I. DISSOCIATION OF T-CELL ACTIVITIES IN THE MIXED LYMPHOCYTE REACTION AND TWO GRAFT-Vs.-HOST ASSAYS

The graft-vs.-host (GVH) 1 reaction produced in F1 recipients of parental lymphocytes is a complex phenomenon determined by many interacting elements. The antigenic disparity between donor and host (1), the host reaction to attack by donor cells (2), modulating effects of the host on donor cell reactivity (3), and the proportional representation of subpopulations of thymus-derived cells (T cells) in the donor inoculum inducing the reaction (4) are but some of the relevant factors which have been elucidated. An additional component of the reaction has been revealed in the recent studies of Uphoff (reviewed in reference 5). She demonstrated that in lethally irradiated reciprocal hybrid FI mice reconstituted with bone marrow from parental strains, a significant survival advantage was conferred on recipients when the marrow donor strain was syngeneic with the maternal strain of the hybrid cross. I t was suggested that maternal modification in utero of the expression of paternal histocompatibility phenotype on FI cells, resulting in reduced antigenicity, may be responsible for this phenomenon. She also proposed that this effect may serve as a partial explanation for the survival of semiallogeneic fetuses in the uterus of a mother potentially capable of mounting a homograft reaction against fetal histocompatibility antigens of paternal type.