Allosuppression: evidence for the involvement of both "noncytotoxic" and cytotoxic T cells

Analysis of the underlying cellular mechanisms of anti-CD154-induced graft tolerance: the interplay of clonal anergy and immune regulation

Although it has been shown that CD4(+)CD25(+) regulatory T cells (T(reg)) contribute to long-term graft acceptance, their impact on the effector compartment and the mechanism by which they exert suppression in vivo remain unresolved. Using a CD4(+) TCR transgenic model for graft tolerance, we have unveiled the independent contributions of anergy and active suppression to the fate of immune and tolerant alloreactive T cells in vivo. First, it is shown that anti-CD154-induced tolerance resulted in the abortive expansion of the alloreactive, effector T cell pool. Second, commensurate with reduced expansion, there was a loss of cytokine production, activation marker expression, and absence of memory T cell markers. All these parameters defined the tolerant alloreactive T cells and correlated with the inability to mediate graft rejection. Third, the tolerant alloreactive T cell phenotype that is induced by CD154 was reversed by the in vivo depletion of T(reg). Reversal of the tolerant phenotype was followed by rapid rejection of the allograft. Fourth, in addition to T(reg) depletion, costimulation of the tolerant alloreactive T cells or activation of the APC compartment also reverted alloreactive T cell tolerance and restored an activated phenotype. Finally, it is shown that the suppression is long-lived, and in the absence of anti-CD154 and donor-specific transfusion, these T(reg) can chronically suppress effector cell responses, allowing long-lived graft acceptance.

Suppression of GvHR by in vitro allogeneically stimulated lymphocytes: the role of lymphoblasts in the regulation of a primary T-cell response

Graft versus host reaction (GvHR) induced in 10-day-old F1 mice by in vitro allogeneically or mitogenically stimulated spleen cells is lower than that induced by unstimulated fresh spleen cells. In vitro stimulated lymphoblasts are unable or only slightly able to induce a GvHR. An active suppression by the blasts is not involved. Since lymphoblasts after in vivo stimulation show an increased ability to elicit a GvHR it is concluded that in vitro and in vivo stimulated lymphoblasts have different properties. A different homing cannot be excluded after transfer to the mouse.