In vitro secondary mixed leukocyte reaction (MLR). II. Interaction MLR determinants expressed by F1 cells.

T cells from strain A primed in vitro to (C57BL/6 x A/JF1 [(B6 x A)F1] cells respond better to restimulation by (B6 x A)F1 than by B6 or a 1:1 mixture of A and B6 cells. The increase in the response to F1 cells is specific and due to MLR determinants present on (B6 x A)F1 cells but not on either of the parental cell types. (B6 x A)F1 cells express more than one F1-specific MLR determinant, and this expression is dependent upon products of alleles of at least two loci within the major histocompatibility complex (MHC). Responsiveness to these F1-MLR determinants is apparently controlled by more than one locus within the MHC.