Geographic variation in the humoral response to Pneumocystis carinii

The reported incidence of Pneumocystis carinii pneumonia varies in different areas of the world, but little is known about geographic variation in the antibody response to specific antigens. The frequency of anti-P. carinii antibodies in the serum of normal and human immunodeficiency virus (HIV)-infected individuals from five different regions was compared. Serum specimens from 948 subjects were assayed for IgG antibodies to human-derived P. carinii by Western blot. The overall prevalence of anti-P. carinii antibodies was 72.9%. Among HIV-seronegative individuals, the rate of seropositivity was similar in all regions (70.5%-82.4%). Antibodies to the 30- to 40-kDa antigen were most commonly detected. The frequency of antibodies to high-molecular-mass antigens (95, 120, and > 120 kDa) demonstrated significant geographic variation. This study demonstrates that antibody responses to P. carinii are common in all areas studied but vary in frequency and pattern.