In vitro secondary mixed leukocyte reaction (MLR)

T cells from strain A primed in vitro to (C57BL/6 × A/J)F1 [(B6 × A)F1 ] cells, respond better to restimulation by (B6 × 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 × A)F1 cells but not on either of the parental cell types. (B6 × 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.