Surfactant protein-A levels increase during Pneumocystis carinii pneumonia in the rat

In bronchoalveolar lavage (BAL) of human immunodeficiency virus (HIV)-infected patients with Pneumocystis carinii pneumonia and in lungs of glucocorticoid-immunosuppressed rats infected with P. carinii, surfactant phospholipid levels are reduced. However, levels of the surfactant-associated protein-A (SP-A) in BAL are 4-5 times higher than normal in patients with P. carinii pneumonia. In this study, we examined the effects of glucocorticoid immunosuppression and P. carinii infection on SP-A messenger ribonucleic acid (mRNA) and protein levels in rat lungs. Rats were immunosuppressed by adding dexamethasone to their drinking water and were infected with P. carinii by intratracheal instillation of the organism. SP-A was measured by enzyme-linked immunosorbent assay (ELISA) and SP-A mRNA by hybridization of Northern blots with an SP-A complementary deoxyribonucleic acid (cDNA) probe. There was a severalfold increase in SP-A protein and mRNA levels in uninfected glucocorticoid-treated rats. However, contrary to what has been reported with the surfactant-associated lipids, SP-A mRNA and protein levels in P. carinii-infected animals were significantly higher than those found in the uninfected, immunosuppressed animals. Our results demonstrate that SP-A increases, probably as a result of elevated mRNA levels, in immunosuppressed rats with P. carinii infection and are consistent with our findings in HIV-positive patients with P. carinii pneumonia.