Immunotherapy has been used in support of trimethoprim-sulfamethoxazole treatment for Pneumocystis carinii pneumonia. The present study investigated the therapeutic or preventive effects of heterogeneous hyperimmune IgG antibody (HIA) in experimental rats. Their immunity was suppressed by steroid injection, and they were also injected peritoneally with HIA which reacted with 40-55, 92, 116, and 200 kDa bands of the crude antigen. All rats were infected by P. carinii and the cystic forms on lung impression smears were counted. The count was 20.5-76.5 (mean 52.5 + 19.3) in those which received steroid only, but decreased to 6.0-21.0 (mean 13.5 + 10.6) in those of group 3 which received HIA for the same duration. In other groups, the mean count ranged from 29.9 + 32.9 to 54.1 + 47.7, and in those which received 13.7 mg HIA the reduction effect was greater than in those which received 6.8 mg or 20.5 mg HIA. The present finding confirmed that in rats during the early stage of infection, the heterogeneous HIA to MSG antigen bands had a partial effect on P. carinii pneumonia, both prophylactically and therapeutically.
