Luiz Stark Aroeira

Anti-γδ T cell antibody blocks the induction and maintenance of oral tolerance to ovalbumin in mice

Abstract The oral administration of antigens is one of the means of inducing tolerance in adult mammals. In this report, the role of γδ T cells in the induction and maintenance of orally-induced tolerance to ovalbumin was investigated. The injection of a monoclonal anti-γδ T cell monoclonal antibody blocked the induction of oral tolerance, because the secondary immune responses to ovalbumin in these animals were comparable to the corresponding responses in ovalbumin-immunized control mice. Furthermore, depletion of γδ T cells either in vivo or in vitro abolished already established oral-tolerance. The fact that the state of tolerance could be adoptively transferred to naive recipients by CD3+αβ−γδ+ spleen cells from tolerant mice. These results suggest that systemic oral tolerance is induced and actively maintained by mechanisms involving γδ T cells.

Anti‐IL‐10 Treatment Does Not Block Either the Induction or the Maintenance of Orally Induced Tolerance to Ova

Herein, the role of IL‐10 in the induction and maintenance of oral tolerance was evaluated. The results show that: (1) mice treated with MoAb anti‐IL‐10 are permissive to the induction of oral tolerance to OVA; (2) anti‐IL‐10 treatment did not reverse the in vitro blocking of T cell proliferative response found in orally‐tolerized mice; and (3) orally‐induced tolerance could not be broken by anti‐IL‐10 treatment. Taken together, these results suggest that IL‐10 is not a fundamental cytokine for the establishment and maintenance of oral tolerance.

B cells modulate T cells so as to favour T helper type 1 and CD8 + T-cell responses in the acute phase of Trypanosoma cruzi infection

In this study, we have evaluated the production of pro‐ and anti‐inflammatory cytokines and the formation of central and effector memory T cells in mice lacking mature B cells (muMT KO). The results show that Trypanosoma cruzi infection in C57Bl/6mμ MT KO mice is intensified in relation to control mice and this exacerbation is related to low levels of inflammatory cytokines produced during the acute infection and the lower numbers of central and effector memory CD4+ and CD8+ T cells generated during the acute phase of the infection. In addition, a marked reduction in the CD8+ T‐cell subpopulation was observed in muMT KO infected mice. In agreement to this, the degree of tissue parasitism was increased in muMT mice and the tissue inflammatory response was much less intense in the acute phase of the infection, consistent with a deficit in the generation of effector T cells. Flow cytometry analysis of the skeletal muscle inflammatory infiltrate showed a predominance of CD8+ CD45Rb low in B‐cell‐sufficient C57Bl/6 mice, whereas the preponderant cell type in muMT KO skeletal muscle inflammatory infiltrate was CD4+ T cells. In addition, CD8+ T cells found in skeletal muscle from muMT KO infected mice were less activated than in control B‐cell sufficient infected mice. These results suggest that B cells may participate in the generation of effector/memory T cells. In addition and more importantly, B cells were crucial in the maintenance of central and effector memory CD8+ T cell, as well as the determination of the T cell cytokine functional pattern, and they may therefore account for critical aspects of the resistance to intracellular pathogens, such as T. cruzi.

The role of IL-4 in the staphylococcal enterotoxin B-triggered immune response: increased susceptibility to shock and deletion of CD8Vβ8+ T cells in IL-4 knockout mice

Administration of superantigens in vivo triggers responding T cells into clonal expansion and subsequent activation of the programmed cell death pathway, as well as into anergy. We examined the possibility that Th1 cytokines are involved in rescue from superantigen‐induced programmed cell death and prevention of anergy by studying the Staphylococcus aureus enterotoxin B (SEB) immune response in mice in which the IL‐4 gene was deleted (IL‐4–/–). In these mice, Th1 cell activation triggers increased IFN‐γ and reduced IL‐5 production as compared to IL‐4+/+ mice. The primary anti‐SEB antibody response in IL‐4–/– mice is thus dominated by immunoglobulins of the IgG2a isotype, whereas the IgG1 isotype prevails in IL‐4+/+ mice. Our results also show that, in contrast to expectations, IL4–/– mice are more susceptible to SEB plus low‐dose D‐galactosamine‐induced shock and that this response is TNF‐α‐dependent. In vivo treatment induces partial deletion and anergy of remaining SEB‐reactive T cells. During the SEB‐induced response, CD4Vβ8+ T cells are deleted in IL‐4–/– mice, but not in IL‐4+/+ mice, suggesting a function for IL‐4 in CD8+ T cell rescue from apoptosis. We show that IL‐4 efficiently protects CD8+ T cells from in vitro starvation‐induced apoptosis, and conclude that IL‐4 has an important role in Th1 immune response regulation.

Anti‐Vβ8 antibodies induce and maintain staphylococcal enterotoxin B‐triggered Vβ8+ T cell anergy

The mechanism involved in the maintenance of staphylococcal enterotoxin B (SEB)‐induced T cell anergy is poorly understood. We demonstrated earlier that B cells play an important role in the maintenance of SEB‐induced T cell anergy in vivo and in vitro. Here, we demonstrate that B cells are not essential in SEB‐induced T cell activation, but are important for the maintenance of T cell memory phenotype and anergy in vivo. Studying the activated B cell repertoire, we observe that SEB treatment increases serum anti‐Vβ8 antibody titer as detected by enzyme‐linked immunosorbent assay using soluble Vβ8 chains as antigens, and by staining of a Vβ8‐expressing thymoma. These antibodies disappear gradually after immunization with SEB, whereas the capacity of the T cells to respond to SEB in vitro is restored. Anti‐Vβ8 monoclonal antibody treatment causes Vβ8+ T cell unresponsiveness to SEB in vitro (anergy), without affecting CD4Vβ8+ T cell frequency. Together, these results suggest a new mechanism to explain the maintenance of SEB‐induced T cell anergy, which is dependent on B cells and on anti‐Vβ8 antibody that specifically interacts with Vβ8+ T cells.

T CELL-DEPENDENT ANTIBODY RESPONSE TO STAPHYLOCOCCAL ENTEROTOXIN B

Treatment of mice with staphylococcal enterotoxin B (SEB) induces specific T‐cell tolerance to this superantigen, characterized by partial deletion of Vβ8+ T cells in vivo and T cell anergy in vitro. In this study we examined the humoral response to SEB in BALB/c mice. Immunization of mice with SEB results in a detectable anti‐SEB antibody response. Upon further treatment of mice with SEB, specific antibody levels increase significantly and the response is accelerated—characteristics of a secondary humoral response. The secondary antibody response is T cell dependent, can be transferred to T cell deficient mice with splenocytes and is composed mainly of IgM, IgG1 and IgG2b isotypes, suggesting that Th2 cells provide B cell help in this response. These data demonstrate that at the same time as inducing in vitro unresponsiveness, SEB primes SEB‐specific T helper cells to provide help for B cells in a secondary antibody response.

The development of humoral immunological memory to a T-cell-dependent antigen requires thymic emigrant cells.

Immunological memory is embodied in the rapid and enhanced immune responsiveness to previously encountered antigens. Classically, memory would depend on the presence of small resting long-lived specific lymphocytes which, through clonal expansion after priming with antigen, would be present at higher frequencies than in naive animals. Here we report that T-cell-reconstituted athymic mice, which lack recent thymic emigrants, mount a primary response to a T-cell-dependent antigen, but do not develop memory or the capacity to produce specific anti-TNP IgG1 antibodies during the secondary immune response. On the other hand, if thymocytes are continuously provided during the secondary response, a typical secondary immune response is achieved with high levels of specific IgG1. These results lead us to propose that the development of humoral immunological memory cannot be explained solely by the long life span of primed T lymphocytes, but is rather a dynamic state dependent on the continuous presence of recent thymic emigrants and qualitative functional differences in responder T cells.