As lower respiratory infections are a leading cause of morbidity and mortality worldwide, and have been linked to periodic pandemics, there is a heightened interest in understanding how protective immune cells are mobilized in response to pathogens and contribute to local tissue resistance. The existence of non-recirculating lung resident memory B (BRM) cells was recently defined in an influenza virus infection model and inferred to be protective. Our body of knowledge has since grown significantly, but many unknowns including BRM cell establishment dynamics and requirements for maintenance remain. We previously used a murine model of serotype-independent immunity against Streptococcus pneumoniae (Sp) to show that resident memory B (BRM) cells are seeded extravascularly in the lung after local bacterial exposures independently of mature tertiary lymphoid structure formation. Using a transgenic mouse model which allowed for the depletion of PD-L2+ memory B cells, we demonstrated that lung PD-L2+ BRM cells directly contribute to clearance of a heterotypic Sp challenge infection, and that their absence correlated with diminished local antibody secreting cell (ASC) activities. Our findings provide evidence of serotype-independent protection mediated by the PD-L2+ BRM cell population and suggest that this is due to their capacity to rapidly differentiate into local ASCs upon memory recall. We carried out additional studies to elucidate lung B cell population dynamics, locations, and T-dependent requirements for establishment and maintenance after Sp infections. Singular exposure to self-limiting pneumococcal infection was insufficient to generate lasting BRM cells, as well as other heterogeneous extravascular B cell populations which were tracked over time. This included a transient population of proliferatively active lung GC B cells whose accumulation in the lung corresponded with the temporary appearance of organized lymphoid tissue. After an initial respiratory infection was administered to allow for immune priming in the lung and in draining lymph nodes, disruption of T cell interactions during a 2nd infection prevented pan extravascular B cell accumulation and abrogated lung BRM cells. We posit that our findings are relevant for the development of improved serotype-independent preventative strategies against pneumococcal pneumonia, and all respiratory pathogens in general. Advancing our understanding of tissue-resident B cell populations will aid in the development of next generation vaccines that leverage mucosal memory against respiratory pathogens. / 2025-02-12T00:00:00Z

One of the fundamental questions in mucosal immunology is how the intestine maintains tolerance to food antigens and commensal flora, and yet it is capable of mounting immune responses to pathogens. Peyers patches (PP) are lymphoid aggregates that are found in the small intestine and are the primary sites where adaptive immune responses are initiated in the intestine. An understanding of how PP cells regulate innate immune responses may provide information on how immune responses are regulated in the intestine. The toll-like receptors (TLRs) are a family of pattern recognition receptors (PRR) which provide a sensory mechanism for the detection of infectious threats. TLR9 recognizes bacterial DNA or synthetic CpG oligodeoxynucleotides (ODN). Cells that express TLR9 when stimulated with CpG ODN proliferate and produce Th1-like pro-inflammatory cytokines and upregulate co-stimulatory molecules. Because the intestine is constantly exposed to bacterial DNA from commensal flora, immune cells from the gut must have evolved mechanisms to modulate responses to TLR9 stimulation to prevent responses to harmless bacteria. Our hypothesis is that innate immune responses to the TLR9 agonist CpG ODN in Peyers patches (PP) are attenuated compared to other tissues such as blood or lymph nodes. This is due to local regulatory mechanisms unique to the intestinal microenvironment.<p> We conducted a number of experiments to test this hypothesis. We initially assessed the immunostimulatory activity of three available classes of CpG ODN in lymph nodes (LN), peripheral blood mononuclear cells (PBMC) and PP since this had not been done in ruminants. We found that CpG ODN induced strong IFNá, IFN-gamma, IL-12, lymphocyte proliferation and NK-like activity in LN and PBMC. In contrast, these responses were significantly less in PP stimulated with CpG ODN. We wondered whether the reduced responses of PP cells to CpG ODN were unique to the TLR9 agonist. For this reason we tested responses of cells from these tissues to poly (I:C), LPS, and single-stranded RNA, which are agonists for TLR3, TLR4, and TLR7/8 respectively. Additionally, we tested combinations of TLRs since others have reported that multiple TLR agonists may induce synergistic responses. All TLR agonists or their combinations either failed to induce detectable responses or the responses were significantly less in PP compared to other tissues. Thus we concluded that PP cells responses to TLR stimulation were attenuated. In all tissues tested, there were no synergistic responses (IFN-alpha, IFN-gamma and lymphocyte proliferation) following stimulation with combinations of agonists. However, there was inhibition of PBMC responses when TLR7/8 agonists were combined with CpG ODN (TLR9 agonist). Importantly, TLR7/8 agonists reduced the CpG-induced proliferative responses in purified blood B cells. Interestingly, ovine B cells constitutively expressed TLR7/8 and TLR9 mRNA, suggesting the potential for cross-talk between the receptors.<p> Interestingly, cell from all isolated tissues [ileal PP (IPP), jejunal PP (JPP), mesenteric LN (mLN) and PBMC] expressed similar levels of TLR9 mRNA, suggesting that the reduced responsiveness to CpG ODN stimulation in PP was not due to a lack of TLR9 expression.<p> Surprisingly, we observed that PP cells spontaneously secreted significant amounts of the immunoregulatory cytokine IL-10. Furthermore, we confirmed that CD21+ B cells were the source of the IL-10. We then examined the role of IL-10 in regulating IFN and IL-12 responses in PP. Neutralization of IL-10 resulted in a significant increase in the numbers of CpG-induced IFNá-secreting cells detected and in IFN-gamma and IL-12 production by PP cells (both follicular and interfollicular lymphocytes). Similarly, depletion of the CD21+ B cells resulted in significant increases in IFNá, IFN-gamma and IL-12 responses. These observations support the conclusion that IL-10-secreting PP CD21+ B cells suppress innate immune responses in PP. Further characterization by flow cytometry revealed that these cells were CD1b-CD5-CD11c-CD72+CD21+ IgM+ B cells. We have proposed that these IL-10-secreting PP CD21+ B cells are a novel subset of regulatory B cells (Bregs).<p> Finally, we examined the capacity of IL-10 secreting B cells (Bregs) to respond to CpG ODN. To achieve this, we compared CD21+ B cells from blood and JPP. Unlike blood CD21+ B cells, CD21+ B cells from JPP proliferated poorly in response to CpG ODN. Moreover, PP CD21+ B cells, unlike blood CD21+ B cells, do not secrete IgM or IL-12 in response to CpG stimulation, although both PP and blood CD21+ B cells express similar level of TLR9 mRNA. Neutralization of IL-10 did not enhance CpG-induced proliferative responses in PP CD21+ B cells. Thus IL-10 does not play a direct role in the hyporesponsiveness of PP CD21+ B cells to CpG ODN. To further explore the mechanism by which PP Bregs fail to respond to CpG ODN stimulation, we used a kinome analysis to determine whether the TLR9 pathway was functional in PP Bregs compared to blood CD21+ B cells. We observed that peptides representing critical adaptor molecules downstream of TLR9 such as IRAK1, TAK1, Casp8, p-38 MAPK, JNK, FOS, IKKá, NF-KB-p65 were not phosphorylated in JPP CD21+ B cells following CpG ODN stimulation. However, in blood CD21+ B cells stimulated with CpG ODN, the same peptides on the array were all highly phosphorylated leading to a functional TLR9 signaling pathway. Thus PP Bregs have evolved mechanisms by which the TLR9 signaling pathway is not activated following exposure to the TLR9 agonist, CpG ODN.<p> In conclusion, we clearly demonstrated that TLR9-induced responses in cells from PP are significantly attenuated. This is a consequence of PP CD21+ B cells (Bregs) that spontaneously secrete IL-10, which in turn conditions an anti-inflammatory environment in this tissue leading to poor cytokine responses to the TLR9 agonist, CpG ODN. Additionally, we show that Bregs are unresponsiveness to TLR9 stimulation. This unresponsiveness is due to regulatory mechanisms in Bregs leading to a dysfunctional TLR9 signaling pathway. These may represent strategies by which PP dampen innate responses to pathogen-associated molecular patterns (PAMPs) in intestinal immune tissues to maintain intestinal immune homeostasis. These conclusions are consistent with our hypothesis that TLR responses in PP cells are attenuated, and this is due to B cell-mediated regulatory mechanisms that are unique to the intestinal microenvironment.

One of the fundamental questions in mucosal immunology is how the intestine maintains tolerance to food antigens and commensal flora, and yet it is capable of mounting immune responses to pathogens. Peyers patches (PP) are lymphoid aggregates that are found in the small intestine and are the primary sites where adaptive immune responses are initiated in the intestine. An understanding of how PP cells regulate innate immune responses may provide information on how immune responses are regulated in the intestine. The toll-like receptors (TLRs) are a family of pattern recognition receptors (PRR) which provide a sensory mechanism for the detection of infectious threats. TLR9 recognizes bacterial DNA or synthetic CpG oligodeoxynucleotides (ODN). Cells that express TLR9 when stimulated with CpG ODN proliferate and produce Th1-like pro-inflammatory cytokines and upregulate co-stimulatory molecules. Because the intestine is constantly exposed to bacterial DNA from commensal flora, immune cells from the gut must have evolved mechanisms to modulate responses to TLR9 stimulation to prevent responses to harmless bacteria. Our hypothesis is that innate immune responses to the TLR9 agonist CpG ODN in Peyers patches (PP) are attenuated compared to other tissues such as blood or lymph nodes. This is due to local regulatory mechanisms unique to the intestinal microenvironment.<p> We conducted a number of experiments to test this hypothesis. We initially assessed the immunostimulatory activity of three available classes of CpG ODN in lymph nodes (LN), peripheral blood mononuclear cells (PBMC) and PP since this had not been done in ruminants. We found that CpG ODN induced strong IFNá, IFN-gamma, IL-12, lymphocyte proliferation and NK-like activity in LN and PBMC. In contrast, these responses were significantly less in PP stimulated with CpG ODN. We wondered whether the reduced responses of PP cells to CpG ODN were unique to the TLR9 agonist. For this reason we tested responses of cells from these tissues to poly (I:C), LPS, and single-stranded RNA, which are agonists for TLR3, TLR4, and TLR7/8 respectively. Additionally, we tested combinations of TLRs since others have reported that multiple TLR agonists may induce synergistic responses. All TLR agonists or their combinations either failed to induce detectable responses or the responses were significantly less in PP compared to other tissues. Thus we concluded that PP cells responses to TLR stimulation were attenuated. In all tissues tested, there were no synergistic responses (IFN-alpha, IFN-gamma and lymphocyte proliferation) following stimulation with combinations of agonists. However, there was inhibition of PBMC responses when TLR7/8 agonists were combined with CpG ODN (TLR9 agonist). Importantly, TLR7/8 agonists reduced the CpG-induced proliferative responses in purified blood B cells. Interestingly, ovine B cells constitutively expressed TLR7/8 and TLR9 mRNA, suggesting the potential for cross-talk between the receptors.<p> Interestingly, cell from all isolated tissues [ileal PP (IPP), jejunal PP (JPP), mesenteric LN (mLN) and PBMC] expressed similar levels of TLR9 mRNA, suggesting that the reduced responsiveness to CpG ODN stimulation in PP was not due to a lack of TLR9 expression.<p> Surprisingly, we observed that PP cells spontaneously secreted significant amounts of the immunoregulatory cytokine IL-10. Furthermore, we confirmed that CD21+ B cells were the source of the IL-10. We then examined the role of IL-10 in regulating IFN and IL-12 responses in PP. Neutralization of IL-10 resulted in a significant increase in the numbers of CpG-induced IFNá-secreting cells detected and in IFN-gamma and IL-12 production by PP cells (both follicular and interfollicular lymphocytes). Similarly, depletion of the CD21+ B cells resulted in significant increases in IFNá, IFN-gamma and IL-12 responses. These observations support the conclusion that IL-10-secreting PP CD21+ B cells suppress innate immune responses in PP. Further characterization by flow cytometry revealed that these cells were CD1b-CD5-CD11c-CD72+CD21+ IgM+ B cells. We have proposed that these IL-10-secreting PP CD21+ B cells are a novel subset of regulatory B cells (Bregs).<p> Finally, we examined the capacity of IL-10 secreting B cells (Bregs) to respond to CpG ODN. To achieve this, we compared CD21+ B cells from blood and JPP. Unlike blood CD21+ B cells, CD21+ B cells from JPP proliferated poorly in response to CpG ODN. Moreover, PP CD21+ B cells, unlike blood CD21+ B cells, do not secrete IgM or IL-12 in response to CpG stimulation, although both PP and blood CD21+ B cells express similar level of TLR9 mRNA. Neutralization of IL-10 did not enhance CpG-induced proliferative responses in PP CD21+ B cells. Thus IL-10 does not play a direct role in the hyporesponsiveness of PP CD21+ B cells to CpG ODN. To further explore the mechanism by which PP Bregs fail to respond to CpG ODN stimulation, we used a kinome analysis to determine whether the TLR9 pathway was functional in PP Bregs compared to blood CD21+ B cells. We observed that peptides representing critical adaptor molecules downstream of TLR9 such as IRAK1, TAK1, Casp8, p-38 MAPK, JNK, FOS, IKKá, NF-KB-p65 were not phosphorylated in JPP CD21+ B cells following CpG ODN stimulation. However, in blood CD21+ B cells stimulated with CpG ODN, the same peptides on the array were all highly phosphorylated leading to a functional TLR9 signaling pathway. Thus PP Bregs have evolved mechanisms by which the TLR9 signaling pathway is not activated following exposure to the TLR9 agonist, CpG ODN.<p> In conclusion, we clearly demonstrated that TLR9-induced responses in cells from PP are significantly attenuated. This is a consequence of PP CD21+ B cells (Bregs) that spontaneously secrete IL-10, which in turn conditions an anti-inflammatory environment in this tissue leading to poor cytokine responses to the TLR9 agonist, CpG ODN. Additionally, we show that Bregs are unresponsiveness to TLR9 stimulation. This unresponsiveness is due to regulatory mechanisms in Bregs leading to a dysfunctional TLR9 signaling pathway. These may represent strategies by which PP dampen innate responses to pathogen-associated molecular patterns (PAMPs) in intestinal immune tissues to maintain intestinal immune homeostasis. These conclusions are consistent with our hypothesis that TLR responses in PP cells are attenuated, and this is due to B cell-mediated regulatory mechanisms that are unique to the intestinal microenvironment.

Heterosexual intercourse now accounts for the majority of HIV transmission within sub-Saharan Africa. The generation of microbicides and vaccines, therefore, requires a better understanding of the mucosal correlates of protection, including the role of HIV-specific IgA. It is now accepted that not all individuals are equally susceptible to HIV-1 infection, as exemplified by the HIV Exposed Seronegative (HESN) women of the Pumwani Cohort in Nairobi, Kenya. To assess whether mucosal IgA responses contribute to this protection, 3 novel IgA variable genes were cloned from HESN cervical B-cell cDNA. Nine monoclonal IgA Abs were produced, two of which were properly produced from cell culture. The HESN-derived A6/30L and A9/30L variants had a greater specificity for gp120IIIB than their A6/4L and A9/4L counterparts, while the A6 variant recognizes a distinct gp120 epitope compared to the broadly neutralizing antibody IgGb12. Further characterization of these IgA chains may suggest their suitability for use in microbicides or mucosal vaccines.

Heterosexual intercourse now accounts for the majority of HIV transmission within sub-Saharan Africa. The generation of microbicides and vaccines, therefore, requires a better understanding of the mucosal correlates of protection, including the role of HIV-specific IgA. It is now accepted that not all individuals are equally susceptible to HIV-1 infection, as exemplified by the HIV Exposed Seronegative (HESN) women of the Pumwani Cohort in Nairobi, Kenya. To assess whether mucosal IgA responses contribute to this protection, 3 novel IgA variable genes were cloned from HESN cervical B-cell cDNA. Nine monoclonal IgA Abs were produced, two of which were properly produced from cell culture. The HESN-derived A6/30L and A9/30L variants had a greater specificity for gp120IIIB than their A6/4L and A9/4L counterparts, while the A6 variant recognizes a distinct gp120 epitope compared to the broadly neutralizing antibody IgGb12. Further characterization of these IgA chains may suggest their suitability for use in microbicides or mucosal vaccines.

The gastrointestinal mucosal immune system has the daunting task of maintaining immune homeostasis by eliminating potentially harmful microorganisms and limiting tissue injury while inducing tolerogenic responses to luminal antigens including innocuous food, commensal bacteria and self-antigens. This carefully orchestrated system depends on elaborate down-regulating mechanisms that mediate and maintain a state of tolerance under normal conditions. Changes in such delicate balance are linked to the development of gastrointestinal pathology as well as systemic disease states. Despite the rapid increase in our appreciation of the gastrointestinal immune system, there is still a major disconnect between the description of how mucosal immune responses are organized and controlled and an insufficient mechanistic understanding of how such responses shape and influence disease outcome and pathogenesis. By using model enteric microorganisms Helicobacter pylori and Clostridium difficile, this dissertation presents a systematic effort to generate novel mechanistic hypothesis based on computational predictions and experimentally elucidate the mechanisms of action underlying mucosal immune responses and pathology in the gut. In this thesis I present i) an overview on mucosal immunology and the need to develop novel therapeutics that limit the pathogenic effects of invading bacteria while maintaining their protective functions, ii) the role of miRNAs in the modulation of immune responses to enteric pathogens, iii) the mechanisms by which Helicobacter pylori is able to limit effector inflammatory responses required for bacterial clearance thus favoring tolerance over immunity, iv) intracellular mechanisms of immune evasion that contribute to bacterial persistence and chronic infection. The knowledge generated throughout this dissertation exemplifies how a combination of computational modeling, immunoinformatics and experimental immunology holds enormous potential for discovering unforeseen targets and developing novel vaccines and cures for infectious, allergic and immune-mediated diseases. / Ph. D.

Intestinal homeostasis is a delicate balance between suppression of immune responses against innocuous antigens and stimulation of immune responses against pathogens. Type I interferon (IFN-1) cytokines have both immunostimulatory and immunomodulatory effects. Colon mononuclear phagocytes (MP) constitutively produced IFN-1 in a TRIFdependent manner. We explored the function of endogenous IFN-1 in the colon using the T cell adoptive transfer model of colitis. Transfer of CD4⁺CD45RB^hi naïve T cells from wild type (WT) or IFNAR subunit 1 knockout (IFNAR1^-/-) mice into RAG^-/- hosts resulted in similar onset and severity of colitis. In contrast, RAG^-/- x IFNAR1^-/- double knockout (DKO) mice developed accelerated severe colitis compared to RAG^-/- hosts when transferred WT CD4⁺CD45RB^hi T cells. Although WT or IFNAR1^-/- regulatory T (Treg) cells equally prevented disease caused by CD45RB^hi naïve T cells, WT Treg cells co-transferred with naïve CD4⁺ T cells into DKO recipients failed to expand or maintain Foxp3 expression and gained effector functions in the colon. IFNAR signaling on host hematopoietic cells inhibited T cell-mediated colitis, but not innate colitis. MPs isolated from the colon lamina propria (cLP) required IFNAR signaling for the production of the anti-inflammatory cytokines, IL-10, IL-27, and IL-1RA, but not for the production of classic pro-inflammatory cytokines. IFN-1-dependent secretion of IL-1RA was particularly important in inhibiting the migration of inflammatory DCs with potent T cell proliferative capacity from the cLP to the mesenteric lymph nodes. Finally, preliminary results suggested that IFN-1 may shape the commensal microbiota, but is not essential for controlling specific colitis-inducing bacteria.

Mucosal associated invariant T-cells (MAIT) are a phylogenetically conserved subset of alpha/beta T-cells with natural killer-like (NK) activity. MAIT are defined by the expression of an invariant T-cell receptor alpha (TCRα) chain; in mice and humans this chain uses the orthologous mVα19/hVα7.2-Jα33 genes respectively. Available evidence indicates that MAIT are restricted by MR1, a highly conserved MHC class I-related molecule, and that their development is dependent on B lymphocytes. They appear to constitute part of the innate immune response, but their precise functional role is poorly understood. This study aimed to characterise MAIT and MR1 in ruminants, and to further the knowledge and understanding of these unique cells. Using PCR primers based on partial database sequences, orthologous full-length TCRα chains were identified in circulating bovine and ovine T cells. The germline elements of the respective α chains were identified and their overall frequency of expression within the bovine TCRα repertoire determined. Experiments using the orthologous TCRα chain as a marker for MAIT cells to examine expression in bovine and ovine blood and various tissues showed that spleen and mesenteric lymph nodes contained the highest frequency of MAIT cells. Use of the same technique to study levels of this marker in cattle of different ages revealed very low numbers of MAIT cells in neonatal animals, followed by a marked increase in the first 3 weeks of life. Analyses of MAIT TCRα expression in different T cell subsets showed that, unlike mice and humans in which MAIT cells are predominantly within the CD4-/CD8- T-cell population, MAIT cells in bovine blood are predominantly CD8+. Full-length cDNAs were isolated for bovine and sheep MR1 and their sequences were found to display marked cross-species conservation. Using a specific PCR, MR1 was shown to be expressed in peripheral blood and by different lineages of Theileria-transformed cells. Alternatively-spliced transcripts of MR1 were detected in both cattle and sheep and several of these retained an intact open-reading frame. Constructs of bovine MR1 and an MR1/MHC chimera were prepared in a eukaryotic expression vector but these failed to give detectable cell surface expression following transfection into Cos-7, despite positive intracellular expression.

In the age of highly active antiretroviral therapy (HAART), patients infected with Human Immunodeficiency Virus Type 1 (HIV-1) are now living significantly healthier and longer lives. However, HIV prevention and cure still remain significant challenges. Globally, women face specific barriers to using and accessing both female and male condoms, the primary method recommended by the World Health Organization (WHO) to prevent sexual transmission of HIV-1. Although HAART treatment as prevention (TasP) of HIV has shown promising preliminary results, poor economic feasibility of the method in resource poor settings has yet to be resolved. Since women carry over 50% of the disease burden, there is a significant need for the development of a female-controlled method of prevention. One such approach is the reformulation of topical vaginal microbicides. Our laboratory is developing HIV-targeted microbicide formulations that utilize highly specific, broadly neutralizing anti-HIV antibodies (bNAbs). The purpose of my research project was to characterize Fc receptor expression in epithelial cell models of the lower female genital tract with a particular focus on the neonatal Fc receptor (FcRn). Fc receptors are a large family of proteins that bind to the Fc region of immunoglobulins (Igs) and function in Ig transport and effector functions. These receptors could function in enhancing the delivery of bNAbs in microbicide formulations or potentially serve as a mechanism of delivering HIV to target cells in tissues via transport of HIV-antibody complexes. Thus, this thesis assesses Fc receptor expression in human vaginal and endocervical organotypic cultures via microarray, quantitative RT-PCR, immunohistology and preliminary functional assays. Microarray results revealed significant expression of Fc receptor family genes in the epithelial cells of the lower female reproductive tract (FRT). The polymeric immunoglobulin receptor (pIgR), a well-characterized receptor that transports secretory IgA across mucosal epithelia, was abundantly expressed and hormonally regulated in epithelial cells of the vagina and endocervix. FcRn, a receptor originally characterized in the placenta and gut where it confers passive immunity from mother-to-child via bidirectional IgG transcytosis, was expressed in both tissue models. Moreover, several members of the novel FC receptor-like (FCRL) family were detected by microarray in both models. Immunohistological staining revealed pIgR protein in the endocervical mucosal epithelium, confirming current literature describing its expression in the FRT and role in local production of cervicovaginal secretions. FcRn protein expression was detected in the basal cell layer of the stratified squamous vaginal epithelium and in the columnar cells of the endocervix. Preliminary functional assays did not observe FcRn-specific transcytosis of human IgG across vaginal or endocervical epithelia by ELISA or immunohistology. VRCO1, a monoclonal antibody in development for application in microbicide formulation, crossed the epithelium, but was likely not transcytosed via FcRn because immunohistology revealed the presence of antibody between epithelial cells rather than the expected intracellular localization of IgG utilized in the FcRn mechanism. These preliminary findings indicate that Fc receptors, pIgR and Fc receptor-like proteins may play an important role in antibody-mediated immune responses in the FRT. Further research is require to determine whether FcRn functions in HIV-antibody complex-mediated HIV transmission or monoclonal antibody transcytosis.

O objetivo desta pesquisa foi avaliar a influência do envelhecimento e da perda dos elementos dentais nos níveis totais de imunoglobulina secretória do tipo A (SIgA) na saliva. Foram selecionados 76 pacientes (entre 20 e 87 anos), os quais foram divididos em três grupos de acordo com sua faixa etária e condição bucal: adultos jovens com idades de 20 a 40 anos (Grupo I ou Grupo controle); idosos com idade entre 65 e 78 anos, desdentados parciais, portadores de prótese total unimaxilar (Grupo II) e idosos com idade entre 65 e 87 anos, desdentados totais, portadores de prótese total bimaxilar (Grupo III). Os níveis totais de imunoglobulina secretória do tipo A na saliva foram determinados por meio da técnica de ensaio imunoenzimático em fase sólida ( ELISA – Enzyme-linked Imunosorbent Assay). Após obtenção dos dados experimentais foi empregada a análise de variância de ANOVA com dois fatores (sexo e grupo) para verificar o efeito significante da interação destes fatores. Os níveis totais de imunoglobulina do tipo A secretória na saliva não apresentaram, em média, diferenças significantes entre os três grupos. Em relação ao fator gênero, ou sexo, em média, homens e mulheres apresentaram comportamentos de SIgA diferentes nos grupos. Para o grupo controle o nível total de SIgA dos homens foi maior que o das mulheres enquanto que para o grupo III o nível total de SIgA das mulheres foi maior que dos homens e para o grupo II não foi observada diferença significante dos níveis de SIgA entre homens e mulheres. Pela análise comparativa dos grupos I e III foi observada diferença significante no sexo feminino, o que não foi observado quando comparados os dois grupos experimentais (Grupos II e III). Os resultados desta pesquisa sugerem que não há influência direta dos fatores envelhecimento e perda dental sobre os níveis totais de imunoglobulina secretória do tipo A na saliva. Estes resultados mostraram a influência do gênero sobre os níveis de imunoglobulina secretória do tipo A. Entretanto, a influência do gênero não é bem conhecida e merece mais estudos. / The aim of this study was to evaluate the influence of senescence and teeth loss on secretory immunoglobulin A (SIgA) levels in saliva. Seventy-six patients (20 to 87 years old) were selected and classified in three groups according to their age and oral dental state: young adults were aged 20-40 years (Group I or Control group); elderly subjects were aged 65-78 years and wore maxillary or mandibular denture (Group II); and edentulous old subjects were aged 65-87 years and wore maxillary and mandibular denture (Group III). The secretory immunoglobulin A levels were determined by the Enzyme-linked imunosorbent assay (ELISA method). All results were correlated using ANOVA statistical analysis with two factors (sex and group) to verify the significant effect of these factors. The secretory immunoglobulin A levels were not significant differences among the average values of the three groups. In gender relation , men and women showed the mean rate of SIgA levels different in the groups. The men SIgA levels of control group showed greater when compared to women levels. In Group III the women levels were greater when compared to men levels. And to Group II statistical analysis demonstrated no significant difference between the SIgA levels of men and women. The analysis showed significant differences in the women levels when compared to Groups I and III. No differences of levels were demonstrated when compared to Groups II and III. These results suggests that the senescence and teeth loss do not have a direct relationship to the secretory immunoglobulin A levels in whole saliva. The se results showed that there is influence of gender in the secretory immunoglobulin levels. However, the influence of gender is not well known and further studies are still necessary.