Background. Examination of the in vivo activation and function of CD4+ T cells in response to allografts may advance our understanding of the rejection process. We analyzed the capacity of transgenic class IIrestricted CD4 T cells to reject skin, cardiac, and islet transplants. Methods. TS1 mice possess a high frequency of CD4+ T cells specific for the immunodominant epitope of the viral hemagglutinin (HA) protein. We analyzed the kinetics of rejection of skin, heart, and islet grafts by naïve and sensitized TS1 mice and by adoptively transferred TS1 lymphocytes. Results. Rejection of heart transplants was more rapid than skin grafts (mean survival time, 12.9 vs. 26.6 days), and islet grafts survived indefinitely in TS1 mice. These findings may be partly attributable to the supranormal frequency of HA-reactive cells in TS1 mice. In support of this, we found that adoptive transfer of 5 × 105 TS1 lymphocytes to Balb/c hosts effected consistent rejection of HA-bearing skin transplants, whereas a significantly greater number (3 × 106) was required for heart transplant rejection. The in vivo proliferative response of HA-specific T cells to heart and skin was found to be robust and predominantly localized to the draining lymph nodes. Conclusion. We developed a model of allograft rejection in which the responding T cells and relevant graft antigen are specifically defined. Adoptive transfer of carboxy-fluorescein succinimidyl ester-labeled transgenic T cells allowed us to visualize a robust proliferative response in vivo to heart and skin allografts, which in both cases was localized to regional lymph nodes.
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