Effects of Surfactant Protein-A on the Interaction of Pneumocystis murina with its Host at Different Stages of the Infection in Mice

ABSTRACT. We examined the effects of surfactant protein A (SP-A), a collectin, on the interaction of Pneumocystis murina with its host at the beginning, early to middle, and late stages of infection. Pneumocystis murina from SP-A wild-type (WT) mice inoculated intractracheally into WT mice (WT_S-WT_R) adhered well to alveolar macrophages, whereas organisms from SP-A knockout (KO) mice inoculated into KO mice (KO_S-KO_R) did not. Substitution of WT mice as the source of organisms (WT_S-KO_R) or recipient host macrophages (KO_S-WT_R) restored adherence to that found with WT_S-WT_R mice. In contrast, when immunosuppressed KO and WT mice were inoculated with P. murina from a homologous source (KO_S-KO_R, WT_S-WT_R) or heterologous source (WT_S-KO_R, KO_S-WT_R) and followed sequentially, WT_S-KO_R mice had the highest levels of infection at weeks 3 and 4; these mice also had the highest levels of the chemokine macrophage inflammatory protein-2 and neutrophils in lavage fluid at week 3. Surfactant protein-A administered to immunosuppressed KO_S-KO_R mice with Pneumocystis pneumonia for 8 wk as a therapeutic agent failed to lower the organism burden. We conclude that SP-A can correct the host immune defect in the beginning of P. murina infection, but not in the middle or late stages of the infection.