Suppression of antibody response and prolongation of skin graft survival by multiple blood transfusions in the rat

Molecular mechanisms for adaptive tolerance and other T cell anergy models

Since the original description of T cell anergy in CD4 clones from mice and humans, a number of different unresponsive states have been described, both in vivo and in vitro, that have been called anergic. While initial attempts were made to understand the similarities between the different models, it has now become clear from biochemical experiments that many of them have different molecular mechanisms underlying their unresponsiveness. In this review we will detail our own work on the in vivo model referred to as adaptive tolerance and then attempt to compare this biochemical state to the multitude of other states that have been described in the literature.

Antigen-Induced Unresponsiveness Results in Altered T Cell Signaling

Pretransplant exposure to allogeneic lymphocytes can result in donor-specific unresponsiveness and prolonged allograft survival. Intracellular signaling events have been described in anergic T cell clones, but the biochemical events underlying in vivo induced unresponsiveness have not been studied in detail. We employed a TCR transgenic mouse, bearing the 2C TCR, providing adequate numbers of homogenous peripheral T cells to study biochemical aspects of T cell unresponsiveness in vivo. 2C mice exposed to semiallogeneic lymphocytes (H-2b × H-2d) experienced prolonged H-2d cardiac allograft survival, and cells from these mice did not proliferate or make IL-2 in response to alloantigen (H-2d). Importantly, there were marked differences in TCR-associated tyrosine phosphorylation activation patterns. The targets for the unresponsive state appear to be diminished Lck activation and absent ZAP-70 and LAT (linker for activation of T cells) phosphorylation. Our study demonstrates that Ag-induced tolerance in vivo is accompanied by altered early TCR-mediated signaling events.

Induction of transplantation tolerance by intravenous injection of allogeneic lymphocytes across an H-2 class II mismatch. Different mechanisms operate in tolerization across an H-2 class I vs. H-2 class II disparity

Previously, we have shown that the intravenous (i.v.) injection of allogeneic lymphocytes across an H-2 class I-mutant disparity leads to specific skin allograft tolerance caused by irradiation-sensitive donor T cells, which function as veto cells. In the present study, we show that the i.v. injection of H-2 class II-incompatible spleen cells also results in specific skin allograft tolerance. However, tolerance induction depends on the presence of irradiation-resistant non-T cells in the donor cell inoculum. Thus, different mechanisms operate in tolerance induction across an H-2 class I vs. H-2 class II mismatch. I.v. injection of allogeneic spleen cells across an H-2 class I plus class II disparity does not result in skin allograft tolerance. Finally, our data show that transfusion-induced suppression of the delayed-type hypersensitivity response against alloantigens does not correlate with skin allograft tolerance induced by i.v. injected allogeneic lymphocytes. In conclusion, the type of H-2 mismatch between transfusion donor and recipient not only determines the occurrence of allograft tolerance but also the mechanism leading to tolerization.

MLC-inhibiting serum in mice after transfusion with 3 M KCl-extracted soluble antigen

Balb/c (H-2d) mice were transfused weekly with 3 M KCl-extracted soluble antigen prepared from splenocytes of C3H/HeJ (C3H)(H-3k) mice. One week after each transfusion, spleen and serum samples were collected from transfused mice and pooled. The serum was absorbed with erythrocytes and spleen cells from C3H mice and heat inactivated. Spleen cells from transfused mice were tested for proliferative responses in mixed lymphocyte culture (MLC) against stimulator cells from the antigen donor C3H or from third party SJL (H-2s) mice. The proliferative responses of lymphocytes from soluble-antigen-transfused Balb/c mice to stimulator cells from C3H and SJL mice were not suppressed. Furthermore, suppressor cells could not be demonstrated in spleens of transfused mice in in vitro coculture experiments. The MLC inhibition test was utilized to investigate the presence of MLC-inhibiting serum from transfused mice. The results demonstrate that serum capable of inhibiting responses of Balb/c mice were induced after three weekly injections of soluble antigen and that this inhibition in MLC was specific for the stimulator cells from the antigen donor C3H mice. These findings differ from our studies using whole blood transfusions where (1) MLC inhibiting antibodies developed in Balb/c mice after only one transfusion of C3H whole blood, and (2) serum from blood transfused mice achieve greater inhibition than soluble-antigen-induced serum. These results suggest that although soluble antigen is capable of inducing MLC inhibiting serum, the kinetics of this induction may be different from transfusion with whole blood.