Immunohistochemistry of Pneumocystis carinii

The recent explosion in the acquired immune deficiency syndrome epidemic brought about an increased need for specific markers that recognize Pneumocystis carinii. Newly developed antibodies mark cyst and/or trophozoites, but have not been thoroughly characterized. While the sensitivity of the immunocytochemical method appears greater than that offered by the Giemsa strain, it is only slightly better than that of GMS stain. That slight edge in sensitivity warrants the use of immunostaining in specimens such as sputum, where identification of Pneumocystis carinii as the sole pathogen is more difficult than in bronchoalveolar lavage. In the latter specimen, we still recommend rapidly performed GMS with the microwave technique because of its utility in recognizing fungi. With refinements in the antibodies available, immunostaining may offer further advantages in patient management.