Stimulation of rat graft-versus-host reactions by polyinosinic-polycytidylic acid.

The effect of polyinosinic-polycytidylic acid (poly I:C) treatment on the rat graft-versus-host reaction (GVHR) initiated in parental to F1 hybrid strain combinations differing at either major or minor histocompatibility determinants were studied in three different protocols. 1 A GVHR initiated in juvenile (LBN)F1 recipients and treated concurrently with poly I:C alone produced neither splenomegaly nor dermatitis in these juvenile rats. (2) Pretreatment of L donors with a single injection of poly I:C 3 days before initiation of the GVHR enhanced resultant splenomegaly in the newborn (LBN)F1 recipients. A high poly I:C dose was inhibitory. (3) Newborn recipients which received lymphocytes from L donors and which were concurrently treated with poly I:C developed dermatitis at an accelerated rate. However, poly I:C alone given to newborns mimicked the GVHR by induction of a syndrome characterized by splenomegaly, dermatitis, thymic involution, and body growth retardation. The parental L and (LF)F1 hybrid strain combination differing only at a minor histocompatibility determinant or in an isogenic hybrid combination (LBN)F1 leads to (LBN)F(1) developed no GVHR when recipients were treated with poly I:C. We conclude that poly I:C can stimulate a rat GVHR initiated with unsensitized donor cells differing at a major histocompatibility locus.