Glucocorticoid regulation of the humoral immune system. I. In vivo effects of dexamethasone on IgA and IgG in serum and at mucosal surfaces

The present studies were undertaken to determine whether glucocorticoids influence the levels of Ig in serum, saliva, and vaginal secretions. When measured by RIA, IgA levels in serum were elevated when increasing doses of dexamethasone, a potent synthetic glucocorticoid, were administered to intact- and adrenalectomized-ovariectomized rats. In contrast, IgA levels decreased in saliva and vaginal secretions over the same dose range. Time course studies indicated that the decline in salivary IgA, observed at 24 h after a single injection of dexamethasone, preceded a rise in serum IgA detected at 24 h after the second hormone treatment. Both responses were maximal at day 2 and did not change with further hormone exposure. After immunization and boosting with SRBC at two mucosal sites (intestinal Peyer's patch and uterine lumen), dexamethasone increased anti-SRBC IgA antibody levels in serum and reduced their presence in vaginal secretions. In contrast, anti-SRBC IgG-antibody levels in serum and vaginal secretions were reduced with hormone treatment. In the absence of hormone treatment, pooled sera from nonimmunized animals, when analyzed by HPLC, contained polymeric and dimeric IgA that was present in roughly equal proportion. In response to dexamethasone, polymeric IgA increased to a greater extent than did monomeric IgA. In summary, these studies demonstrate that dexamethasone alters the levels of IgA as well as specifically directed IgA and IgG antibodies in secretions and serum. Further, it suggests that glucocorticoid controlled IgA increases in serum and decreases in vaginal and salivary secretions may be due, in part, to a redistribution of polymeric IgA from mucosal surfaces to serum.     

In vivo response of secretory component in the rat uterus to antigen, IFN-gamma, and estradiol

Intrauterine immunization of ovariectomized rats with SRBC is known to elicit pronounced IgA and IgG antibody responses in uterine secretions of immunized uteri. To determine whether secretory component (SC), the receptor for transporting polymeric IgA from tissues to mucosal surfaces, was also influenced by Ag, ovariectomized rats were immunized and boosted by placing SRBC into the lumena of individual uterine horns. In response to Ag, the levels of polymeric IgA, as well as free SC and SC bound to polymeric IgA, increased in uterine secretions. When ovariectomized animals were treated with estradiol, a fivefold increase in SC levels was observed in the immunized horns, indicating that a hormone response is superimposed on the Ag-induced stimulation of uterine SC. To determine whether IFN-gamma influences the presence of SC in uterine secretions, IFN-gamma was placed in the uterine lumena of ovariectomized nonimmunized rats. When uterine secretions were analyzed, significantly higher levels of SC were found in IFN-gamma-exposed uteri than were present in saline treated control animals. In contrast, intrauterine instillation of IFN-gamma had no effect on the levels of IgA in uterine secretions. This response was specific for IFN-gamma in that IFN-alpha/beta had no effect on uterine SC or IgA levels. These results indicate that intrauterine instillation of Ag, in addition to evoking pronounced antibody responses, stimulates the production of SC, which may be responsible for the transport of polymeric IgA from tissue to uterine secretions. Furthermore, they indicate that IFN-gamma placed in the uterine lumen stimulates SC production and suggest that the uterine SC response to Ag may be mediated by the action of IFN-gamma on uterine epithelial cells.     

Estradiol regulation of the secretory immune system in the female reproductive tract: IgA in uterine and vaginal secretions of rats following portacaval anastomosis

The uterine immune system is under the control of estradiol which acts to increase the levels of both IgA and secretory component (SC) in uterine secretions. The objective of the present study was to determine whether serum is the primary source of the IgA which enters uterine secretions in response to estradiol. To examine this, serum IgA levels in rats were surgically elevated by portacaval anastomosis which prevents hepatic clearance of IgA. Under these conditions, IgA levels in serum were 2- to 4-fold higher than those of intact or sham-operated animals. Levels of IgA in uterine secretions of portacaval animals, however, were significantly lower than those measured in controls when animals were ovariectomized and treated with estradiol. IgA in vaginal secretions of portacaval animals was greater than that in sham-operated or intact rats. To determine whether IgA had leaked from the uterus into vaginal secretions, a second group of animals had their uteri ligated at the utero-cervical junction prior to hormone treatment. Following estradiol stimulation, uterine IgA levels in portacaval animals were the same as those measured in intact and sham-operated animals. When free SC was measured in uterine secretions of ligated rats, levels were the same in all three groups. These studies indicate that elevated levels of serum IgA did not lead to a rise in uterine IgA. Further, since SC, which is thought to be a receptor for transporting IgA into mucosal secretions, remained unchanged, it appears unlikely that IgA movement into the uterine lumen was transport limited. These studies suggest that the presence of IgA in uterine and vaginal secretions is not due exclusively to serum contributions but may involve local synthesis of IgA.     

Secretory immunoglobulin A antibodies against the sigma1 outer capsid protein of reovirus type 1 Lang prevent infection of mouse Peyer's patches

Reovirus type 1 Lang (T1L) adheres to M cells in the follicle-associated epithelium of mouse intestine and exploits the transport activity of M cells to enter and infect the Peyer's patch mucosa. Adult mice that have previously cleared a reovirus T1L infection have virus-specific immunoglobulin G (IgG) in serum and IgA in secretions and are protected against reinfection. Our aim in this study was to determine whether secretory IgA is sufficient for protection of Peyer's patches against oral reovirus challenge and, if so, against which reovirus antigen(s) the IgA may be directed. Monoclonal antibodies (MAbs) of the IgA isotype, directed against the sigma1 protein of reovirus T1L, the viral adhesin, were produced and tested along with other, existing IgA and IgG MAbs against reovirus T1L outer capsid proteins. Anti-sigma1 IgA and IgG MAbs neutralized reovirus T1L in L cell plaque reduction assays and inhibited T1L adherence to L cells and Caco-2(BBe) intestinal epithelial cells in vitro, but MAbs against other proteins did not. Passive oral administration of anti-sigma1 IgA and IgG MAbs prevented Peyer's patch infection in adult mice, but other MAbs did not. When anti-sigma1 IgA and IgG MAbs were produced in mice from hybridoma backpack tumors, however, the IgA prevented Peyer's patch infection, but the IgG did not. The results provide evidence that neutralizing IgA antibodies specific for the sigma1 protein are protective in vitro and in vivo and that the presence of these antibodies in intestinal secretions is sufficient for protection against entry of reovirus T1L into Peyer's patches.     

Differential induction of mucosal and systemic antibody responses in women after nasal,rectal, or vaginal immunization: influence of the menstrual cycle

A cholera vaccine containing killed vibrios and cholera toxin B subunit (CTB) was used to compare mucosal immunization routes for induction of systemic and mucosal Ab. Four groups of women were given three monthly immunizations by the rectal immunization (R(imm)) route, nasal immunization (N(imm)) route, or vaginal immunization route during either the follicular (V-FP(imm)) or luteal (V-LP(imm)) menstrual cycle phase. N(imm) was performed with 10-fold less vaccine to determine if administration of less Ag by this route can, as in rodents, produce mucosal Ab responses comparable to those induced by higher dose R(imm) or vaginal immunization. Concentrations of Ab induced in sera and secretions were measured by ELISA. None of these routes produced durable salivary Ab responses. N(imm) induced greatest levels of CTB-specific IgG in sera. R(imm) failed to generate CTB-specific IgA in genital tract secretions. N(imm), V-FP(imm), and V-LP(imm) all produced cervical CTB-specific IgA responses comparable in magnitude and frequency. However, only V-FP(imm) induced cervical IgA2-restricted Ab to the bacterial LPS vaccine component. V-FP(imm), but not V-LP(imm), also induced CTB-specific IgA in rectal secretions. N(imm) was superior to V-FP(imm) for producing rectal CTB-specific IgA, but the greatest amounts of CTB-specific IgA and LPS-specific IgA, IgG, and IgM Ab were found in rectal secretions of R(imm) women. These data suggest that in women, N(imm) alone could induce specific Ab in serum, the genital tract, and rectum. However, induction of genital tract and rectal Ab responses of the magnitude generated by local V-FP(imm) or R(imm) will likely require administration of comparably high nasal vaccine dosages.     

A comparison of antibody titres in mouse uterine fluid after immunization by several routes, and the effect of the uterus on antibody titres in vaginal fluid

Measurements of specific antibody titres in uterine fluid of mice immunized by different routes indicated that two immunizations in the pelvic presacral space using aluminium hydroxide as adjuvant was a simple and effective way to elicit a significant IgA and IgG response. Higher IgA and IgG titres were produced in uterine fluid by subcutaneous immunization with antigen in Freund's complete adjuvant followed by intravaginal boosting without adjuvant, but this immunization involved both a toxic adjuvant and repeated applications of large doses of antigen in the vagina. Intragastric immunization produced an IgA response in the uterus but no IgG. Local intravaginal priming and boosting with large doses of antigen without adjuvant produced an IgA response in uterine fluid, but was less effective for IgG and was inefficient in terms of time and the amount of antigen used. Hysterectomy reduced the concentration of specific IgA in vaginal fluid of immunized mice to no more than 5% of normal, indicating that most of the IgA in vaginal fluid originates in the uterus. In contrast, IgG titres were not significantly different in hysterectomized and intact mice. IgA titres in vaginal fluid were at least partly restored to normal levels in sham-hysterectomized mice.     

Estradiol and progesterone regulation of immunoglobulin A and G and secretory component in cervicovaginal secretions of the rat

The present study examined the influence of hormones on the levels of immunoglobulins A (IgA) and G (IgG) and secretory component (SC) in cervicovaginal secretions of ovariectomized rats. Administration of estradiol to ovariectomized rats resulted in a significant decline in cervicovaginal content of IgA, IgG and SC. This response was dose dependent and was not prevented by administration of dexamethasone, a potent synthetic glucocorticoid, with estradiol. Treatment of ovariectomized rats with progesterone also lowered the levels of IgA and SC in cervicovaginal secretions. In contrast, dexamethasone had no apparent vaginal effect. The action of estradiol on cervicovaginal IgA, IgG and SC appears to be independent of uterine influence. This conclusion is based upon our observation that estrogen treatment of rats with ligations at their uterocervical junction still have decreased cervicovaginal IgA and SC levels. In parallel with this inhibitory effect, estradiol administration stimulated the accumulation of IgA and SC in uterine secretions. These findings indicate that the sex hormones play a role in regulating IgA, IgG and SC content in cervicovaginal secretions. In addition, it suggests that hormonal balance in females may influence the immune response of the reproductive tract to infectious disease.     

IgA and IgG antibodies to Candida albicans in the genital tract secretions of women with or without vaginal candidosis

Levels of anti-Candida albicans immunoglobulin A (IgA) and IgG were measured by enzyme-linked immunosorbent assay in serum and cervicovaginal secretions from 64 non-pregnant women with vaginal candidosis and 158 uninfected non-pregnant women. Specific IgA and IgG were detected in the serum and secretions of all 222 women. There was no significant difference between the mean levels of specific IgA or IgG in secretions from women with candidosis and those of uninfected women. Neither was there a significant difference between mean levels of specific IgA or IgG when women using oral contraception were compared with others who were not. There was a significant correlation between the levels of IgA and IgG in serum and secretions from women with candidosis and from uninfected women. Blastospore and hyphal forms of C. albicans were seen in vaginal smears from 29 of the 64 women with culture-proven candidosis: in nine, both IgA- and IgG-coated C. albicans cells were recovered from the genital tract; in a tenth, IgG-coated cells were found.     

Mucosal but Not Parenteral Immunization with Purified Human Papillomavirus Type 16 Virus-Like Particles Induces Neutralizing Titers of Antibodies throughout the Estrous Cycle of Mice

We have recently shown that nasal immunization of anesthetized mice with human papillomavirus type 16 (HPV16) virus-like particles (VLPs) is highly effective at inducing both neutralizing immunoglobulin A (IgA) and IgG in genital secretions, while parenteral immunization induced only neutralizing IgG. Our data also demonstrated that both isotypes are similarly neutralizing according to an in vitro pseudotyped neutralization assay. However, it is known that various amounts of IgA and IgG are produced in genital secretions along the estrous cycle. Therefore, we have investigated how this variation influences the amount of HPV16 neutralizing antibodies induced after immunization with VLPs. We have compared parenteral and nasal protocols of vaccination with daily samplings of genital secretions of mice. Enzyme-linked immunosorbent assay analysis showed that total IgA and IgG inversely varied along the estrous cycle, with the largest amounts of IgA in proestrus-estrus and the largest amount of IgG in diestrus. This resulted in HPV16 neutralizing titers of IgG only being achieved during diestrus upon parenteral immunization. In contrast, nasal vaccination induced neutralizing titers of IgA plus IgG throughout the estrous cycle, as confirmed by in vitro pseudotyped neutralization assays. Our data suggest that mucosal immunization might be more efficient than parenteral immunization at inducing continuous protection of the female genital tract.     

Human male genital tract secretions: both mucosal and systemic immune compartments contribute to the humoral immunity

In contrast to numerous studies of female genital tract secretions, the molecular properties of Abs and the magnitude of humoral responses in human male genital tract secretions to naturally occurring Ags and to mucosal and systemic immunizations have not been extensively investigated. Therefore, seminal plasma (SP) collected from healthy individuals was analyzed with respect to Ig levels, their isotypes, molecular forms of IgA, and for the presence of Abs to naturally occurring Ags, or induced by systemic or mucosal immunizations with viral and bacterial vaccines. The results indicated that in SP, IgG and not IgA, is the dominant Ig isotype, and that IgM is present at low levels. IgA is represented by secretory IgA, polymeric IgA, and monomeric IgA. In contrast to the female genital tract secretions in which IgA2 occurs in slight excess, the distribution of IgA subclasses in SP resembles that in plasma with a pronounced preponderance of IgA1. The IgG subclass profiles in SP are also similar to those in serum. Thus, SP is an external secretion that shares common features with both typical external secretions and plasma. Specifically, SP contains naturally occurring secretory IgA Abs to environmental Ags of microbial origin and to an orally administered bacterial vaccine, and plasma-derived IgG Abs to systemically injected vaccines. Therefore, both mucosal and systemic immunization with various types of Ags can induce humoral responses in SP. These findings should be considered in immunization strategies to induce humoral responses against sexually transmitted infections, including HIV-1.     

Induction of anti-chlamydial mucosal immunity by transcutaneous immunization is enhanced by topical application of GM-CSF

Transcutaneous immunization (TCI) involves the direct application of antigen plus adjuvant to skin, taking advantage of the large numbers of Langerhans cells and other resident skin dendritic cells, that process antigen then migrate to draining lymph nodes where immune responses are initiated. We have used this form of immunization to protect mice against genital tract and respiratory tract chlamydial infection. Protection was associated with local antibody responses in the vagina, uterus and lung as well as strong Th1 responses in the lymph nodes draining the reproductive tract and lungs respectively. In this study we show that topical application of GM-CSF to skin enhances the numbers and activation status of epidermal dendritic cells. Topical application of GM-CSF also increased the immune responses elicited by TCI. GM-CSF supplementation greatly increased cytokine (IFNgamma and IL-4) gene expression in lymph node and splenic cells compared to cells from animals immunized without GM-CSF. IgG responses in serum, uterine lavage and bronchoalveolar lavage and IgA responses in vaginal lavage were also increased by topical application of GM-CSF. The studies show that TCI induces protection against genital and respiratory tract chlamydial infections and that topical application of cytokines such as GM-CSF can enhance TCI-induced antibody and cell-mediated immunity.     

Immunohistochemical investigation of secretory component and immunoglobulin A in the genital tract of the female rat

There was intense labelling of secretory component (sc) in the glandular and luminal epithelia of the uterine horns at pro-oestrus, oestrus and Day 1 of pregnancy, but at other stages labelling was weak or undetectable. There was also intense labelling of sc in the superficial layer of cells in the stratified epithelia of the cervix and vagina at pro-oestrus and Days 4-7 of pregnancy, but not at other stages. Plasma cells containing immunoglobulin A (IgA) were not observed in any region of the genital tract at any of the times studied. The presence of sc coupled with an absence of IgA-containing plasma cells suggest that IgA in genital tract secretions of the female rat may be derived mainly from serum.     

Nasal Immunization of Mice with Human Papillomavirus Type 16 (HPV-16) Virus-Like Particles or with the HPV-16 L1 Gene Elicits Specific Cytotoxic T Lymphocytes in Vaginal Draining Lymph Nodes

Human papillomavirus type 16 (HPV-16) infects the genital tract and is closely associated with the development of cervical cancer. HPV-16 initiates infection at the genital mucosal surface; thus, mucosal immune responses are likely to contribute to defense against HPV-16 infection. However, little information is available regarding the induction of immune responses in the genital tract mucosa. In this study, we evaluated the potential of intranasally administered papillomavirus vaccines to elicit both systemic and vaginal immune responses. HPV-16 virus-like particles (VLPs) produced by self-assembly of L1 protein and the HPV-16 L1 gene cloned into a mammalian expression vector were used as vaccines. Intranasally administered VLPs induced serum immunoglobulin G (IgG) and vaginal IgA secretory antibodies. Very weak serum IgG and vaginal IgA responses were found after DNA immunization. Both splenic and vaginal lymphocytes could be activated by intranasal immunization with VLPs and the HPV-16 L1 gene. Activated CD4(+) Th1-like T cells were shown to synthesize gamma interferon, and activated CD8(+) T cells were demonstrated to be cytotoxic.     

Anti-trichomonal IgA antibodies in trichomoniasis before and after treatment

Anti-trichomonal IgA antibodies were estimated by enzyme-linked immunosorbent assay (ELISA) in serum and vaginal secretions of 25 symptomatic and 25 asymptomaticTrichomonas vaginalis positive patients before and after treatment and in 25 age-matched controls. Significantly higher levels of antitrichomonad IgA antibodies were found inT. vaginalis positive patients when compared to control subjects, especially in vaginal secretions. In addition, a significant decrease in these antibodies was observed after treatment, which was more pronounced in vaginal secretions. It seems that anti-trichomonal IgA antibodies in serum and more so in vaginal secretions are directly related to and specific to the presence ofT. vaginalis in the urogenital tract.     

Immunohistochemical localization of immunoglobulins A, G and M in the mouse female genital tract

The localization of immunoglobulins A, G and M (IgA, IgG, IgM) in the mouse genital tract was studied by immunoperoxidase techniques at oestrus, on the day of mating and at the time of implantation. In the horns and body of the uterus, IgA and IgG were located in plasma cells in the endometrium surrounding uterine glands and in the gland lumina. The numbers of these plasma cells increased markedly between Day 1 and Days 4 and 5 of pregnancy and the ratio of plasma cells containing IgA and IgG was about 3 or 4 to 1 at all stages. Area measurements indicated that the increased number of plasmacytes was not due to an increase in the amount of endometrial, myometrial or glandular tissues. Plasma cells were not detected in the cervix and vaginal fornix at oestrus and Day 1, but a few were present on Day 5. In the oviduct, plasma cells containing IgA and IgG were present only in the preampulla and both immunoglobulins were present in the extracellular space of the lamina propria only in this region. No IgM was detected in any part of the reproductive tract at any of the times studied. Uteri on Day 1 of pregnancy contained bacteria of several kinds, some of which were aggregated and coated with IgA. This suggests that the uterine lumen at this time may contain specific anti-bacterial IgA antibodies. Our observations indicate that the horns and body of the uterus and the preampulla of the oviduct are major sites of a local immune system in the female mouse genital tract.     

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.     

Mucosal model of genital immunization in male rhesus macaques with a recombinant simian immunodeficiency virus p27 antigen.

Human immunodeficiency virus (HIV) can be transmitted through infected seminal fluid or vaginal or rectal secretions during heterosexual or homosexual intercourse. To prevent mucosal transmission and spread to the regional lymph nodes, an effective vaccine may need to stimulate immune responses at the genitourinary mucosa. In this study, we have developed a mucosal model of genital immunization in male rhesus macaques, by topical urethral immunization with recombinant simian immunodeficiency virus p27gag, expressed as a hybrid Ty virus-like particle (Ty-VLP) and covalently linked to cholera toxin B subunit. This treatment was augmented by oral immunization with the same vaccine but with added killed cholera vibrios. Polymeric secretory immunoglobulin A (sIgA) and IgG antibodies to p27 were induced in urethral secretions, urine, and seminal fluid. This raises the possibility that the antibodies may function as a primary mucosal defense barrier against SIV (HIV) infection. The regional lymph nodes which constitute the genital-associated lymphoid tissue contained p27-specific CD4+ proliferative and helper T cells for antibody synthesis by B cells, which may function as a secondary immune barrier to infection. Blood and splenic lymphocytes also showed p27-sensitized CD4+ T cells and B cells in addition to serum IgG and IgA p27-specific antibodies; this constitutes a third level of immunity against dissemination of the virus. A comparison of genito-oral with recto-oral and intramuscular routes of immunization suggests that only genito-oral immunization elicits specific sIgA and IgG antibodies in the urine, urethra, and seminal fluid. Both genito-oral and recto-oral immunizations induced T-cell and B-cell immune responses in regional lymph nodes, with preferential IgA antibody synthesis. The mucosal route of immunization may prevent not only virus transmission through the genital mucosa but also dissemination and latency of the virus in the draining lymph nodes.     

Immunoglobulin G, Plasma Cells, and Lymphocytes in the Murine Vagina after Vaginal or Parenteral Immunization with Attenuated Herpes Simplex Virus Type 2

This investigation evaluated immunity to vaginal herpes simplex virus type 2 (HSV-2) infection after local or parenteral immunization with attenuated HSV-2. Vaginal immunization induced sterilizing immunity against challenge with a high dose of wild-type virus, whereas parenteral immunizations protected against neurologic disease but did not entirely prevent infection of the vagina. Vaginal immunization caused 86- and 31-fold increases in the numbers of immunoglobulin G (IgG) plasma cells in the vagina at 6 weeks and 10 months after immunization, whereas parenteral immunizations did not increase plasma cell numbers in the vagina. Vaginal secretion/serum titer ratios and specific antibody activities in vaginal secretions and serum indicated that IgG viral antibody was produced in the vagina and released into vaginal secretions at 6 weeks and 10 months after vaginal immunization but not after parenteral immunizations. In contrast to the case for plasma cells, the numbers of T and B lymphocytes in the vagina were similar in vaginally and parenterally immunized mice. Also, lymphocyte numbers in the vagina were markedly but similarly increased by vaginal challenge with HSV-2 in both vaginally and parenterally immunized mice. Lymphocyte recruitment to the vagina after virus challenge appeared to involve memory lymphocytes, because it was not observed in nonimmunized mice. Thus, local vaginal immunization with attenuated HSV-2 increased the number of IgG plasma cells in the vagina and increased vaginal secretion/serum titer ratios to 3.0- to 4.7-fold higher than in parenterally immunized groups but caused little if any selective homing of T and B lymphocytes to the vagina.     

Combined oral/nasal immunization protects mice from Sendai virus infection

Based on the concept of a common mucosal immune system wherein mucosal associated lymphocytes traffic among the various mucous membranes, the murine gastrointestinal tract was immunized with Sendai virus antigens in order to elicit a virus-specific immune response in the respiratory tract. Multiple intragastric (oral) administration of live or killed Sendai virus induced IgA and IgG antiviral antibodies in both gastrointestinal secretions and serum. When cholera toxin as an adjuvant was included along with virus, gut IgA and IgG as well as serum IgA responses were enhanced. Antiviral antibodies induced in respiratory secretions by oral killed virus plus cholera toxin, however, were variable and protection from virus challenge was not demonstrated. Significantly higher levels of respiratory antiviral antibodies were induced if immunization with oral killed Sendai virus/cholera toxin was combined with intranasal administration of small amounts of killed virus. The combined immunization also resulted in protection of both the upper and lower respiratory tracts from virus infection. Protection of the upper respiratory tract was correlated with the presence of IgA antiviral antibodies in nasal washings. On the other hand, protection of the lower respiratory tract was correlated with IgG antiviral antibodies in bronchoalveolar lavage fluids. Immunization with intranasal killed virus alone conferred partial protection to the lower respiratory tract and no protection to the upper respiratory tract. Thus, oral immunization with killed virus antigen could prime for a protective immune response in the murine respiratory tract and this protective response included IgA antibodies.     

Alternate mucosal immune system: organized Peyer's patches are not required for IgA responses in the gastrointestinal tract

The progeny of mice treated with lymphotoxin (LT)-beta receptor (LTbetaR) and Ig (LTbetaR-Ig) lack Peyer's patches but not mesenteric lymph nodes (MLN). In this study, we used this approach to determine the importance of Peyer's patches for induction of mucosal IgA Ab responses in the murine gastrointestinal tract. Immunohistochemical analysis revealed that LTbetaR-Ig-treated, Peyer's patch null (PP null) mice possessed significant numbers of IgA-positive (IgA+) plasma cells in the intestinal lamina propria. Further, oral immunization of PP null mice with OVA plus cholera toxin as mucosal adjuvant resulted in Ag-specific mucosal IgA and serum IgG Ab responses. OVA-specific CD4+ T cells of the Th2 type were induced in MLN and spleen of PP null mice. In contrast, when TNF and LT-alpha double knockout (TNF/LT-alpha-/-) mice, which lack both Peyer's patches and MLN, were orally immunized with OVA plus cholera toxin, neither mucosal IgA nor serum IgG anti-OVA Abs were induced. On the other hand, LTbetaR-Ig- and TNF receptor 55-Ig-treated normal adult mice elicited OVA- and cholera toxin B subunit-specific mucosal IgA responses, indicating that both LT-alphabeta and TNF/LT-alpha pathways do not contribute for class switching for IgA Ab responses. These results show that the MLN plays a more important role than had been appreciated until now for the induction of both mucosal and systemic Ab responses after oral immunization. Further, organized Peyer's patches are not a strict requirement for induction of mucosal IgA Ab responses in the gastrointestinal tract.