobial with no significant gastrointestinal exposure (neomycin), contact allergy to quinolines is negatively associated with the presence of AD. This is in contrast to food protein allergy, which is strongly associated with atopy. Possible explanations could include (i) confounding factors or (ii) AD patients are efficient at orally tolerizing haptens and inefficient at orally tolerizing proteins, secondary to their atopic status or (iii) oral tolerance of haptens antagonizes tolerance of food proteins and also leads to an immunological shift towards atopy (hapten-atopy hypothesis).

Low-dose tolerance is mediated by the microfold cell ligand, reovirus protein sigma1

Mucosal tolerance induction generally requires multiple or large Ag doses. Because microfold (M) cells have been implicated as being important for mucosal tolerance induction and because reovirus attachment protein sigma1 (psigma1) is capable of binding M cells, we postulated that targeting a model Ag to M cells via psigma1 could induce a state of unresponsiveness. Accordingly, a genetic fusion between OVA and the M cell ligand, reovirus psigma1, termed OVA-psigma1, was developed to enhance tolerogen uptake. When applied nasally, not parenterally, as little as a single dose of OVA-psigma1 failed to induce OVA-specific Abs even in the presence of adjuvant. Moreover, the mice remained unresponsive to peripheral OVA challenge, unlike mice given multiple nasal OVA doses that rendered them responsive to OVA. The observed unresponsiveness to OVA-psigma1 could be adoptively transferred using cervical lymph node CD4(+) T cells, which failed to undergo proliferative or delayed-type hypersensitivity responses in recipients. To discern the cytokines responsible as a mechanism for this unresponsiveness, restimulation assays revealed increased production of regulatory cytokines, IL-4, IL-10, and TGF-beta1, with greatly reduced IL-17 and IFN-gamma. The induced IL-10 was derived predominantly from FoxP3(+)CD25(+)CD4(+) T cells. No FoxP3(+)CD25(+)CD4(+) T cells were induced in OVA-psigma1-dosed IL-10-deficient (IL-10(-/-)) mice, and despite showing increased TGF-beta1 synthesis, these mice were responsive to OVA. These data demonstrate the feasibility of using psigma1 as a mucosal delivery platform specifically for low-dose tolerance induction.

The Peyer's patch is a critical immunoregulatory site for mucosal tolerance in experimental autoimmune encephalomylelitis (EAE)

Expression of MCP-1 in the central nervous system (CNS) is associated with various neuroinflammatory diseases, including multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). In this study, we found that MCP-1 was decreased in the CNS but increased in the gut following oral administration of myelin basic protein (MBP) correlating with protection from EAE. To study the trafficking and the fate of T cells during oral tolerance, MBP-specific TCR transgenic (Tg) CD4(+) T cells were labeled using 5,6-carboxy-succinimidyl-fluorescein-ester (CFSE) and transferred intravenously to syngeneic B10.PL recipients before feeding with either MBP or PBS. We observed that the CFSE-labeled T cells traffic to the peripheral lymphoid tissue and the Peyer's patches (PP). The labeled T cells proliferate in vivo in both the lymph node and the PP 48h after MBP feeding, but the cells are maintained in the PP longer than in the LN. CFSE-labeled cells in the PP have high levels of CD69 and Fas expression which is accompanied by increased apoptosis after MBP feeding. Our observations suggest that oral administration of autoantigen induces an elevation of MCP-1 in the gut, early T cell trafficking and activation in the periphery and the PP, followed by deletion of autoreactive T cells in the PP.

Tolerance in the absence of autoantigen

Regulatory T (T(reg)) cells show promise for treating autoimmune diseases, but their induction to elevated potency has been problematic when the most optimally derived cells are from diseased animals. To circumvent reliance on auto-antigen reactive T(reg) cells, stimulation to vaccine antigens (Ags) may offer a viable alternative while maintaining potency to protect against proinflammatory diseases. Our Salmonella vaccine expressing colonization factor Ag I (CFA/I) possesses anti-inflammatory properties, evident by elevated Th2 cell responses, reduced inflammatory cell infiltrates in the Peyer's patches, and an absence of proinflammatory cytokine production by infected macrophages. Given these findings, we hypothesized whether this vaccine would be protective against experimental autoimmune encephalomyelitis (EAE). As such, Salmonella-CFA/I protected in both prophylactic and therapeutic paradigms against proteolipid protein (PLP(139-151))-mediated EAE in SJL mice. The protected mice showed significantly reduced clinical disease and subsequent resolution when compared to PBS-treated controls. Histopathological studies showed reduced demyelination and no inflammation of spinal cords when compared to PBS- or Salmonella vector-treated mice. To ascertain whether the observed immune deviation was in part supported by T(reg) cells, analysis revealed involvement of FoxP3(+) CD25(+) CD4(+) T cells. Adoptive transfer of induced TGF-beta (+) T(reg) cells from vaccinated mice showed complete protection against PLP(139-151) challenge, but not by naive T(reg) cells. Partial protection to EAE was also achieved by the adoptive transfer of CD25(-) CD4(+) T cells, suggesting that Th2 cells also contributed. Thus, these data show that T(reg) cells are induced by oral vaccination with Salmonella-CFA/I contributing to the efficacious treatment of autoimmune disease.

Regulatory role of Peyer’s patches for the inhibition of OVA-induced allergic diarrhea

Intestinal allergic diseases are initiated by aberrant Th2-type immune responses, including elevation of IgE antibodies (Abs) and infiltration of eosinophils. However, little is known about the role of Peyer's patches (PP) in the control of allergic diseases. Using a mouse model for food allergy, we here show that mice lacking PP are more susceptible to disease development and show higher levels of antigen-specific IgE Abs than do PP-intact mice. In our study, we noted that high numbers of eosinophils infiltrated into the small intestine of PP-null mice. In contrast, the PP of intact mice contained regulatory CD4+CD25+ Foxp3+ T cells (Treg) that are known to produce high levels of IL-10, and inhibited the development of allergic diarrhea. PP-intact mice thus developed allergic diarrhea when treated with anti-CD25 or anti-IL-10 monoclonal antibody (mAb) in vivo. These studies demonstrate that PP, as the site where IL-10-producing Treg cells are created, mediate the mucosal regulatory network for the control of undesired allergic responses in the intestine.

Digestion, Absorption and Tissue Distribution of Ovalbumin and Palmitoyl-ovalbumin: Impact on Immune Responses Triggered by Orally Administered Antigens

Previous work in this laboratory has demonstrated that ovalbumin coupled to palmitoyl residues (palmitoyl-Ova) does not induce oral tolerance. The present study sought to determine whether this coupling affects digestion, absorption and transfer of antigen. Ova and palmitoyl-Ova were shown to be digested differently in vitro by proteolytic enzymes and presented different tissue distribution kinetics after being labelled with (99m)technetium and orally administered to animals. Palmitoyl-Ova remained longer in the stomach, while native Ova was quickly transferred to the gut and other organs. After 3 h, higher levels of palmitoyl-Ova were found in the blood, Peyer's patches, mesenteric lymph nodes, liver and, especially, the spleen, which appears to be essential for immunization with palmitoyl-Ova. In fact, splenectomized mice treated orally with palmitoyl-Ova became tolerant, while tolerance to Ova was not affected. Thus, palmitoyl coupling was demonstrated to affect antigen digestion, absorption and transport. This is the first time that the spleen has been shown to be required for oral immunization with palmitoyl-Ova.

The importance of regional lymph nodes for mucosal tolerance

The immune system is organized as a number of distinct lymphoid organs interconnected by recirculating lymphocytes. These organs, such as lymph nodes, spleen, and gut-associated Peyer's patches, are compartmentalized, providing separate niches for T and B cells. In addition, regional compartmentalization of lymphoid organs themselves exists, leading to the distinction between the mucosal and the systemic immune systems. This distinction not only reflects the anatomical localization but also is based on functional differences, with predominant tolerance induction via mucosal routes and immunity seen after systemic antigen exposure. These differences are associated with regional differences in the lymphoid organs and with environmental conditions of the tissues in which the immune system functions. Recirculation patterns of lymphocytes differ between mucosal and systemic lymphoid organs, and more insight into the mechanisms that imprint this behavior has been generated recently. Differences in dendritic cells have been observed between mucosal and systemic sites, and knowledge on how local factors contribute to the immune system is emerging. From our studies on mucosal tolerance in mouse models, it has become evident that regional lymph nodes draining the mucosa are important sites to direct immune responses. Here, we discuss the way regional lymph nodes contribute to the direction of immune responses and what is known about the local factors and cell behavior that form the basis for these differences.

Immune privilege in the gut: the establishment and maintenance of non-responsiveness to dietary antigens and commensal flora

Immune privilege in the gut is the result of a complex interplay between the gut microbiome, gut luminal antigens, and the intestinal epithelial barrier. Composed of both physical and immunochemical components, the intestinal barrier secretes immunoregulatory mediators that promote the generation of tolerogenic antigen-presenting cells, phagocytic innate immune cells characterized by 'inflammatory anergy', and regulatory cells of the adaptive immune system. Innate immune cells mediate controlled transepithelial transport of luminal antigens as far as the mesenteric lymph nodes, where the intestinal and peripheral immune systems intersect. This promotes the generation of adaptive regulatory lymphocytes that actively suppress effector cell responses against gut luminal antigens and flora. The net result is the generation of tolerance to dietary antigens and the maintenance of gut homeostasis. Dysregulation of this complex immunoregulatory network leads to diseases such as food allergy and inflammatory bowel disease. Future therapies for these diseases will likely involve the functional restoration of the barrier and regulatory cell functions at the epithelial/luminal interface.

Initiating mechanisms of food allergy: Oral tolerance versus allergic sensitization

Immediately after birth the mucosa of the gastrointestinal tract, which represents the greatest body surface area exposed to the outside environment, is confronted with a large variety of foreign antigens. The immune system of the intestine now has to meet the task of discriminating between pathogens and harmless antigens, such as food proteins and commensal bacteria, and to respond accordingly. This important job is fulfilled by cells of the gut-associated lymphoid tissue, the largest immunologic organ in the body. Despite the large extent of food antigen exposure, only a small percentage of individuals experience adverse immunologic reactions to food. This is due to the fact that the normal immune response to dietary proteins is associated with the induction of oral tolerance, which refers to a state of active inhibition of immune responses to an antigen by means of prior exposure to that antigen via the oral route. Abrogation of oral tolerance or failure to induce oral tolerance may result in the development of food hypersensitivity. In the present review, factors that may play a role in the outcome of oral tolerance versus sensitization to food proteins are discussed.

Animal models of food allergy: opportunities and barriers

The potential for animal models to mimic the human disease process makes them an attractive tool for determining disease mechanisms, predicting disease triggers, and testing treatment regimens. With this in mind, animal models of food allergy have been receiving increasing attention as research tools to answer some of the difficult questions regarding food-allergy disease. Most of the food-allergy animal models developed to date have been designed to test reagents for immunotherapeutic treatment of allergic disease and to predict the potential human allergenicity of proteins. Current animal models under development are rodent, swine, and dog. The variables affecting development of such models include allergen concentration, allergen matrix or food source, allergen route of exposure, duration, animal age, adjuvant use, and dose range of allergens. Each model presents opportunities for and barriers to a fuller understanding of the allergic response. The conditions inherent to each model and the intended purpose of the study should therefore be considered prior to its use.

Peyer's patches are required for the induction of rapid Th1 responses in the gut and mesenteric lymph nodes during an enteric infection

The Peyer's patches (PP) and mesenteric lymph nodes (MLN) are structural components of the gut-associated lymphoid tissues and contribute to the induction of immune responses toward infection in the gastrointestinal tract. These secondary lymphoid organs provide structural organization for efficient cellular interactions and the initiation of primary adaptive immune responses against infection. Immunity against primary infection with the enteric apicomplexan parasite, Eimeria vermiformis, depends on the rapid induction of local Th1 responses. Lymphotoxin (LT)-deficient mice which have various defects in secondary lymphoid organs were infected with E. vermiformis. The relative susceptibility of LTalpha(-/-), LTbeta(-/-), LTalpha(+/-)beta(+/-) mice and bone marrow chimeras, indicated that rapid protective Th1 responses required both PP and MLN. Moreover, the timing of Th1 induction in both MLN and gut was dependent on the presence of PP suggesting a level of cooperation between immune responses induced in these distinct lymphoid structures. The delay in Th1 induction was attributable to the delayed arrival of a broad range of dendritic cell subsets in the MLN and a substantial reduction of CD8alpha(-)CD11b(high) B220(-) dendritic cells in PP-deficient mice.

Intestinal and pulmonary mucosal T cells: local heroes fight to maintain the status quo

Mucosal immunity in the lung and intestine is controlled by complex multifaceted systems. While mucosal T cells are essential for protection against invading pathogens owing to their proximity to the outside world, powerful systems must also be in place to harness ongoing inflammatory processes. In each site, distinct anatomical structures play key roles in mounting and executing both protective and deleterious mucosal T cell responses. Although analogies can be drawn regarding the immune systems of these two organs, there are substantial dissimilarities necessitated by unique physiologic constraints. Here, we discuss how T cell activation and effector function are generated in the mucosae.

Importance of gastrointestinal ingestion and macromolecular antigens in the vein for oral tolerance induction

Oral administration of a certain dose of antigen can generally induce immunological tolerance against the same antigen. In this study, we showed the temporal appearance of ovalbumin (OVA) antigens in both portal and peripheral blood of mice after the oral administration of OVA. Furthermore, we detected 45,000 MW OVA in mouse serum 30 min after the oral administration of OVA. Based on this observation, we examined whether the injection of intact OVA into the portal or peripheral vein induces immunological tolerance against OVA. We found that the intravenous injection of intact OVA did not induce immunological tolerance but rather enhanced OVA-specific antibody production in some subclasses, suggesting that OVA antigens via the gastrointestinal tract but not intact OVA may contribute to establish immunological tolerance against OVA. Therefore, we examined the effects of digesting intact OVA in the gastrointestinal tract on the induction of oral tolerance. When mice were orally administered or injected into various gastrointestinal organs, such as the stomach, duodenum, ileum, or colon and boosted with intact OVA, OVA-specific antibody production and delayed-type hypersensitivity (DTH) response were significantly enhanced in mice injected into the ileum or colon, compared with orally administered mice. These results suggest that although macromolecular OVA antigens are detected after oral administration of OVA in tolerant-mouse serum, injection of intact OVA cannot contribute to tolerance induction. Therefore, some modification of macromolecular OVA in the gastrointestinal tract and ingestion may be essential for oral tolerance induction.

Antigen-induced, tolerogenic CD11c+,CD11b+ dendritic cells are abundant in Peyer's patches during the induction of oral tolerance to type II collagen and suppress experimental collagen-induced arthritis

OBJECTIVE

Although oral tolerance is a well-known phenomenon, the role of dendritic cells (DCs) is not well characterized. This study was conducted to better understand the differential role played by each Peyer's patch DC subset in the induction of oral tolerance to type II collagen (CII) in murine collagen-induced arthritis (CIA).

METHODS

CII was fed 6 times to DBA/1 mice beginning 2 weeks before immunization, and the effect on arthritis was assessed. We compared the proportion of CD11c+,CD11b+ DCs and CD11c+,CD8alpha+ DCs in the Peyer's patches of CII-fed tolerized and phosphate buffered saline-fed nontolerized mice after the induction of CIA. The immunosuppressive properties of each DC subset were determined using fluorescence-activated cell sorter analysis for intracellular interleukin-10 (IL-10) and IL-12 and mixed lymphocyte culture. The ability of each DC subset to induce CD4+,CD25+ T regulatory cells was also examined. Mice were injected with CII-pulsed CD11c+,CD11b+ DCs isolated from Peyer's patches of tolerized mice, and the effect on CIA was examined.

RESULTS

The severity of arthritis was significantly lower in tolerized mice. The proportion of CD11c+,CD11b+ DCs was increased in the Peyer's patches of tolerized mice and those DCs exhibited immunosuppressive characteristics, such as increased IL-10 production, inhibition of T cell proliferative responses to CII, and CD4+,CD25+ regulatory T cell induction. Furthermore, the CD11c+,CD11b+ DCs suppressed the severity of arthritis upon adoptive transfer.

CONCLUSION

Our observations demonstrate that CD11c+,CD11b+ DCs, which are abundant in Peyer's patches during the induction of oral tolerance to CII, are crucial for the suppression of CIA and could be exploited for immunotherapy of autoimmune diseases.

Low zone tolerance induced by systemic application of allergens inhibits Tc1-mediated skin inflammation

BACKGROUND

The induction of tolerance may be a promising target of strategies aimed at preventing harmful allergic diseases. Low zone tolerance (LZT), induced by epicutaneous application of low doses of contact allergens, inhibits the development of T(C)1-mediated contact hypersensitivity (CHS).

OBJECTIVE

We evaluated the effect of systemic (oral, intravenous) administration of low amounts of haptens on specific immune reactions and tolerance induction.

METHODS

By using the mouse model of LZT, we analyzed immune reactions in vivo (skin inflammation) and T-cell responses in vitro after oral, intravenous, or epicutaneous application of low amounts of the contact allergen 2,4,6-trinitro-1-chlorobenzene (TNCB).

RESULTS

Subimmunogenic doses of TNCB applied orally and intravenously induced a significant tolerance reaction in vivo comparable to epicutaneously tolerized mice, indicating that LZT is a systemically mediated tolerance reaction. In vitro analysis in all models of LZT revealed the generation of IL-10 secreting, regulatory CD4+ T cells that were absolutely required for the development of hapten-specific CD8+ T(C)2 cells. Adoptive transfer experiments identified CD8+ T(C)2 cells as effector T cells of LZT inhibiting the development of CHS-promoting T(C)1 cells and consequently the manifestation of CHS. These suppressor CD8+ T(C)2 cells were found as well in skin-draining as in mesenteric lymph nodes and in the spleen of tolerized animals independent of the route of tolerization.

CONCLUSION

These data indicate that systemic uptake and presentation of small amounts of haptens (eg, contact allergens, drugs, metals) induce the development of LZT and thus prevent inappropriate activation of the immune system and protect from allergic diseases.

CLINICAL IMPLICATIONS

These findings will be of particular importance because tolerance induction by protocols applying subimmunogenic, low amounts of haptens may be used as tools for immunotherapy in allergic and autoimmune diseases.

T cell-mediated oral tolerance is intact in germ-free mice

Commensal enteric bacteria stimulate innate immune cells and increase numbers of lamina propria and mesenteric lymph node (MLN) T and B lymphocytes. However, the influence of luminal bacteria on acquired immune function is not understood fully. We investigated the effects of intestinal bacterial colonization on T cell tolerogenic responses to oral antigen compared to systemic immunization. Lymphocytes specific for ovalbumin-T cell receptor (OVA-TCR Tg(+)) were transplanted into germ-free (GF) or specific pathogen-free (SPF) BALB/c mice. Recipient mice were fed OVA or immunized subcutaneously with OVA peptide (323-339) in complete Freund's adjuvant (CFA). Although the efficiency of transfer was less in GF recipients, similar proportions of cells from draining peripheral lymph node (LN) or MLN were proliferating 3-4 days later in vivo in GF and SPF mice. In separate experiments, mice were fed tolerogenic doses of OVA and then challenged with an immunogenic dose of OVA 4 days later. Ten days after immunization, lymphocytes were restimulated with OVA in vitro to assess antigen-specific proliferative responses. At both high and low doses of OVA, cells from both SPF and GF mice fed OVA prior to immunization had decreased proliferation compared to cells from control SPF or GF mice. In addition, secretion of interferon (IFN)-gamma and interleukin (IL)-10 by OVA-TCR Tg(+) lymphocytes was reduced in both SPF and GF mice fed OVA compared to control SPF or GF mice. Unlike previous reports indicating defective humoral responses to oral antigen in GF mice, our results indicate that commensal enteric bacteria do not enhance the induction of acquired, antigen-specific T cell tolerance to oral OVA.

The development of the mucosal immune system pre- and post-weaning: balancing regulatory and effector function

The mucosal immune system fulfils the primary function of defence against potential pathogens that may enter across vulnerable surface epithelia. However, a secondary function of the intestinal immune system is to discriminate between pathogen-associated and 'harmless' antigens, expressing active responses against the former and tolerance to the latter. Control of immune responses appears to be an active process, involving local generation of IgA and of regulatory and/or regulated T lymphocytes. Two important periods of maximum exposure to novel antigens occur in the young animal, immediately after birth and at weaning. In both cases the antigenic composition of the intestinal contents can shift suddenly, as a result of a novel diet and of colonisation by novel strains and species of bacteria. Changes in lifestyles of man, and husbandry of animals, have resulted in weaning becoming much more abrupt than previously in evolution, increasing the number of antigens that must be simultaneously evaluated by neonates. Thus, birth and weaning are likely to represent hazard and critical control points in the development of appropriate responses to pathogens and harmless dietary and commensal antigens. Neonates are born with relatively undeveloped mucosal immune systems. At birth this factor may prevent both expression of active immune responses and development of tolerance. However, colonisation by intestinal flora expands the mucosal immune system in antigen-specific and non-specific ways. At weaning antibody to fed proteins can be detected, indicating active immune responses to fed proteins. It is proposed that under normal conditions the ability of the mucosal immune system to mount active responses to foreign antigens develops simultaneously with the ability to control and regulate such responses. Problems arise when one or other arm of the immune system develops inappropriately, resulting in inappropriate effector responses to harmless food proteins (allergy) or inadequate responses to pathogens (disease susceptibility).

Inhalation Tolerance Is Induced Selectively in Thoracic Lymph Nodes but Executed Pervasively at Distant Mucosal and Nonmucosal Tissues

Under immunogenic conditions, both the site of initial Ag exposure and consequent T cell priming in specific draining lymph nodes (LNs) imprint the ensuing immune response with lasting tissue-selective tropism. With respect to immune tolerance, whether the site of tolerance induction leads to compartmentalized or, alternatively, pervasive tolerance has not been formally investigated. Using a murine model of inhalation tolerance, we investigated whether the induction of respiratory mucosal tolerance precludes the development of de novo Th2 sensitization upon subsequent exposure to the same Ag at distant mucosal (gut) and nonmucosal (cutaneous) sites. By tracking the proliferation of CFSE-labeled OVA-TCR transgenic CD4(+) T cells upon OVA inhalation in vivo, we defined the site of tolerance induction to be restricted to the thoracic LNs. Expectedly, inhalation tolerance prevented de novo Th2 sensitization upon subsequent exposure to the same Ag at the same site. Importantly, although gut- and skin-draining LNs were not used during tolerance induction, de novo Ag-specific proliferation and Th2 differentiation in these LNs, as well as memory/effector Th2 responses in the gut (allergic diarrhea) and skin (late-phase cutaneous responses) were inhibited upon immunogenic challenge to the same Ag. Interestingly, this pervasive tolerogenic phenotype was not associated with the presence of suppressive activity throughout the lymphatics; indeed, potent suppressive activity was detected solely in the spleen. These data indicate that while inhalation tolerance is selectively induced in local thoracic LNs, its tolerogenic activity resides systemically and leads to pervasive immune tolerance in distant mucosal and nonmucosal sites.

A rice-based edible vaccine expressing multiple T cell epitopes induces oral tolerance for inhibition of Th2-mediated IgE responses

Peptide immunotherapy using multiple predominant allergen-specific T cell epitopes is a safe and promising strategy for the control of type I allergy. In this study, we developed transgenic rice plants expressing mouse dominant T cell epitope peptides of Cry j I and Cry j II allergens of Japanese cedar pollen as a fusion protein with the soybean seed storage protein glycinin. Under the control of the rice seed storage protein glutelin GluB-1 promoter, the fusion protein was specifically expressed and accumulated in seeds at a level of 0.5% of the total seed protein. Oral feeding to mice of transgenic rice seeds expressing the T cell epitope peptides of Cry j I and Cry j II before systemic challenge with total protein of cedar pollen inhibited the development of allergen-specific serum IgE and IgG antibody and CD4(+) T cell proliferative responses. The levels of allergen-specific CD4(+) T cell-derived allergy-associated T helper 2 cytokine production of IL-4, IL-5, and IL-13 and histamine release in serum were significantly decreased. Moreover, the development of pollen-induced clinical symptoms was inhibited in our experimental sneezing mouse model. These results indicate the potential of transgenic rice seeds in production and mucosal delivery of allergen-specific T cell epitope peptides for the induction of oral tolerance to pollen allergens.

Induction of mucosal and systemic immune responses against human carcinoembryonic antigen by an oral vaccine

Carcinoembryonic antigen (CEA) is a tumor-associated antigen targeted for the development of colorectal tumor vaccines. In this study, we developed papillomavirus pseudoviruses encoding the truncated CEA without NH2-terminal signal peptide (PV-CEA) as an oral vaccine to induce CEA-specific CTL responses. In CEA transgenic (CEA-Tg) mice orally immunized with PV-CEA, the immunologic tolerance to CEA as a "self-antigen" was overcome and both mucosal and systemic CEA-specific cytolytic activities were detected by in vitro 51Cr release assays. In a tumor prevention model, the growth rate of CEA+ tumors was significantly delayed in CEA-Tg mice orally immunized with PV-CEA when compared with the control vaccine. Further, the IFN-gamma enzyme-linked ImmunoSPOT and in vitro 51Cr release assay results showed that HLA-A2-restricted, CEA-specific CTL responses were induced in both mucosal and systemic lymphoid tissues in A2 transgenic mice after oral immunization with PV-CEA. Finally, we showed that coadministration of papillomavirus pseudoviruses encoding interleukin-2 with PV-CEA enhanced the generation of A2-restricted, CEA-specific CTLs in aged CEA/A2 double transgenic mice, which were more clinically relevant. Our data suggest that PV-CEA pseudovirus vaccine is a promising oral CEA vaccine for humans to induce CEA-specific CTLs at the site of colorectal tumors (i.e., intestinal mucosa), which might efficiently eliminate CEA+ colorectal tumor cells in the mucosa.

The influence of environment on development of the mucosal immune system

The mucosal immune system expresses active responses against pathogens and also tolerance against harmless food and commensal bacterial antigens. The mechanisms that determine which of these outcomes occur after recognition of antigens by T-cells are not clear. One possibility is that it is determined by the initial interaction between a dendritic and a naïve T-cell in organised lymphoid tissue. However, such organised structures are, evolutionarily, quite recent and the original immune system must have made appropriate responses in more diffuse immunological architecture; a second possibility is that the critical interaction is between primed T-cells and their environment, in the lamina propria of the intestine. The mucosal immune system of neonates is poorly developed and inefficient at expressing appropriate immune responses. Development is influenced by a range of environmental factors including maternally derived antigen or antibody and commensal flora and pathogens. The intestine is a complex immunological structure in which the immune system and the macro- and microenvironment interact.

Organizing a mucosal defense

Gastrointestinal associated lymphoid tissue can be divided into loosely organized effector sites, which include the lamina propria and intraepithelial lymphocytes, and more organized structures, such as mesenteric lymph nodes (LNs), Peyer's patches (PPs), isolated lymphoid follicles, and cryptopatches (CPs). These organized structures in the gastrointestinal tract have been hypothesized to play the role of primary lymphoid organ, supporting the extrathymic development of T lymphocytes (CPs), secondary lymphoid organs involved in the induction of the mucosal immune response (PPs), and tertiary lymphoid structures whose function is still under debate (isolated lymphoid follicles). The most widely studied lymphoid structure found in the small intestine is the PP. PPs are secondary lymphoid structures, and their development and function have been extensively investigated. However, single lymphoid aggregates resembling PPs have been also described in humans and in the murine small intestines. These isolated lymphoid follicles have both germinal centers and an overlying follicle-associated epithelium, suggesting that they also can function as inductive sites for the mucosal immune response. This review compares and contrasts the development and function of the four main organized gastrointestinal lymphoid tissues: CPs, isolated lymphoid follicles, PPs, and mesenteric LNs.

Induction of mucosal tolerance in Peyer's patch-deficient, ligated small bowel loops

To explore the requirement for M cells and the Peyer's patch (PP) in induction of oral tolerance and address the potential in vivo role of intestinal epithelial cells as nonprofessional APCs, we have attempted to induce tolerance in mice with ligated small bowel loops without M cells and Peyer's patches. A 2-centimeter section of vascularized small bowel was spliced away from the gut without disruption of the mesenteric attachments. We introduced OVA directly into the lumen of the loop prior to footpad immunization. By excising segments of bowel that contain PPs in some mice and segments without patches in others, we could study the necessity of the M cell and the underlying patch versus epithelial cells in induction of mucosal tolerance. We show that OVA-specific T cell proliferation and serum antibody responses are reduced in mice that have previously been given OVA both in PP-containing loops and in loops without patches. Furthermore, both high- and low-dose tolerance could be induced in the absence of PPs. Low-dose tolerance is associated with bystander suppression and requires IL-10, which indicates active suppression and the induction of regulatory cells. These data suggest that there is a critical role for components of the mucosal immune system other than PPs in antigen sampling and induction of oral tolerance.

Immunomodulatory dendritic cells in intestinal lamina propria

The lamina propria (LP) of the small intestine contains many dendritic cells (DC), which are likely to be in close contact with luminal antigens, but their role in intestinal immune responses has been overlooked. Here we show that after feeding mice ovalbumin (OVA), the majority of antigen uptake is associated with DC in the small intestinal LP, and we describe the isolation, purification and initial characterization of theses DC. We obtained >90% CD11c(+) DC using magnetic cell sorting, of which the majority were CD11b(+)CD8alpha(-), with smaller numbers of CD11b(-)CD8alpha(+) and CD11b(-)CD8alpha(-) DC as well as a distinct population of CD11c(int)class II MHC(lo) B220(+) DC. Freshly isolated LP DC expressed variable but generally low levels of CD40, CD80 and CD86, which were up-regulated by activation with LPS. LP DC were endocytic in vivo and in vitro and could present antigen to OVA-specific CD4(+) T cells in vitro. Antigen-loaded LP DC from OVA-fed mice also primed specific CD4(+) T cells in vivo and in vitro, but adoptive transfer of these DC into naive recipients induced hyporesponsiveness to subsequent challenge. LP DC also expressed significant levels of mRNA for IL-10 and type I IFN, but not IL-12, suggesting they may play a central and unique role in immune homeostasis in the gut.