Immunodepression Associated with Concomitant Toxoplasma and Malarial Infections in Mice

The effects of infections of mice with both Toxoplasma gondii and Plasmodium berghei yoelii were investigated. Mortality, loss of body weight, and spleen size were all greater in the animals infected with T. gondii before P. berghei. yoelii. Malarial parasitemia was more severe and more prolonged, and anemia was greater in the doubly infected animals. Titers of both Sabin-Feldman antibody (Toxoplasma) and fluorescent antibody (malaria) were depressed in the groups infected with T. gondii before P. berghei yoelii. No evidence of protection, i.e., interferon, from either T. gondii or P. berghei yoelii was seen in the doubly infected animals. It is suggested that immunodepression in this situation is due to antigenic competition.