PREFERENTIAL HOMING OF PASSIVELY TRANSFERRED T CELLS INTO SKIN ALLOGRAFTS OF MICE

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Abstract
An assay which uses two differentially labeled cell populations was used to characterize the preferential localization of passively transferred syngeneic cells immunized to specific alloantigens. Splenocytes cytotoxic to B10.D2 and B10.BR alloantigens were harvested from (C57BL/6 × A/J)F1 (B6AF1) donors bearing acutely rejected skin allografts. One population was labeled in vitro with 3H-thymidine and the other with 14C-thymidine. The labeled cells were pooled and then transferred i.v. into B6AF1 hosts bearing 5-day-old skin grafts from B10.D2 and B10.BR donors. After 48 hr the mice were killed, and the relative amount of cells present in the skin grafts and draining axillary lymph nodes was derived by comparing the 3H:14C ratios of the harvested tissues. The results of these studies indicated that cytotoxic splenocytes harvested from donors bearing acutely rejected skin allografts preferentially localize to the relevant skin allograft after passive systemic transfer. The homing behavior of these splenocytes was augmented by T cell enrichment and significantly diminished by pretreatment with anti-Thy-1.2 serum plus rabbit complement. There was no evidence of preferential homing within the draining axillary lymph nodes. It can be concluded that a T cell population derived from in vivo sensitized splenocytes exhibits preferential homing to relevant skin allografts upon passive transfer. There is evidence that tissue allograft destruction is mediated primarily by cellular immune mechanisms (1–3). Previous reports have indicated that the cellular infiltration of such acutely rejected allografts is heterogeneous and that an early event leading to acute rejection is the infiltration of cytotoxic T cells (4–6). The distribution of lymphocytes after transfer into a syngeneic host displays patterns of homing determined by properties inherent to the transferred cell population and previous antigenic exposure of the host (7–10). Billingham and Medawar (2) have shown that accelerated primary skin graft rejection can be accomplished with the passive systemic transfer of sensitized lymphoid cells. It has been postulated that these cells initiate accelerated graft rejection by specific migration into the graft that expresses the target alloantigen. Early investigations failed to demonstrate preferential homing to relevant skin allografts of transferred effector cells (11–13). These findings were consistent with a random allocation of effector cells to skin allografts. More recently, several reports have documented small but significant preferential homing of sensitized lymphoid cells to skin allografts (14–16). This study examines whether or not cytotoxic cells localize specifically to skin allografts in a murine model. Our findings indicate that preferential homing was demonstrable using in vivo sensitized splenocytes and was a T cell phenomenon.