Detection of delayed hypersensitivity in mice injected with ribonucleic acid-protein fractions of Salmonella typhimurium.

Manifestations of delayed hypersensitivity (cell-mediated immunity) were found to be present in mice immunized with virulent Salmonella typhimurium SR-11 subfractions which contained appreciable concentrations of bacterial protein and in mice immunized with the living, attenuated RIA strain of S. typhimurium. Delayed hypersensitive responses were measured by footpad sensitivity in the immunized mice and in vitro by inhibition of spleen cell migration and by increase in (3)H-thymidine uptake by lymphoid cell populations when exposed to bacterial fractions rich in protein content.