Host defenses in murine malaria: nonspecific resistance to Plasmodium berghei generated in response to Mycobacterium bovis infection or Corynebacterium parvum stimulation.

Infection with Mycobacterium bovis (BCG) or injection of killed Corynebacterium parvum protected some strain B6D2 F1 (C57BL/6xDBA/2) mice but did not protect strain ICR or A mice from lethal challenge with Plasmodium berghei strain NYU-2. B6D2 mice were not protected against challenges delivered immediately after intravenous injection of these materials, but rather protection developed by day 7 and persisted through at least day 84. Infections in protected mice progressed to about 10% parasitemia in parallel with infections initiated with the same inoculum in untreated controls. However, infections in most of the protected mice were cleared subsequently, whereas infections in untreated controls were uniformly fatal. A small number of treated mice developed protracted high-level erythrocytic infections, which led to markedly delayed death. BCG-infected mice which survived P. berghei infections had a factor in their sera which protected passively immunized recipients from P. berghei. BCG-infected mice passively immunized with protective serum controlled P. berghei infections better than normal mice given the same amount of the same serum and challenged with the same P. berghei inoculum. The capacity of BCG-infected B6D2 mice to resist P. berghei infection was not directly related to the pattern of growth of BCG, to the degree of splenomegaly, or to the level of activation of macrophages (measured as microbicidal capacity) caused by BCG infection. Therefore, I concluded that (i) BCG infection or injection of killed C. parvum altered the immunological potential of B6D2 mice in such a way as to allow the production of measurable levels of a protective humoral factor in response to infection with P. berghei; (ii) BCG infection caused the generation of a capacity which, when expressed in the presence of immune serum, provided an anti-P. berghei capacity which was superior to that provided by BCG infection alone or immune serum in the absence of BCG infection; and (iii) not all strains of mice could be protected from P. berghei by BCG or C. parvum injection.