Amplification of the secretory IgA response to Toxoplasma gondii using cholera toxin

Our study demonstrates that cholera toxin (CT) markedly enhances the intestinal anti-T. gondii antibody response following oral immunisation of mice with a T. gondii sonicate (TSo) and CT. The antibodies induced were mostly IgA and secretory IgA but a small quantity of IgG was also produced. In contrast, no intestinal anti-T. gondii IgM antibodies were detected. Anti-CT IgA antibodies were also present in intestinal secretions but in much lower quantities than the T. gondii-specific IgA. No anti-CT IgG nor IgM antibodies were detected. Western blot analysis showed that CT induced not only an increase of the intensity of the intestinal IgA antibody response to the 30-kDa band but also induced intestinal IgA antibodies against other major T. gondii proteins (p22, and the 28-kDa antigen) as recognised by specific monoclonal antibodies. The amplification of the anti-T. gondii secretory IgA response by means of an appropriate adjuvant may be one major step leading towards an orally induced immune protection against toxoplasmosis.     

Generalized systemic and mucosal immunity in mice after mucosal stimulation with cholera toxin

Cholera toxin (CT) has been found to be an extremely potent immunogen for mucosal IgA responses when administered via the intestine. This study has examined both mucosal and systemic immune responses after feeding CT and compared these responses with those obtained after feeding keyhole limpet hemocyanin (KLH), another protein that is strongly immunogenic in mice. Feeding CT to mice resulted not only in IgA antibody in intestinal secretions but also resulted in substantial plasma IgG and IgA antibody levels. Feeding KLH in much larger quantity resulted in little or no antibody response in intestinal secretions or plasma. Lymphoid cells from various tissues of mice fed CT were cultured in vitro for 10 days and the supernatant was tested for antibody to CT. Spontaneous antibody synthesis (no antigen added to cultures) was present in cultures of each cell type, but IgG anti-CT was found mainly in cultures of spleen and mesenteric lymph node cells and IgA anti-CT mainly in cultures of Peyer's patch and lamina propria cells. Peyer's patch cells cultured with CT as antigen synthesized both IgG and IgA anti-CT, suggesting that the antibody response to both isotypes originated in this site. Helper T cell activity for both IgA and IgG anti-CT was detected in spleens, mesenteric lymph nodes, and Peyer's patches. Lastly, when KLH and CT were fed to mice at the same time, an intestinal IgA anti-KLH and plasma IgG anti-KLH response was stimulated, a response pattern similar to that occurring to CT after CT was fed alone. We conclude that mucosal stimulation by CT generates both a systemic IgG and mucosal IgA response to this antigen, and that CT can cause a similar pattern of response to an unrelated protein antigen when both are administered into the intestine at the same time. The data favor the idea that both the IgG and IgA responses originate in GALT and then disseminate to other tissues. We propose that CT accomplishes these effects by altering the regulatory environment within GALT.     

Protection of the villus epithelial cells of the small intestine from rotavirus infection does not require immunoglobulin A

Immunoglobulin A (IgA) is the primary immune response induced in the intestine by rotavirus infection, but vaccination with virus-like particles induces predominantly IgG, not IgA. To definitively assess the role of IgA in protection from rotavirus infection, IgA knockout mice, which are devoid of serum and secretory IgA, were infected and then rechallenged with murine rotavirus at either 6 weeks or 10 months. Following primary rotavirus infection, IgA knockout mice cleared virus as effectively as IgA normal control mice. Rotavirus-infected IgA knockout mice produced no serum or fecal IgA but did have high levels of antirotavirus serum IgG and IgM and fecal IgG, whereas IgA normal control mice made both serum IgA and IgG and fecal IgA. Both IgA normal and IgA knockout mice were totally protected from rotavirus challenge at 42 days. Ten months following a primary infection, both IgA normal and knockout mice still had high levels of serum and fecal antirotavirus antibody and were totally protected from rotavirus challenge. To determine if compensatory mechanisms other than IgG were responsible for protection from rotavirus infection in IgA knockout mice, mice were depleted of CD4(+) T cells or CD8(+) T cells. No changes in the level of protection were seen in depleted mice. These data show that fecal or systemic IgA is not essential for protection from rotavirus infection and suggest that in the absence of IgA, IgG may play a significant role in protection from mucosal pathogens.     

Relative Importance of Rotavirus-Specific Effector and Memory B Cells in Protection against Challenge

Adult BALB/c mice were orally inoculated with murine (strain EDIM), simian (strain RRV), or bovine (strain WC3) rotavirus. Six or 16 weeks after inoculation, mice were challenged with EDIM. At the time of challenge and in the days immediately following challenge, production of rotavirus-specific immunoglobulin A (IgA), IgG, and IgM by small intestinal lamina propria lymphocytes (LPL) was determined by fragment culture, and quantities of virus-specific antibodies at the intestinal mucosal surface were determined by intestinal lavage. Mice immunized with EDIM were completely protected against EDIM challenge both 6 and 16 weeks after immunization. Protection was associated with production of high levels of IgA by LPL and detection of virus-specific IgA at the intestinal mucosal surface. In addition, animals immunized and later challenged with EDIM did not develop a boost in antibody responses, suggesting that they were also not reinfected. We also found that in mice immunized with nonmurine rotaviruses, (i) quantities of virus-specific IgA generated following challenge were greater 16 weeks than 6 weeks after immunization, (ii) immunization enhanced the magnitude but did not hasten the onset of production of high quantities of virus-specific IgA by LPL after challenge, and (iii) immunization induced partial protection against challenge; however, protection was not associated with either production of virus-specific antibodies by LPL or detection of virus-specific antibodies at the intestinal mucosal surface.     

Strong differential regulation of serum and mucosal IgA responses as revealed in CD28-deficient mice using cholera toxin adjuvant

In this study, we show that costimulation required for mucosal IgA responses is strikingly different from that needed for systemic responses, including serum IgA. Following oral immunization with cholera toxin (CT) adjuvant we found that whereas CTLA4-H1 transgenic mice largely failed to respond, CD28-/- mice developed near normal gut mucosal IgA responses but poor serum Ab responses. The local IgA response was functional in that strong antitoxic protection developed in CT-immunized CD28-/- mice. This was in spite of the fact that no germinal centers (GC) were observed in the Peyer's patches, spleen, or other peripheral lymph nodes. Moreover, significant somatic hypermutation was found in isolated IgA plasma cells from gut lamina propria of CD28-/- mice. Thus, differentiation to functional gut mucosal IgA responses against T cell-dependent Ags does not require signaling through CD28 and can be independent of GC formations and isotype-switching in Peyer's patches. By contrast, serum IgA responses, similar to IgG-responses, are dependent on GC and CD28. However, both local and systemic responses are impaired in CTLA4-Hgamma1 transgenic mice, indicating that mucosal IgA responses are dependent on the B7-family ligands, but require signaling via CTLA4 or more likely a third related receptor. Therefore, T-B cell interactions leading to mucosal as opposed to serum IgA responses are uniquely regulated and appear to represent separate events. Although CT is known to strongly up-regulate B7-molecules, we have demonstrated that it acts as a potent mucosal adjuvant in the absence of CD28, suggesting that alternative costimulatory pathways are involved.     

Partial IgA-deficiency with increased Th2-type cytokines in TGF-beta 1 knockout mice.

Though it has been shown that TGF-beta 1 directs B cells to switch to IgA in vitro, no studies have assessed TGF-beta 1 effects on mucosal vs systemic immunity in vivo. When the B cell functions of TGF-beta 1 gene-disrupted (TGF-beta 1-/-) mice were analyzed, significantly decreased IgA levels and increased IgG and IgM levels in serum and external secretions were observed. Further, analysis of Ab forming cells (AFC) isolated from both mucosal and systemic lymphoid tissue showed elevated IgM, IgG, and IgE, with decreased IgA AFC. A lack of IgA-committed B cells was seen in TGF-beta 1-/- mice, especially in the gastrointestinal (GI) tract. Splenic T cells triggered via the TCR expressed elevated Th2-type cytokines and, consistent with this observation, a 31-fold increase in serum IgE was seen in TGF-beta 1-/- mice. Thus, uncontrolled B cell responses, which include elevated IgE levels, a lack of antiinflammatory IgA, and an excess of complement-binding IgG and IgM Abs, will promote inflammation at mucosal surfaces in TGF-beta 1-/- mice and likely contribute to pulmonary and GI tract lesions, ultimately leading to the early death of these mice.     

Oral and parenteral immunization with HIV immunosome induce the secretion of IgA specific of HIV-1 in the salivary and the production of circulatory IgA in mice and rabbits]

Given the sexual transmission of HIV, the establishment of a genital mucosal immunity through secretory IgA may be necessary to achieve protection. We have investigated if repeated stimulations of oral mucosa with HIV-Immunosomes would lead to the production of secretory IgA in saliva and also, if such an oral immunization could prime the immune system to an early systemic immune response following a parenteral immunisation with a low dose of the antigen. HIV-1 gp 160-specific secretory IgA were detected in the saliva of all rabbits orally immunized with HIV-Immunosomes. As early as one week after the parenteral immunization, high titers of serum IgA, IgM and IgG were detected both in mice and rabbits that had been orally stimulated with the antigen. These antibodies could neutralize HIV infectivity in vitro. Animals that were immunized only parenterally showed a very weak humoral immune response.     

Mucosal B cell deficiency in IgA-/- mice abrogates the development of allergic lung inflammation

We have investigated the consequence of lack of IgA on host immunity using a murine model of allergic lung inflammation. Mice with a targeted disruption of the alpha-switch region and 5' H chain gene (IgA(-/-) mice), which lack total IgA, developed significantly reduced pulmonary inflammation with fewer inflammatory cells in lung tissue and bronchoalveolar lavage fluids, as well as reduced levels of total and IgG1 OVA-specific Abs and decreased IL-4 and IL-5 in bronchoalveolar lavage fluids compared with IgA(+/+) controls, following allergen sensitization and challenge. This defect was attributable to fewer B cells in the lungs of IgA(-/-) mice. Polymeric IgR-deficient (pIgR(-/-)) mice, which lack the receptor that transports polymeric IgA across the mucosal epithelium where it is cleaved to form secretory IgA, were used to assess the contribution of secretory IgA vs total IgA in the induction of allergic lung inflammation. pIgR(-/-) and pIgR(+/+) mice had comparable levels of inflammation, demonstrating that IgA bound to secretory component is not necessary for the development of allergic lung inflammation, although this does not necessarily rule out a role for transudated IgA in lung secretions because of "mucosal leakiness" in these mice. The results indicate that Ag-specific B cells are required at mucosal surfaces for induction of inflammation and likely function as major APCs in the lung for soluble protein Ags.     

Mucosal immunity to influenza without IgA: an IgA knockout mouse model

IgA knockout mice (IgA-/-) were generated by gene targeting and were used to determine the role of IgA in protection against mucosal infection by influenza and the value of immunization for preferential induction of secretory IgA. Aerosol challenge of naive IgA-/- mice and their wild-type IgA+/+ littermates with sublethal and lethal doses of influenza virus resulted in similar levels of pulmonary virus infection and mortality. Intranasal and i.p. immunization with influenza vaccine plus cholera toxin/cholera toxin B induced significant mucosal and serum influenza hemagglutinin-specific IgA Abs in IgA+/+ (but not IgA-/-) mice as well as IgG and IgM Abs in both IgA-/- and IgA+/+ mice; both exhibited similar levels of pulmonary and nasal virus replication and mortality following a lethal influenza virus challenge. Monoclonal anti-hemagglutinin IgG1, IgG2a, IgM, and polymeric IgA Abs were equally effective in preventing influenza virus infection in IgA-/- mice. These results indicate that IgA is not required for prevention of influenza virus infection and disease. Indeed, while mucosal immunization for selective induction of IgA against influenza may constitute a useful approach for control of influenza and other respiratory viral infections, strategies that stimulate other Igs in addition may be more desirable.     

Nasal Immunization of Mice with Human Papillomavirus Type 16 Virus-Like Particles Elicits Neutralizing Antibodies in Mucosal Secretions

To specifically induce a mucosal antibody response to purified human papillomavirus type 16 (HPV16) virus-like particles (VLP), we immunized female BALB/c mice orally, intranasally, and/or parenterally and evaluated cholera toxin (CT) as a mucosal adjuvant. Anti-HPV16 VLP immunoglobulin G (IgG) and IgA titers in serum, saliva, and genital secretions were measured by enzyme-linked immunosorbent assay (ELISA). Systemic immunizations alone induced HPV16 VLP-specific IgG in serum and, to a lesser extent, in genital secretions but no secretory IgA. Oral immunization, even in the presence of CT, was inefficient. However, three nasal immunizations with 5 μg of VLP given at weekly intervals to anesthetized mice induced high (>10⁴) and long-lasting (>15 weeks) titers of anti-HPV16 VLP antibodies in all samples, including IgA and IgG in saliva and genital secretions. CT enhanced the VLP-specific antibody response 10-fold in serum and to a lesser extent in saliva and genital secretions. Nasal immunization of conscious mice compared to anesthetized mice was inefficient and correlated with the absence of uptake of a marker into the lung. However, a 1-μg VLP systemic priming followed by two 5-μg VLP intranasal boosts in conscious mice induced both HPV16 VLP-specific IgG and IgA in secretions, although the titers were lower than in anesthetized mice given three intranasal immunizations. Antibodies in serum, saliva, and genital secretions of immunized mice were strongly neutralizing in vitro (50% neutralization with ELISA titers of 65 to 125). The mucosal and systemic/mucosal HPV16 VLP immunization protocols that induced significant titers of neutralizing IgG and secretory IgA in mucosal secretions in mice may be relevant to genital HPV VLP-based human vaccine trials.     

Genetic control of the murine immune response to cholera toxin

This study was undertaken to determine whether previously noted differences in the immune response of inbred strains of mice to cholera toxin (CT) might be under immune response gene control. A series of inbred, congenic, and intra-H-2I region recombinant mouse strains were tested for responsiveness to CT after i.p. immunization with 0.1 micrograms CT in alum. Samples of plasma were collected at intervals before and after priming and boosting. IgG and IgA anti-CT were measured by ELISA. In three different sets of congenic strains, the level of IgG anti-CT clearly depended on the H-2 haplotype of the strain rather than on any background or Igh genes. Strains with the H-2b and H-2q haplotypes were high responders, and strains with the H-2k, H-2s and H-2d haplotypes were low responders. Within the H-2 complex, the IgG anti-CT response was mapped to the I-A subregion with the use of congenic intra-H-2I region recombinant strains. In contrast to these results with IgG anti-CT, plasma IgA anti-CT levels were uniformly low and indeterminate. We conclude that the murine IgG anti-CT response is controlled by a locus within the I-A subregion of H-2--a remarkable finding, considering the known abilities of this toxin to bind to and to directly stimulate lymphocytes.     

Facilitated production of secretory IgA against Shiga toxin B subunits by intranasal application of antigen-coated polystyrene microspheres

We examined the effects of microspheres as antigen carriers in mucosal immunization. Shiga toxin B subunits (Stx1B) were adsorbed on 6 mum polystyrene microspheres, which were then intranasally administered to mice together with cholera toxin (CT). Stx1B-specific serum IgG production and secretory IgA production at local mucosal sites were enhanced by the use of microspheres. When OVA was used as a model antigen, secretory IgA production but not serum IgG production was enhanced on the use of microspheres. These results indicated that microspheres provide a useful means of potentiating the immune response against Stx1B with weak immunogenicity.     

Neutralization of cholera toxin by rat IgA secretory antibodies induced by a free synthetic peptide

Secretory immunoglobulin A (sIgA) is the major immunoglobulin in the bile of several species. They contribute to local immune defences of the gut. The protection against cholera toxin (CT) is due to the presence of specific sIgA in the bile and in the gut. We have already reported that oral administration of the peptide corresponding to the sequence 50-75 of cholera toxin B subunit elicits serum antibodies neutralizing CT activity, and that IgA and local protection are observed in the intestine of P50-75 orally immunized mice. In this study, we demonstrate the potential of this synthetic peptide as immunogen without carrier or adjuvant, not only in a strain known to be sensitive to CT, but also in an outbred one. Furthermore, this peptide stimulates the mucosal immunity, since we show that P50-75 induced-sIgA purified from rats bile and serum, are capable of neutralizing CT activity in the in vivo intestinal ligated loop test.     

An important role for polymeric Ig receptor-mediated transport of IgA in protection against Streptococcus pneumoniae nasopharyngeal carriage

The importance of IgA for protection at mucosal surfaces remains unclear, and in fact, it has been reported that IgA-deficient mice have fully functional vaccine-induced immunity against several bacterial and viral pathogens. The role of respiratory Ab in preventing colonization by Streptococcus pneumoniae has now been examined using polymeric IgR knockout (pIgR(-/-)) mice, which lack the ability to actively secrete IgA into the mucosal lumen. Intranasal vaccination with a protein conjugate vaccine elicited serotype-specific anti-capsular polysaccharide Ab locally and systemically, and pIgR(-/-) mice produced levels of total serum Ab after vaccination that were similar to wild-type mice. However, pIgR(-/-) mice had approximately 5-fold more systemic IgA and 6-fold less nasal IgA Ab than wild-type mice due to defective transport into mucosal tissues. Wild-type, but not pIgR(-/-) mice were protected against infection with serotype 14 S. pneumoniae, which causes mucosal colonization but does not induce systemic inflammatory responses in mice. The relative importance of secretory IgA in host defense was further shown by the finding that intranasally vaccinated IgA gene-deficient mice were not protected from colonization. Although secretory IgA was found to be important for protection against nasal carriage, it does not appear to have a crucial role in immunity to systemic pneumococcus infection, because both vaccinated wild-type and pIgR(-/-) mice were fully protected from lethal systemic infection by serotype 3 pneumococci. The results demonstrate the critical role of secretory IgA in protection against pneumococcal nasal colonization and suggest that directed targeting to mucosal tissues will be needed for effective vaccination in humans.     

Targeted deletion of the IgA constant region in mice leads to IgA deficiency with alterations in expression of other Ig isotypes

A murine model of IgA deficiency has been established by targeted deletion of the IgA switch and constant regions in embryonic stem cells. B cells from IgA-deficient mice were incapable of producing IgA in vitro in response to TGF-beta. IgA-deficient mice expressed higher levels of IgM and IgG in serum and gastrointestinal secretions and decreased levels of IgE in serum and pulmonary secretions. Expression of IgG subclasses was complex, with the most consistent finding being an increase in IgG2b and a decrease in IgG3 in serum and secretions. No detectable IgA Abs were observed following mucosal immunization against influenza; however, compared with those in wild-type mice, increased levels of IgM Abs were seen in both serum and secretions. Development of lymphoid tissues as well as T and B lymphocyte function appeared normal otherwise. Peyer's patches in IgA-deficient mice were well developed with prominent germinal centers despite the absence of IgA in these germinal centers or intestinal lamina propria. Lymphocytes from IgA-deficient mice responded to T and B cell mitogens comparable to those of wild-type mice, while T cells from IgA-deficient mice produced comparable levels of IFN-gamma and IL-4 mRNA and protein. In conclusion, mice with targeted deletion of the IgA switch and constant regions are completely deficient in IgA and exhibit altered expression of other Ig isotypes, notably IgM, IgG2b, IgG3, and IgE, but otherwise have normal lymphocyte development, proliferative responses, and cytokine production.     

Role of immunoglobulin A in protection against reovirus entry into Murine Peyer's patches

Reovirus type 1 Lang (T1L) infects the mouse intestinal mucosa by adhering specifically to epithelial M cells and exploiting M-cell transport to enter the Peyer's patches. Oral inoculation of adult mice has been shown to elicit cellular and humoral immune responses that clear the infection within 10 days. This study was designed to determine whether adult mice that have cleared a primary infection are protected against viral entry upon oral rechallenge and, if so, whether antireovirus secretory immunoglobulin A (S-IgA) is a necessary component of protection. Adult BALB/c mice that were orally inoculated on day 0 with reovirus T1L produced antiviral S-IgA in feces and IgG in serum directed primarily against the reovirus sigma1 attachment protein. Eight hours after oral reovirus challenge on day 21, the Peyer's patches of previously exposed mice contained no detectable virus whereas Peyer's patches of naive controls contained up to 2,300 PFU of reovirus/mg of tissue. Orally inoculated IgA knockout (IgA(-/-)) mice cleared the initial infection as effectively as wild-type mice and produced higher levels of reovirus-specific serum IgG and secretory IgM than C57BL/6 wild-type mice. When IgA(-/-) mice were rechallenged on day 21, however, their Peyer's patches became infected. These results indicate that intestinal S-IgA is an essential component of immune protection against reovirus entry into Peyer's patch mucosa.     

Impairment of mucosal immunity by total parenteral nutrition: requirement for IgA in murine nasotracheal anti-influenza immunity

Secretory IgA (SIgA) is the primary mucosal Ig and has been shown to mediate nasotracheal (NT) mucosal immunity in normal immune BALB/c mice. This finding has been challenged by a report of NT immunity without IgA in knockout mice, suggesting that IgA may not be necessary for the protection of mucosal surfaces. Although other protective mechanisms may become active in the congenital absence of SIgA, these mechanisms are not the primary means of protection in normal mice. In this paper we show that feeding chemically defined total parenteral nutrition (TPN) to genetically normal, immune ICR mice by the i.v. route results in loss of nasal anti-influenza immunity and a significant drop in influenza-specific SIgA in the upper respiratory tract compared with chow-fed mice (p < 0.005), while the serum influenza-specific IgG titer is unaffected. Loss of upper respiratory tract mucosal immunity is not related to serum Ab, because 10 of 13 TPN-fed mice shed virus into their nasal secretions despite adequate serum anti-influenza IgG titers. The number of IgG Ab-secreting cells in the nasal passages and spleens of TPN-fed mice was unaffected, while both the number and the percentage of splenic IgA-secreting cells were decreased relative to those in chow-fed animals. The loss of immunity is due to the route of nutrition, not the composition of the diet, because TPN solution fed orally via gastrostomy instead of i.v. maintains NT anti-influenza mucosal immunity. We hypothesize that delivery of nutrition via the gut triggers the release of gastrointestinal neuropeptides necessary for maintenance of the mucosal immune system.     

Intranasal immunization with a lipooligosaccharide-based conjugate vaccine from nontypeable Haemophilus influenzae enhances bacterial clearance in mouse nasopharynx

Nontypeable Haemophilus influenzae (NTHi) is a major cause of otitis media in children. We investigated whether intranasal immunization with a detoxified lipooligosaccharide-tetanus toxoid (dLOS-TT) conjugate vaccine would generate protective immunity against NTHi in a mouse model of nasopharyngeal clearance. The results demonstrated that intranasal immunization with dLOS-TT plus adjuvant cholera toxin (CT) significantly induced LOS-specific IgA antibodies in mouse external secretions, especially in nasal wash (90-fold), bronchoalveolar lavage fluid (25-fold), saliva (13-fold) and fecal extract (three-fold). LOS-specific IgA antibody-forming cells were also found in mucosal and lymphoid tissues with their highest numbers in the nasal passage (528 per 10(6) cells). In addition, the intranasal immunization elicited a significant rise in LOS-specific IgG (32-fold) and IgA (13-fold) in serum. For the immunized mice which had been challenged through the nose with 10(7) live NTHi strain 9274 cells, the vaccine group showed a significant reduction (74-77%) of NTHi, compared to that of control groups with CT alone or dLOS plus CT (P<0.05). Negative correlations were found between bacterial counts and the levels of nasal wash IgA or IgG, saliva IgA and serum IgG. The clearance of five heterologous strains was investigated and revealed a significant clearance of strains 3198, 5657 and 7502 but not of strains 1479 and 2019. These data suggest that intranasal immunization with dLOS-TT vaccine elicits both mucosal and systemic immunity against NTHi and enhances bacterial clearance from nasopharynx in mice. Such a vaccine and vaccination regime may be applicable to humans with an appropriate formulation.     

Polymeric immunoglobulin receptor in intestinal immune defense against the lumen-dwelling protozoan parasite Giardia

The polymeric Ig receptor (pIgR) is conserved in mammals and has an avian homologue, suggesting evolutionarily important functions in vertebrates. It transports multimeric IgA and IgM across polarized epithelia and is highly expressed in the intestine, yet little direct evidence exists for its importance in defense against common enteric pathogens. In this study, we demonstrate that pIgR can play a critical role in intestinal defense against the lumen-dwelling protozoan parasite Giardia, a leading cause of diarrheal disease. The receptor was essential for the eradication of Giardia when high luminal IgA levels were required. Clearance of Giardia muris, in which IgA plays a dominant role, was severely compromised in pIgR-deficient mice despite significant fecal IgA output at 10% of normal levels. In contrast, eradication of the human strain Giardia lamblia GS/M, for which adaptive immunity is less IgA dependent in mice, was unaffected by pIgR deficiency, indicating that pIgR had no physiologic role when lower luminal IgA levels were sufficient for parasite elimination. Immune IgA was greatly increased in the serum of pIgR-deficient mice, conferred passive protection against Giardia, and recognized several conserved giardial Ags, including ornithine carbamoyltransferase, arginine deiminase, alpha-enolase, and alpha- and beta-giardins, that are also detected in human giardiasis. Corroborative observations were made in mice lacking the J chain, which is required for pIgR-dependent transepithelial IgA transport. These results, together with prior data on pIgR-mediated immune neutralization of luminal cholera toxin, suggest that pIgR is essential in intestinal defense against pathogenic microbes with high-level and persistent luminal presence.     

Heterologous protection induced by the inner capsid proteins of rotavirus requires transcytosis of mucosal immunoglobulins

Protective immunization against rotavirus (RV) can be achieved with heterologous RV, i.e., virus isolated from another species, and with heterologous inner core VP2 and VP6 proteins assembled as virus-like particles (VLP). Although the antigenically conserved VP6 protein does not induce in vitro-neutralizing antibodies, it may, however, elicit immunoglobulins (Ig) involved in heterologous protection, as some IgA against VP6 prevent RV infection in a backpack mouse model. The protective role of Ig directed to the RV inner core proteins VP2 and VP6 was investigated in J-chain-deficient mice (J chain(-/-)), which have a defect in the polymeric Ig receptor (pIgR)-mediated transcytosis of IgA and IgM. J chain(-/-) mice and wild-type (WT) mice were intranasally vaccinated with bovine RV-derived VLP2/6 and then challenged with highly infectious murine ECw RV. Whereas WT mice were totally protected, immunized J chain(-/-) mice shed RV for several days. In addition, na?ve J chain(-/-) mice exhibited a 2-day delay in clearing RV compared with WT mice. The immunized J chain(-/-) mice displayed unaltered VLP2/6-specific B-cell numbers in spleen and in mesenteric nodes and similar levels of serum anti-VLP2/6 Ig, confirming that the adaptive B-cell response is preserved in J chain(-/-) mice. These results indicate that J-chain-mediated transcytosis of Ig participates in the clearance of RV and that epithelial pIgR-mediated transport of Ig is involved in the heterologous protection induced by VLP2/6.