Abstract: AIM: To assess the diagnostic value of Pneumocystis carinii(PC) antibodies and
circulating antigens detection in alveolar lavage fluid(ALF) and serum. METHODS: The
immunosuppressive rat model was used in this study. The PC antigens in both ALF and sera were
detected by double sandwich ELISA, and the specific IgG antibody levels in sera were detected by
IFA at different times after immunosuppression treatment. The detection results were compared
with the corresponding results of PC finding in lung impression smear. RESULTS: The PC antigens in ALF were positive in all infected rats 6-8 weeks after immunosuppression while in control rats were all negative. By comparison, the PC antigens detected from sera were negative in most infected rats. During immunosuppression treatment with steroid, antibody titers in the infected rats rose slightly in some rats. After steroid was withdrawn, PC antigens in ALF became negative gradually but antibody teters rose progressively with time in all rats. CONCLUSION: Detecting PC antigens in ALF may be useful for diagnosing PC infection but these antigens were difficult to be detected in serum. The rise in serum IgG antibody does not necessarily indicate an existing infection.

Key words: Pneumocystis carinii, immunological diagnosis, ELISA, IFA, rat model