Continuous expression of I-A antigen by peritoneal macrophages from mice resistant to Mycobacterium bovis (strain BCG).

Monoclonal antibodies were used to monitor the expression of I-A antigen on the surface of macrophages obtained from mice immunized to Mycobacterium bovis (strain BCG). Unlike the transient nature of I-A expression by macrophages from Listeria-injected mice, peritoneal macrophages from mice injected 28 days previously with 10(4) BCG expressed I-A continuously. The continued expression was not due to the presence of antigen or of contaminating lymphocytes. When we compared the kinetics of I-A expression from different strains of mice, the continuous expression of I-A correlated with the genetic resistance of the mice to BCG. Macrophages from mice that were resistant to BCG expressed I-A continuously, while macrophages from BCG susceptible mice expressed I-A transiently. Injection of resistant mice with Salmonella typhimurium did not result in the induction of a population of macrophages that expressed I-A continuously. This suggests that the Bcg gene may not be the same as that responsible for resistance to Salmonella (Ity) or Leishmania (Lsh).