Masanori Niimi

IL-10 Is Required for Regulatory T Cells to Mediate Tolerance to Alloantigens In Vivo

We present evidence that donor-reactive CD4+ T cells present in mice tolerant to donor alloantigens are phenotypically and functionally heterogeneous. CD4+ T cells contained within the CD45RBhigh fraction remained capable of mediating graft rejection when transferred to donor alloantigen-grafted T cell-depleted mice. In contrast, the CD45RBlow CD4+ and CD25+CD4+ populations failed to induce rejection, but rather, were able to inhibit rejection initiated by naive CD45RBhigh CD4+ T cells. Analysis of the mechanism of immunoregulation transferred by CD45RBlow CD4+ T cells in vivo revealed that it was donor Ag specific and could be inhibited by neutralizing Abs reactive with IL-10, but not IL-4. CD45RBlow CD4+ T cells from tolerant mice were also immune suppressive in vitro, as coculture of these cells with naive CD45RBhigh CD4+ T cells inhibited proliferation and Th1 cytokine production in response to donor alloantigens presented via the indirect pathway. These results demonstrate that alloantigen-specific regulatory T cells contained within the CD45RBlow CD4+ T cell population are responsible for the maintenance of tolerance to donor alloantigens in vivo and require IL-10 for functional activity.

Visualization of the in vivo generation of donor antigen-specific effector CD8+ T cells during mouse cardiac allograft rejection: in vivo effector CD8+ T cell generation during allograft rejection.

BACKGROUND An adoptive transfer system was used to study the fate of alloreactive CD8+ H-2Kb-specific TCR transgenic (DES+) T cells in vivo after transplantation. METHODS A trace population of 2.0x10(6) CD8+DES+ T cells were adoptively transferred into syngeneic CBA.Ca (H-2k) mice 24 hr before transplantation of an H-2Kb+ or H-2Kb- cardiac allograft. RESULTS H-2Kb specific T cells proliferated and produced interleukin-2 and interferon-gamma in response to H-2Kb+, but not H-2Kb- cardiac allografts. CD8+DES+ T cells that infiltrated the H-2Kb+ cardiac allografts developed a distinct cell surface and cytokine phenotype compared with the CD8+DES+ T cells that remained in the periphery. H-2Kb-specific graft infiltrating T cells (a) underwent a larger number of cell divisions (> =3), (b) increased in size, (c) up-regulated CD69, and (d) down-regulated CD62L. CONCLUSIONS These results demonstrate that alloantigen-specific T cells can be monitored in vivo during the immune response to an allograft and that the fate of CD8+ T cells specific for the allogeneic class I molecules expressed by the graft is different between cells in the periphery and those that infiltrate the graft.

Intrathymic administration of B cells induces prolonged survival of fully allogeneic cardiac grafts without prolonged deletion of donor-specific thymocytes

Intrathymic (IT) injection of alloantigen has been shown to induce unresponsiveness to allografts although the exact mechanisms of tolerance induction remains unclear. C57BL/10 (H2b) cardiac allografts were accepted in C3H/He (H2k) mice pretreated with IT inoculation of donor splenocytes (1 x 10(6)) in combination with a depleting anti-CD4 monoclonal antibody 27 days before cardiac transplantation. To investigate which cell types were responsible for tolerance induction by IT injection of alloantigen, resting B (rB) cells or dendritic cells were used as the thymic inoculum instead of whole splenocytes. IT injection of rB cells induced indefinite graft prolongation in all recipients while only 20% of mice that had received IT injection of dendritic cells accepted grafts for over 100 days. In contrast, IT injection of dendritic cells resulted in significant deletion of donor-specific thymocytes whereas rB cells were relatively ineffective. IT deletion is not essential for the induction of tolerance by IT injection of rB cells; nondeletional mechanisms can be involved.

Immunoregulation by CD4 T cells in the induction of specific immunological unresponsiveness to alloantigens in vivo: evidence for a reduction in the frequency of alloantigen-specific cytotoxic T cells in vitro☆

Donor-specific unresponsiveness to allogeneic cardiac allografts in mice can be induced by the combined pretreatment with donor alloantigen and anti-CD4 antibody (anti-CD4+DST). We have investigated whether the induction of unresponsiveness in this model is due to the presence of T cells that regulate immune responsiveness towards the allograft. First, we analysed the functional characteristics of splenocytes from pretreated mice at the time of transplantation. A significant reduction in the frequency of donor specific cytotoxic precursor was found only after the anti-CD4+DST treatment. Next, we designed an in vitro assay to identify the phenotype of the splenocyte population responsible. CD4+ and CD4- fractions were purified from mice treated with anti-CD4+DST or anti-CD4 alone (controls) by cell sorting. Interestingly, only the addition of CD4+ cells from anti-CD4+DST treated mice resulted in a selective reduction and a bimodal distribution in the donor specific CTLp response, indicating the presence of a regulatory population. CD4+ cells from controls did not have this effect. These in vitro findings were substantiated by adoptive transfer experiments in vivo. These data demonstrate that CD4+ cells with the ability to regulate immune responsiveness to a cardiac allograft are present at the time of transplantation following pretreatment with donor alloantigen in combination with anti-CD4.

Evidence that non-deletional mechanisms are responsible for inducing and maintaining unresponsiveness after Intrathymic injection of non-professional antigen presenting cells

INTRODUCTION Intrathymic inoculation of donor alloantigen and concomitant immunosuppressive treatment can induce immune unresponsiveness to alloantigen. To examine the role of non-deletional mechanisms in the development of unresponsiveness, fractionated splenocytes were injected into only 1 lobe of the thymus. METHODS AND RESULTS Untreated CBA (H2(k)) mice or controls pre-treated with anti-CD4 monoclonal antibody alone (on Day -28 and -27 relative to transplantation) acutely rejected C57BL/10 (H2(b)) cardiac allografts. Intrathymic inoculation of unfractionated splenocytes, resting B (rB) cells, or dendritic cells into both thymic lobes with the antibody resulted in indefinite survival of cardiac allografts. In contrast, when donor rB cells or dendritic cells were delivered into a single lobe of the thymus with the antibody, only rB cells induced indefinite prolongation of graft survival; unfractionated splenocytes or dendritic cells were markedly less effective. Mice that had 1 of the 2 thymic lobes removed were able to reject grafts even when treated with the antibody 27 days before transplantation. Therefore, T-cell export from 1 thymic lobe was sufficient to induce graft rejection. Finally, adoptive transfer of splenocytes from mice with long-term surviving primary grafts resulting from the intrathymic injection of rB cells significantly prolonged a graft from the same donor strain in a naive syngeneic recipient. CONCLUSION Taken together, these data suggest that regulatory mechanisms generated by intrathymic injection of a non-professional antigen presenting cell, in this study donor rB cells, suppressed the rejection response mediated by T cells exported from the uninjected lobe.

Intrathymic inoculation of donor B cells prolongs cardiac allograft survival by non-deletional mechanisms

Resting B (rB) cells and splenic dendritic cells (DCs) were purified from splenocytes as described. A typical preparation of rB cells as analysed by flow cytometry was found to be 95.7% major histocompatibility class (MHC) II, 1.2% CD80, 2.5% CD86, and 92.3% sIg. A typical preparation of splenic DCs was 92.2% MHC II, 68.8% CD80, 88.2% CD86, 68% N418, and 9.4% sIg. In functional assays, DCs but not rB cells were able to stimulate proliferation of allogeneic T cell and generate cytotoxic T cells. T cells were made from spleen using a nylon wool column as described and were sorted negatively by FACS Vantage with turbo sort option (Becton Dickinson, Mountain View, Calif). Typical preparations as analysed by FACS was found to be .90% CD3, ,0.5% IA, and ,1% Ig.