Quantitation of Anti–Pneumocystis jiroveciAntibodies in Healthy Persons and Immunocompromised Patients

To facilitate studies of the epidemiology of Pneumocystis jiroveci infection in both healthy persons and immunocompromised patients, we developed a quantitative ELISA with recombinant major surface glycoprotein (MSG) fragment MSG-14, a P. jiroveci-specific protein that includes a highly conserved region of the MSG protein family. By immunoblot, all samples reacted with the carboxyl portion of MSG-14; by ELISA, immunocompromised patients with Pneumocystis pneumonia (PCP) who were immunocompromised for reasons other than AIDS had higher antibody levels than did either patients with AIDS with PCP (P=.01) or healthy persons (P=.005). Longitudinal observations of 8 patients with AIDS showed no correlation between time of diagnosis of Pneumocystis infection and change in antibody levels. Eleven percent (4/35) of healthy persons demonstrated a >4-fold change in antibody titers during 1 year of observation. This ELISA assay allows quantitation of anti-P. jiroveci antibodies in human serum samples and should be useful in better understanding the epidemiology of P. jiroveci infection in humans.