Detecting Pneumocystis carinii by immunohistochemistry

Abstract

Forty-one specimens from patients infected with the human immunodeficiency virus were stained with an anti-Pneumocystis carinii monoclonal antibody. Twenty-eight of the specimens were transbronchial biopsies (TBBx) negative for P carinii by silver stain (SS), and 13 cases were positive for P carinii by SS; 3 of the 13 cases had disseminated disease. Immunohistochemical staining (IHS) revealed P carinii in 3 of the 28 SS-negative TBBx; the finding was limited to a few small clusters of poorly preserved cysts in two cases and was extensive in one case. In the 13 SS-positive cases, IHS staining was strong and delineated the cysts. The number of organisms detected in cases with disseminated disease was strikingly higher than on SS. IHS for P carinii is easier to interpret than SS and visualizes a larger number of organisms. Cost may restrict use to cases in which SS was unable to confirm a physician's strong suspicion of P carinii infection.