A study of cellular and humoral immune responses in owl monkeys (Aotus trivirgatus) following vaccination against Plasmodium falciparum.

VACCINATION OF ANIMALS AGAINST MALARIA PARASITES IS THOUGHT TO INDUCE TWO BASIC IMMUNOLOGICAL RESPONSES: (i) specific recognition of parasite antigens by the host, and (ii) a generalized immune enhancement due to the presence of adjuvant. Immunological techniques were used in this study to monitor cellular and humoral immune changes in owl monkeys prior to and following immunization with a vaccine consisting of merozoite-enriched schizonts of Plasmodium falciparum and one of three adjuvants: N-acetylmuramyl-L-alanyl-D-isoglutamine (muramyl dipeptide), Freund's complete adjuvant, or 6-O-stearoyl-N-acetylmuramyl-L-alanyl-D-isoglutamine. The results showed that most of the immunized animals responded specifically to malarial antigens as demonstrated by the fact that peripheral blood lymphocytes underwent blast transformation in vitro in the presence of parasite antigens and that substantial antibody titres were produced as detected by indirect immunofluorescence. By use of the in vitro inhibition test, it was found that sera from immunized owl monkeys collected after challenge greatly inhibited merozoite reinvasion. Generalized nonspecific immune responses observed in owl monkeys following vaccination included an increase in the number of white blood cells and the proportion of T and B cells in the peripheral blood. Responses to mitogen stimulation with phytohaemagglutinin, concanavalin A, and pokeweed mitogen, however, did not appear to be appreciably affected by immunization.