Humoral immunity in experimental Pneumocystis carinii infection. I. Serum and bronchial lavage fluid antibody responses in rats.

Humoral immune responses to Pneumocystis carinii were studied in rats by an IFA technique. Serum IgG antibody titers to the organism were diminished in rats administered corticosteroids to produce P. carinii infection but rose with steroid tapering and clearance of the organism from the lungs. A similar pattern of changes occurred in total serum IgG and IgM but not IgA levels by single radial diffusion. Serum antibody titers developed in control rats housed in the same room for greater than or equal to 10 weeks with P. carinii--infected rats and in old but not young rats obtained from commercial breeders. Antibody titers in bronchial lavage fluid supernatants paralleled those in serum, but albumin levels were low and IgA was the only immunoglobulin detected. By contrast, P. carinii organisms in lavage fluid sediments had IgG, IgA, and IgM detected by IFA on their surface. We conclude that the host develops systemic and local antibodies to P. carinii with both active infection and prolonged environmental exposure.