Toll-like receptors (TLRs) recognize microbial components as danger signals and induce immune responses. TLR’s are expressed in many tissues of the host that are involved in immune responses including the intestines where they are abundantly expressed. This situation presents a challenge in the gastrointestinal tract which is constantly exposed to a wide variety of commensal organisms. Therefore, innate immune recognition in the intestine must be tightly regulated to prevent unwanted inflammation against harmless commensal micro-organisms and yet allow for the induction of protective immunity to invading pathogens. A dysregulation of this balance can result in intestinal inflammation. Peyer’s patches (PP) are the primary site for the induction of immune responses in the intestine and abundantly express TLRs. It is not known how PP regulate microbial signals from commensal bacteria and yet mount vigorous immune responses against dangerous pathogens. CpG DNA, an agonist for TLR9, can strongly activate immune cells in blood, lymph nodes and spleen. However, CpG very poorly activates immune cells from Peyer’s patches, although these cells express TLR9 [1, 2]. Understanding how TLR responses are regulated in PP cells will unveil important information on how immune responses are regulated in the intestine. Investigations from our laboratory have revealed a B cell population (CD5-CD11c-CD21+) in PP that spontaneously secrete high levels of IL-10 which in turn down regulates TLR9 induced IFN and IL-12 production. These IL-10-secreting PP B cells represent a novel subset of the recently proposed regulatory B cells (Bregs) in the intestine [1, 3]. Bregs may have a role in maintaining tolerance to commensal bacteria thereby achieving intestinal homeostasis. The overall goal of the work described in this thesis was to improve our understanding of the immunobiology of Bregs. We performed several experiments to achieve this goal. First, we studied the development of regulatory B cells in lambs of different ages. Jejunal PP were collected from 3-4 month old, neonatal and fetal lambs and the production of IL-10 (the immunoregulatory cytokine secreted by Bregs) was assayed. We found that IL-10 was secreted by CD21+ B cells from the PP in all the three age groups, confirming that Bregs develop prior to birth. We then wondered whether our CD21+ B cells might be contaminated with other cells or activated when using MACS to enrich B cells. To address this issue, we prepared very highly purified CD21+ B cell population using high speed cell sorting to negatively enrich for B cells. We also sorted DCs and assayed IL-10 production in both cell populations. Only the PP B cells spontaneously secreted IL-10. In contrast, dendritic cells, T cells, macrophages, neutrophils and NK cells did not secrete detectable IL-10. Since B cells exist as regulatory and effector populations in mice, we wondered whether an effector B cell population also existed in ovine PP that secreted the pro-inflammatory cytokines IFN-, IFN- and IL-12. Therefore, ovine PP B cells were fractionated into CD72+CD21+and CD72+CD21- subpopulations to assess their capacity to secrete pro-inflammatory cytokines. Interestingly, the CD72+CD21- B cell population secreted the cytokines IFN-, IFN- and IL-12 suggesting there was an effector population. We then surveyed for Bregs in different mucosal and peripheral tissues in sheep. We observed the Bregs frequency varied among the different lymphoid tissues. Finally, we investigated whether Bregs were present in PP of other ruminant species. We identified Bregs exist in PP of neonatal calves. In conclusion, our investigations reveal that ovine Bregs develop in utero prior to antigen exposure, and are present in a variety of mucosal and peripheral tissues. We also report the novel observation that two distinct B cell sub-populations are present in ovine jejunal PP’s: Regulatory and effector B cells.

Understanding natural mechanisms of protection against HIV infection and disease progression are key priorities for informing vaccine and microbicide design. The research presented in this thesis aimed to characterize mechanisms of defence in HIV-exposed seronegative (HESN) individuals, who naturally resist infection by HIV, and HIV-controllers, who are HIV-infected, but suppress viral replication in the absence of treatment. Previous studies have linked resistance to HIV infection with low basal levels of gene transcription and reduced production of inflammatory mediators, suggesting an overall state of immune quiescence in HESN. Immune quiescence may also be protective in HIV-infected individuals, as immune activation drives disease progression. The central hypothesis of this thesis is that immune quiescence protects against HIV infection and disease progression by limiting the pool of activated target CD4+ T cells susceptible to HIV infection. This hypothesis was addressed by evaluating immune function in HESN from the Pumwani commercial sex worker cohort and HIV-controllers from the Manitoba elite controller cohort. In HESN, immune quiescence was marked by low levels of circulating activated T cells and low levels of the proinflammatory mediators IL-1α and IL-8 in the cervical mucosa. Regulatory T cells (Tregs), which suppress T cell activation, were elevated in HESN, and may represent a driver of immune quiescence. Low T cell activation and elevated Tregs were associated with reduced cellular susceptibility to infection in vitro. These data suggest that immune quiescence protects against infection by limiting the activated target CD4+ T cell pool, in support of the central hypothesis. HIV-controllers expressed low levels of the proinflammatory chemokines IP-10 and MCP-1 and low frequencies of activated T cells. These data demonstrate that immune quiescence is not only protective prior to exposure, but is also beneficial following infection. HIV-controllers also had elevated MIP-1α, reduced TGFβ and HIV-specific T cell proliferation responses, which contribute to protection by mechanisms other than immune quiescence. Taken together, these data support a role for immune quiescence in protection from HIV infection and disease progression. Mechanisms of reducing inflammation and target cell activation should be considered during future HIV vaccine and microbicide development.

Understanding natural mechanisms of protection against HIV infection and disease progression are key priorities for informing vaccine and microbicide design. The research presented in this thesis aimed to characterize mechanisms of defence in HIV-exposed seronegative (HESN) individuals, who naturally resist infection by HIV, and HIV-controllers, who are HIV-infected, but suppress viral replication in the absence of treatment. Previous studies have linked resistance to HIV infection with low basal levels of gene transcription and reduced production of inflammatory mediators, suggesting an overall state of immune quiescence in HESN. Immune quiescence may also be protective in HIV-infected individuals, as immune activation drives disease progression. The central hypothesis of this thesis is that immune quiescence protects against HIV infection and disease progression by limiting the pool of activated target CD4+ T cells susceptible to HIV infection. This hypothesis was addressed by evaluating immune function in HESN from the Pumwani commercial sex worker cohort and HIV-controllers from the Manitoba elite controller cohort. In HESN, immune quiescence was marked by low levels of circulating activated T cells and low levels of the proinflammatory mediators IL-1α and IL-8 in the cervical mucosa. Regulatory T cells (Tregs), which suppress T cell activation, were elevated in HESN, and may represent a driver of immune quiescence. Low T cell activation and elevated Tregs were associated with reduced cellular susceptibility to infection in vitro. These data suggest that immune quiescence protects against infection by limiting the activated target CD4+ T cell pool, in support of the central hypothesis. HIV-controllers expressed low levels of the proinflammatory chemokines IP-10 and MCP-1 and low frequencies of activated T cells. These data demonstrate that immune quiescence is not only protective prior to exposure, but is also beneficial following infection. HIV-controllers also had elevated MIP-1α, reduced TGFβ and HIV-specific T cell proliferation responses, which contribute to protection by mechanisms other than immune quiescence. Taken together, these data support a role for immune quiescence in protection from HIV infection and disease progression. Mechanisms of reducing inflammation and target cell activation should be considered during future HIV vaccine and microbicide development.

One of the most effective immunological interventions for human disease prevention is the administration of anti-red blood cell (RBC) IgG, more specifically, anti-D IgG, for prevention of hemolytic disease of the fetus and newborn (HDN), a serious and potentially fatal condition caused by the maternal immune response against the Rhesus (Rh) blood group system D antigen on fetal RBC. Despite its widespread clinical use, the mechanism of the suppressive anti-RBC IgG effect is not fully understood. In a murine model of immunity to foreign RBCs, transfusion of mice with IgG-opsonized RBCs strongly attenuated the antibody response compared to transfusion of untreated RBCs. This model was used to study the anti-RBC IgG effect on the host immune response. Contrary to the predominant theories of the anti-D effect, here it is shown that IgG-mediated RBC clearance is not sufficient for the attenuation of antibody responses. IgG-opsonized RBCs internalized by the mononuclear phagocytic cells could stimulate T and B cell responses against RBC antigens. This thesis also shows that the adaptive tolerance at the T or B cell level is not the reason for the attenuation of the antibody response. Instead, IgG selectively prevented the appearance of antigen-primed RBC-specific B cells and, surprisingly, induced the host B cell response against the IgG in complex with RBCs. These results suggest that the inability of RBC-specific B cells to recognize and present RBC-specific epitopes may explain the inhibitory IgG effect.

Submitted by Ana Maria Fiscina Sampaio (fiscina@bahia.fiocruz.br) on 2015-05-12T13:35:17Z No. of bitstreams: 1 Juliana Coelho Santos Isotipo...2014.pdf: 500362 bytes, checksum: 4c5dbf54877a6ef41cbbca30b73e6cde (MD5) / Approved for entry into archive by Ana Maria Fiscina Sampaio (fiscina@bahia.fiocruz.br) on 2015-05-12T13:35:26Z (GMT) No. of bitstreams: 1 Juliana Coelho Santos Isotipo...2014.pdf: 500362 bytes, checksum: 4c5dbf54877a6ef41cbbca30b73e6cde (MD5) / Made available in DSpace on 2015-05-12T13:35:26Z (GMT). No. of bitstreams: 1 Juliana Coelho Santos Isotipo...2014.pdf: 500362 bytes, checksum: 4c5dbf54877a6ef41cbbca30b73e6cde (MD5) Previous issue date: 2014 / Fundação Oswaldo Cruz. Centro de Pesquisas Gonçalo Moniz. Salvador, BA, Brasil. / Neste estudo foi analisada a distribuição de isotipos de imunoglobulinas IgG1, IgG2 e IgE envolvidas na resposta a Leishmania no soro e a expressão de mRNA para IFN-g e IL-4 in situ no baço de cães naturalmente infectados com L.infantum com diferentes perfis de susceptibilidade ou resistência à doença. A atividade sérica de anticorpos do isotipo IgG1 contra Leishmania tendeu a ser maior nos animais com teste cutêneo da Leishmanina negativo e com parasitismo esplênico (grupo infectado potencialmente susceptível, 0,424±0,401) que nos outros grupos: com teste cutêneo da Leishmanina positivo e ausência de parasitismo esplênico (grupo infectado potencialmente resistente, 0,226±0,114), ou com ambos teste cutêneo da Leishmanina e cultura esplênica positivos (grupo em fase indeterminada da doença, 0,234±0,125) ou com ambos os parâmetros negativos (grupo potencialmente não infectado, 0,159±0,044). Essa diferença não foi, contudo estatisticamente significante (ANOVA, P=0,1450). IgG2 específica anti-Leishmania foi maior (ANOVA P=0,0001) no grupo infectado potencialmente susceptível (1,324±0,322) que nos demais grupos: em fase indeterminada da doença (0,930±0,383, P=0,05), infectado potencialmente resistente (0,916±0,401, P=0,05) e potencialmente não infectado (média 0,299±0,151, P=0,001). Foi também maior nos grupos infectado potencialmente resistente e com infecção em fase indeterminada que no grupo de animais potencialmente não infectado. Não houve diferenças entre os grupos (ANOVA p=0,4) nos resultados séricos de IgE anti-Leishmania; o grupo potencialmente susceptível (0,749±0,485) tendeu a apresentar valores médios mais elevados que os grupos potencialmente resistente (0,518±0,161), ou com doença em fase indeterminada (média 0,591±0,331) ou potencialmente não infectados (0,530±0,121), essas diferenças foram intensificadas pela alta atividade de anticorpos do isotipo IgE anti-Leishmania em um dentre os 11 animais examinados, não sendo estatisticamente significante (ANOVA, P=0,4668). Não foram observadas diferenças na expressão de mRNA para IFN-g e IL-4 no baço de animais não infectados ou naturalmente infectados com L. nfantumi com (a) teste cutêneo da Leishmanina positivo e cultura esplênica negativa ou com (b) teste cutêneo da Leishmanina negativo e parasitismo esplênico. Observou-se uma preponderância de anticorpos da subclasse IgG2 em animais com parasitismo esplênico independente da resposta ao teste cutêneo da Leishmanina. Tais resultados sugerem que a polarização da resposta imune a Leishmania pode variar em diferentes compartimentos como sangue e baço. / We analyzed the distribution immunoglobulin isotypes IgG1, IgG2 and IgE involved in the response to Leishmania and the mRNA expression for IFN-g and IL-4 in situ in the spleen of dogs naturally infected with IgG1 antibody anti-Leishmania serum activity was higher in animals with negative Leishmanin skin test and splenic parasitism (infected and potencially susceptible to VL group, 0,424±0,401) than in other groups: positive Leishmanin skin test and negative splenic parasitism (infected and potentially resistant to VL group, 0,226±0,114), or both positive Leishmanin skin test and slpenic parasitism (infected with undefined susceptibility status group, 0234±0,125) or both negative parameters (non-infected group, 0159±0,044). This difference however was not statistically significant (ANOVA, P=0145). Specific IgG2 anti-Leishmania was higer (ANOVA P=0,0001) in infected and potencially susceptible to VL group (1,324±0,322) than in the other groups: infected with undefined susceptibility status (0,930±0,383, P=0,05), infected and potencially resistant to VL (0,916±0,401, P=0,05) and non infected group (0,299±0,151, P=0,001). Was also higher in infected and potencially resistant to VL and infected with undefined susceptibility status groups than in group of non-infected animals. There was no significant differences (ANOVA p=0,4) between different groups in seric IgE anti-Leishmania, infected and potencially susceptible to VL group (0,749±0,485) showed media higher than in infected and potencially resistant to VL group (0,518±0,161), or in infected with undefined susceptibility status group (0,591±0,331) or non-infected group (0,530±0,121), these differences were intensified for the higher IgE antibody activity in one between 11 examined animals, although this was not statistically significant (ANOVA, P=0,4668). There was no difference in IL-4 or IFN-g mRNA expression in the spleen among groups of animals non-infected or naturally infected with L. infantum, with (a) strong LST and negative spleen culture for the parasite or with (b) negative LST and parasite in the spleen We could observe an interesting preponderance of antibodies from the IgG2 class in animals with splenic parasitism independently of the LST response. Our results suggest that the polarity of immune response to Leishmania may vary in different compartments such as blood and spleen.

Hepatitis C virus (HCV) is remarkably efficient at evading host immunity to establish chronic infection. During chronic HCV infection, interleukin-12 (IL-12) produced by monocytes/macrophages (M/Mφ) is significantly suppressed. Programmed death-1 (PD-1), an inhibitory receptor on immune cells, plays a pivotal role in suppressing T-cell responses during chronic viral infection. To determine whether PD-1 regulates IL-12 production by M/Mφ during chronic HCV infection, we examined the expressions of PD-1, its ligand PDL-1, and their relationship with IL-12 production in M/Mφ from HCV-infected, HCV-resolved, and healthy subjects by flow cytometry. Toll-like receptor (TLR) -mediated IL-12 production by M/Mφ was selectively suppressed, while PD-1/PDL-1 expressions were up-regulated, in HCV-infected subjects compared with HCV-resolved or healthy subjects. Up-regulation of PD-1 was inversely associated with the degree of IL-12 inhibition in HCV infection. Interestingly, the reduced response of M/Mφ from HCV-infected individuals to TLR ligands appeared not to be the result of a lack of the ability to sense pathogen, but to an impaired activation of intracellular janus kinase/signal transducer and activator of transfection (STAT) pathway as represented by inhibited STAT-1 phosphorylation in M/Mφ from HCV-infected individuals compared with HCV-negative subjects. Successful HCV treatment with pegylated interferon/ribavirin or blocking PD-1/PDL-1 engagement ex vivo led to reduced PD-1 expression and improved IL-12 production as well as STAT-1 activation in M/Mφ from HCV-infected individuals. These results suggest that the PD-1 inhibitory pathway may negatively regulate IL-12 expression by limiting STAT-1 phosphorylation in M/Mφ during chronic HCV infection. No claim to original US government works.

By cross-linking B7-DC on dendritic cells (DC) the human IgM antibody (B7-DC XAb) shifts polarized immune responses from Th2 to Th1 in an antigen-specific manner. The molecular determinants governing the ability of DC to reprogram the polarity of T cell recall responses are not yet known. In addition to the expected role of T-bet expressed by T cells in regulating Th1 responses, we find using in vitro assays and an established in vivo model of allergic airway inflammation that T-bet expression by DC is also required for the polarity shift promoted by B7-DC XAb. T-bet expression by both T cells and DC is critically important for B7-DC XAb-induced down-regulation of IL-4, up-regulation of IFN-γ and suppression of allergic airway inflammation. Moreover, retroviral reconstitution of T-bet expression in T-bet-deficient DC rescued their ability to modulate both naive and memory T-cell responses from Th2 to Th1. Our observations further our understanding of the critical mediators controlling the ability of DC to modify the responses of previously activated T cells and reveal the interesting use of the same transcription factor to regulate the inductive phenotype of DC and the inducible phenotype of T cells.

京都大学 / 0048 / 新制・課程博士 / 博士(生命科学) / 甲第20533号 / 生博第375号 / 新制||生||50(附属図書館) / 京都大学大学院生命科学研究科高次生命科学専攻 / (主査)教授 杉田 昌彦, 教授 米原 伸, 教授 清水 章 / 学位規則第4条第1項該当 / Doctor of Philosophy in Life Sciences / Kyoto University / DFAM

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