Deletion is neither sufficient nor necessary for the induction of peripheral tolerance in mature CD8+ T cells

Previous reports have demonstrated clonal deletion of CD8(+) T cells during peripheral tolerance induction to tissue antigens. However, direct evidence demonstrating a causal connection between deletion and tolerance has not been reported because of model limitations in which the tissue antigens were expressed in vital organs. Thus, studies were initiated in a mouse model where expression of a membrane-bound ovalbumin fusion protein (mOVA) was driven by a prostate specific androgen regulated probasin promotor, providing restricted expression in a non-vital organ where antigen levels can be abrogated through androgen deprivation. Adoptive transfer of mOVA specific CD8(+) T cells (OT-I) was used to assess the development of peripheral tolerance. Proliferation of OT-I cells was observed, as was partial deletion of transferred OT-I cells. Although deletion occurred, the long-term persistence of a stable level of OT-I cells was observed. Importantly, the persistent OT-I cells lost antigen responsiveness within 3 weeks of transfer. Castration resulted in loss of high-level prostate mOVA expression, with a resultant abrogation of tolerance induction, but surprisingly did not affect the deletion rate of OT-I cells. In contrast, abrogation of deletion through the adoptive transfer of OT-I cells from third generation CD95-deficient mice had no effect on tolerance induction. These data demonstrate the necessity for continued expression of tissue antigen throughout the establishment of peripheral tolerance. Furthermore, these findings demonstrate that deletion is neither sufficient nor required for CD8(+) T-cell tolerance to tissue antigens, suggesting that regulatory events independent of deletion are necessary for peripheral tolerance induction to prostate antigens.     

Blockade of T cell costimulatory signals using adenovirus vectors prevents both the induction and the progression of experimental autoimmune myocarditis

Experimental autoimmune myocarditis (EAM) has been used as a model for human myocarditis in relation to the autoimmune mechanism and proved to be a T cell-mediated autoimmune disease. Interactions of T cell surface receptors CD28 and CD40L with their ligands B7 and CD40, respectively, on APCs are critical for antigen-specific T cell activation under physiological and pathological conditions. To achieve effective inhibition of these interactions, we have constructed adenovirus vectors containing CTLA4Ig (AdexCTLA4Ig) and CD40Ig (AdexCD40Ig) and examined the effects of these adenovirus vectors in preventing EAM. AdexLacZ as a control, or AdexCTLA4Ig and/or AdexCD40Ig were injected intravenously into rats on day 0 or 14 after immunization to study the preventive effects on EAM in the T cell activation phase or inflammatory phase. Disease severity was estimated by the macroscopic and microscopic findings of the heart, heart weight to body weight ratios, and cellular and humoral immune responses on day 21. The onset of EAM after AdexCTLA4Ig or AdexCD40Ig treatment on day 0 was completely inhibited and antigen-specific lymphocyte proliferation was significantly reduced in those adenovirus-treatment groups, suggesting that those therapies induce antigen-specific T cell anergy. Moreover, significant reduction in disease severity was achieved after the adenovirus vector treatment even on day 14 compared with EAM rats. This study indicates the therapeutic potential of costimulatory pathway blockade by gene-transfer in myocarditis.     

Differing antibody IgG isotypes in the polar forms of leprosy and cutaneous leishmaniasis characterized by antigen-specific T cell anergy.

Leprosy and American cutaneous leishmaniasis are tropical diseases which present a spectrum of clinical and immunological manifestations. Lepromatous leprosy and diffuse cutaneous leishmaniasis are the severe, progressive polar forms of disease characterized by persistent T cell anergy. Relative concentrations of antibodies belonging to the four IgG isotypes have been determined in these forms of disease as well as active visceral leishmaniasis, which presents transitory T cell anergy. Leishmania-specific IgG4 antibodies predominated in 19/20 sera from patients with diffuse cutaneous leishmaniasis, and IgG1 antibodies predominated in 9/10 cases of untreated visceral leishmaniasis. The predominant IgG isotype of Mycobacterium leprae-specific antibodies in untreated lepromatous leprosy was remarkably variable (IgG1, IgG2, IgG3 and IgG4 in 8, 6, 2 and 1 sera, respectively). Differing IgG antibody isotypes have been associated with distinct CD4+ T cell helper subpopulations and their characteristic lymphokine profiles in several pathologies. These results suggest that T cell anergy in chronic intracellular infections may be associated with as yet undefined mechanisms which modulate reported T helper cell-lymphokine isotype relationships.     

Immune and serologic profiles of HIV-infected and noninfected hemophilic children and adolescents

Objectives: To assess relationships among the effects of HIV on hemophilic children and adolescents' immunologic parameters and vaccine-related serology. Methods: We analyzed data from extensive baseline immunologic evaluations of 207 HIV antibody-positive (HIV+) and 126 HIV antibody-negative (HIV?) hemophilic children and adolescents. Results: HIV+ and HIV- participants differed significantly in T-lymphocyte subpopulation numbers, immunoglobulin levels, and seroprevalence rates for diphtheria toxoid, measles, and mumps antigens. IgG levels, IgM levels, and serologic titers to vaccine antigens showed little correlation with T-cell parameters. Proportionately more HIV+ participants were nonreactive to each and all of a panel of 7 skin test antigens (71 % vs 28% anerglc, RR 2.6). The odds of anergy increased 1.6 times for every decline of 200 CD4 ± cells/μTl. Conclusions: HIV had significant, largely independent T- and B-lymphocyte effects on this pediatric cohort. © 1994 Wiley-Liss, Inc.     

Maternal-fetal interaction: preconception immunization in mice prevents neonatal sensitization induced by allergen exposure during pregnancy and breastfeeding

Allergen exclusion measures during pregnancy and lactation have been given consideration in studies of primary allergy prevention but complete avoidance of mother/neonatal allergen exposure has proven to be a difficult procedure. To evaluate a strategy to prevent allergen sensitization in early life in mice, we first established a neonatal model with ovalbumin sensitization through maternal allergen exposure during pregnancy or breastfeeding. The modulatory potential of preconception immunization was investigated on the neonatal development of subsequent allergic responses to maternal allergen exposure. Herein, we demonstrate that immunized mothers exposed to antigen during pregnancy or breastfeeding underwent intense vertical transmission of antibodies, including immunoglobulin G (IgG) in complex with ovalbumin and IgG1 antibody with anaphylactic function. It was further shown that maternal immunization efficiently decreased the passage of free antigens through breastfeeding and inhibited the enhanced IgE antibody response after postnatal antigen exposure. In addition, antenatal immunization decreased the antigen-specific proliferative response of immunized neonates, in parallel with profound downmodulatory effects on both the activation and differentiation of T and B cells after a non-specific stimulus and cytokine production. These findings showed that early life sensitization, subsequent to maternal allergen exposure during both the prenatal and postnatal periods, could be avoided by preventive vaccination of the mother.     

Normal human pregnancy is associated with an elevation in the immune suppressive CD25+ CD4+ regulatory T-cell subset

Summary CD4+ CD25+ T regulatory cells (TReg), suppress antigen-specific immune responses and are important for allograft tolerance. During pregnancy the mother tolerates an allograft expressing paternal antigens (the fetus) requiring substantial changes in immune regulation over a programmed period of time. We analysed whether immune-suppressive TReg cells were altered during pregnancy and therefore might play a part in this tolerant state. The presence of TReg cells was assessed in the blood of 25 non-pregnant, 63 pregnant and seven postnatal healthy women by flow cytometry. We observed an increase in circulating TReg cells during early pregnancy, peaking during the second trimester and then a decline postpartum. Isolated CD25+ CD4+ cells expressed FoxP3 messenger RNA, a marker of TReg cells, and suppressed proliferative responses of autologous CD4+ CD25- T cells to allogeneic dendritic cells. These data support the concept that normal pregnancy is associated with an elevation in the number of TReg cells which may be important in maintaining materno-fetal tolerance.