Major histocompatibility complex gene products on macrophages influence T cell activation

Antigen-pulsed macrophages were used to sensitize or elicit sensitivity from mice of different strains to a variety of antigens. The results indicate that sensitization is directed, not to antigen as such, but to a complex structure on the macrophage surface determined partly by the antigen, and partly by a product coded by the major histocompatibility complex. Delayed type hypersensitivity could be provoked by antigen in responder (R) mice and in the F1 between responder and low responder (LR) strains, but not in LR mice unless pretreated by cyclophosphamide. Sensitivity could be transferred to naive LR-strain mice by lymph node cells taken 5 days after sensitization of cyclophosphamide-pretreated LR mice but not of F1 hybrids between LR and R strains. Sensitivity from these could be transferred only to naive F1 or R-strain mice. The results suggest that low responsiveness cannot be accounted for solely in terms of the operation of a cyclophosphamide-sensitive suppressor mechanism. It is postulated that antigen is less immunogenic when presented by LR-strain cells than by R-strain cells.