José Mengel

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.

Prevention of lung eosinophilic inflammation by oral tolerance

Airway inflammation plays a major role in human asthma. Increasing evidence points to a close correlation between eosinophil infiltration and allergic lung disease. A new murine model of eosinophilic lung inflammation has recently been developed; it consists of immunizing mice with small fragments of solidified hen egg white implanted (EWI) into the subcutaneous tissue. In this model, which is further characterized here, mice challenged with ovalbumin (OVA) present an intense and persistent lung eosinophilia, as well as histopathological findings that resemble human asthma. In the present work, the effect of oral tolerance on the development of allergic lung inflammation in B6 mice immunized with antigen plus adjuvant or with EWI is investigated. It was found that in mice rendered orally tolerant by previous exposure to antigen in the drinking water, the T-helper type 2 cell (Th2)-associated allergic responses in both protocols of immunization were almost completely abolished. The allergic responses were assessed by pulmonary and bone marrow eosinophilia, lung histopathology and antigen-specific IgE and IgG1 production. These findings provide the first indication that Th2-associated lung pathology can be prevented by oral tolerance.

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.

NK1.1+ cells and T-cell activation in euthymic and thymectomized C57BL/6 mice during acute Trypanosoma cruzi infection

Natural killer (NK) cells may provide the basis for resistance to Trypanosoma cruzi infection, because the depletion of NK1.1 cells causes high levels of parasitemia in young C57Bl/6 mice infected with T. cruzi. Indeed, NK1.1 cells have been implicated in the early production of large amounts of interferon (IFN)‐γ, an important cytokine in host resistance. The NK1.1 marker is also expressed on special subpopulations of T cells. Most NK1.1+ T cells are of thymic origin, and their constant generation may be prevented by thymectomy. This procedure, by itself, decreased parasitemia and increased resistance in young mice. However, the depletion of NK1.1+ cells by the chronic administration of a monoclonal antibody (MoAb) (PK‐136) did not increase the parasitemia or mortality in thymectomized C57Bl/6 mice infected with T. cruzi (Tulahuen strain). To study the cross‐talk between NK1.1+ cells and conventional T cells in this model, we examined the expression of activation/memory markers (CD45RB) on splenic CD4+ and CD8+ T cells from young euthymic or thymectomized mice with or without depletion of NK1.1+ cells and also in aged mice during acute infection. Resistance to infection correlated with the amount of CD4+ T cells that are already activated at the moment of infection, as judged by the number of splenic CD4+ T cells expressing CD45RB−. In addition, the specific antibody response to T. cruzi antigens was precocious and an accumulation of immunoglobulin (Ig)M with little isotype switch occurred in euthymic mice depleted of NK1.1+ cells. The data presented here suggest that NK1.1+ cells have important regulatory functions in euthymic, but not in thymectomized mice infected with T. cruzi. These regulatory functions include a helper activity in the generation of effector or activated/memory T cells.

Chronic chagasic myocarditis pathogenesis: dependence on autoimmune and microvascular factors

A patogenese da miocardite chagasica cronica permanece incompletamente compreendida. Diferentes hipoteses tem sido propostas: (1) lesao direta do tecido pelo Trypanosoma cruzi;(2) teoria neurogenica; (3) reacoes imunologicas anti-miocardio; e (4) doenca microvascular. Apresentamos, no presente trabalho, uma hipotese alternativa. Acreditamos que o desenvolvimento da miocardite esta relacionado a necrose celular focal progressiva e acumulativa, associada a fibrose intersticial reparativa e reativa e hipertrofia miocitaria circunjacente. Esses processos seriam iniciados e perpetuados por fatores autoimunes e alteracoes na microcirculacao do miocardio. Esse mecanismo fisiopatogenico teria possiveis implicacoes em futuras estrategias terapeuticas no tratamento do paciente chagasico cronico visando otimizar o tratamento medico e auspiciosamente melhorar o prognostico.The pathogenesis of chronic chagasic myocarditis remains incompletely understood. Several hypotheses have been proposed: (1) direct tissue destruction by Trypanosoma cruzi; (2) neurogenic theory; (3) anti-heart immune reactions; and (4) microvascular disease. We present herein a dynamic alternative hypothesis. We believe that the development of myocarditis is related to progressive and additive focal cellular necrosis, and associated reactive and reparative myocardial fibrosis and surrounding myocytes hypertrophy. These processes may be initiated and perpetuated by autoimmune factors and alterations in the myocardial microcirculation. This could imply future therapeutic strategies in the management of chronic chagasic patients to optimize the medical treatment and hopefully improve the prognosis.The pathogenesis of chronic chagasic myocarditis remains incompletely understood. Several hypotheses have been proposed: (1) direct tissue destruction by Trypanosoma cruzi; (2) neurogenic theory; (3) anti-heart immune reactions; and (4) microvascular disease. We present herein a dynamic alternative hypothesis. We believe that the development of myocarditis is related to progressive and additive focal cellular necrosis, and associated reactive and reparative myocardial fibrosis and surrounding myocytes hypertrophy. These processes may be initiated and perpetuated by autoimmune factors and alterations in the myocardial microcirculation. This could imply future therapeutic strategies in the management of chronic chagasic patients to optimize the medical treatment and hopefully improve the prognosis.

Mouse ear spleen grafts: a model for intrasplenic immunization with minute amounts of antigen

The production of monoclonal antibodies to protein antigens which can only be obtained in tiny amounts has been a major task, since classical in vivo immunization procedures are not always efficient. In order to circumvent this problem, two methods have been developed: (1) in vitro immunization, in which the immunogen is presented directly to spleen cell cultures; (2) intrasplenic immunization, a technique in which the immunogen is deposited in the spleen tissue. The latter approach requires less laboratory work and the risk of contamination, often a problem with in vitro cultures (Nilsson and Larsson, Immunol. Today (1990) 11, 10), is greatly reduced. Here, we describe a novel method of grafting neonatal spleens in the pinna of the mouse ear. Histological and functional studies show that these spleen grafts have white and red pulp and contain normal percentages of functional T and B cells. The results indicate that this procedure is extremely efficient in priming mice for a secondary humoral immune response, since very small amounts of soluble antigen (ovalbumin) were required. The data are discussed in terms of the advantages of this new technique over current procedures for intrasplenic immunization.

Natural killer T cells are required for the development of a superantigen‐driven T helper type 2 immune response in mice

We show, here, that one single injection or weekly injections of staphylococcal enterotoxin B (SEB), starting in 1‐day‐old newborn mice, induced a powerful immune response with a T helper type 2 (Th2) pattern, as judged by the isotype and cytokine profile, with the production of large amounts of SEB‐specific immunoglobulin G1 (IgG1), detectable levels of SEB‐specific IgE and increased production of interleukin‐4 by spleen cells. These protocols also induced an increase in the levels of total IgE in the serum. Memory of SEB was transferred to secondary recipients by using total spleen cells from primed animals. The secondary humoral response in transferred mice was diminished if spleen cells from SEB‐treated mice were previously depleted of CD3+ or Vβ8+ T cells or NK1.1+ cells. In vivo depletion of NK1.1+ cells in adult mice resulted in a marked reduction in the SEB‐specific antibody response in both the primary and secondary immune responses. Additionally, purified NK1.1+ T cells were able to perform SEB‐specific helper B‐cell actions in vitro and in vivo. These results suggest that NK1.1+ T cells are required for the full development of humoral immunological memory, whilst making neonatal tolerance to SEB unachievable.

MODULATION OF THE SEVERITY OF EXPERIMENTAL AUTOIMMUNE ENCEPHALOMYELITIS BY γδ T LYMPHOCYTES ACTIVATED BY MYCOBACTERIAL ANTIGENS

Immunity to mycobacterial antigens may contribute to the maintenance of self-tolerance. Exposure of the immune system to mycobacterial antigen might well stimulate the immune system to exert control over unwanted self-reactive clones. We demonstrated that in vivo administration of Mycobacterium tuberculosis, PPD, and PPD peptide (180–196) prior to immunization with Myelin Basic Protein (MBP)led to a moderate increase of γδ T cells, suppression of the immune response, and reduction in the severity of Experimental Autoimmune Encephalomyelitis. The immunosuppression observed is due, at least in part, to the production of Transforming growth factor-β (TGFβ) by the γδ T lymphocytes.

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.

The Interleukin-17 (IL-17) puzzle in Chagas disease

In this article, we discuss an alternative explanation for the fact that the production nand plasma levels of IL-17 are diminished in patients chronically infected with nTrypanosoma cruzi, suffering from congestive heart failure. This alternate hypothesis nconsiders the inhibitory pharmacological action of digoxin, a drug commonly used to ntreat heart failure. We believe this is a significant point to be further studied as IL-17 nwas initially considered to be heart-protective. Therefore, our argument has profound ntherapeutic implications