Immunosuppressed surfactant protein A-deficient mice have increased susceptibility to Pneumocystis carinii infection

Immunosuppressed Swiss Black mice deficient in surfactant protein A (SP-A(- /-)) and wild-type control mice (SP-A(+/+)) were exposed to Pneumocystis ca rinii by environmental exposure, intratracheal inoculation, and direct expo sure to other infected animals. The frequency and intensity of P. carinii i nfection were significantly greater in the SP-A(-/-) mice by all 3 methods of exposure. P. carinii free of SP-A and alveolar macrophages were isolated from SP-A(-/-) mice and were tested in an in vitro attachment assay. Pretr eatment of P. carinii with human SP-A resulted in a significant dose-depend ent increase of the adherence of P. carinii to the macrophages. Thus, SP-A plays a role in host defense against P. carinii in vivo, perhaps by functio ning as a nonimmune opsonin.