Genetic control of cell-mediated immunity in the rat. II. Sharing of either the RT1.A or RT1.B locus is sufficient for transfer of antimicrobial resistance.

The MHC restriction criteria for T cells activating macrophages in vivo and mediating antimicrobial resistance to Listeria monocytogenes were determined. Antimicrobial resistance could be transferred by T cells in order of decreasing efficiency from syngeneic, RT1.A compatible, RT1.B compatible and RT1 incompatible donors. Alloreactive T cells responding to either A locus or B locus encoded antigens in a graft-versus-host reaction were also able to activate macrophages. Approximately five times as many MLC-reactive precursors responded to B locus alloantigens as to A locus alloantigens, but A-restricted Listeria-specific T cells were considerably more numerous (or more efficient) in Listeria-infected hosts than were B-restricted, Listeria-specific T cells. This was unexpected, since A-restricted, Listeria-specific T cells failed to transfer delayed type hypersensitivity (DTH) to soluble bacterial antigens.