The Stimulus to Host Cell Proliferation in Graft‐versus‐Host Reactions

Abstract

Two experiments are described concerned with the mechanism of host cell activation in the rat popliteal lymph node (LN) undergoing a graft-vs.-host (GVH) reaction. Irradiated, F1 hybrid hosts (750 rad) mounted an impaired response to parental strain T cells. This was augmented by an i.v. injection of F1 hybrid lymphocytes but not by parental strain B lymphocytes syngeneic with the initiating T cells. When the donor T cells (footpad) and B lymphocytes (i.v.) were completely allogeneic the residual response of the irradiated F1 was completely inhibited. The popliteal LN response in the semi-allogeneic situation of the type (A .times. C)F1 .fwdarw. (B .times. C)F1 was, if anything, weaker than in the allogeneic situation AA .fwdarw. BB. These results and other data are discussed in terms of a possible major histocompatibility complex (MHC) requirement for host cell activation. The sharing of an MHC haplotype between donor and host cells is unlikely to be a necessary or sufficient condition for host cell activation.