Allogeneic restriction of acquired antimicrobial resistance in the rat.

Allogeneic restriction of acquired antimicrobial resistance was demonstrated by infusing Listeria-immune thoracic duct lymphocytes (TDL) into syngeneic, semisyngeneic, or allogeneic recipients that had been infected i.v. with Listeria monocytogenes (LM). Syngeneic and semisyngeneic recipients enjoyed a high level of protection (3 to 5 log10 reduction in viable organisms within 64 hr, whereas allogeneic recipients were poorly protected (0.5 to 2.5 log10 reduction). Sharing one haplotype between TDL-donors and challenged recipients resulted in a 4- to 8-fold increase in the level of resistance transferred. Histoincompatibility reactions could be excluded as a cause of the observed allogeneic restriction. Therefore, it is likely that LM-immune TDL are unable to respond efficiently to the antigens of this organism in an allogeneic environment. But allogeneic immune TDL do confer a low level of protection that cannot be ascribed to B cell activity nor to GvH and/or HvG reactions. Evidence is provided that the modest protection afforded by allogeneic lymphocytes is conveyed by the same T cell subset that operates with much higher efficiency in genetically related rats.