Reduced concentrations of IgG antibodies to Pneumocystis carinii in HIV-infected patients during active Pneumocystis carinii infection and the possibility of passive immunisation.

The relationship between Pneumocystis carinii antibody concentrations and acute Pneumocystis infection was investigated by testing sequential samples of serum from HIV antibody-positive patients with respiratory symptoms and HIV-negative immunocompromised patients by means of an indirect immunofluorescence assay for specific IgG antibodies to P. carinii. Loss of circulating antibody at the time of active Pneumocystis infection was observed in five patients with proven infection. Three others showed recovery of antibody coinciding with treatment and clinical recovery from infection. Concentrations of specific IgG antibody against P. carinii were measured in 40 blood donors and in six different batches of an intravenous immunoglobulin (IV Ig) preparation. Titres greater than 128 were found in the IV Ig batches examined. The use of IV Ig, either alone or in conjunction with other therapeutic agents, should therefore be considered in patients suffering from acute infection with P. carinii.