Serum antibody response to active infection with Cryptococcus neoformans and its varieties in immunocompetent subjects.

Using a class-specific enzyme immunoassay IgG and IgA anticryptococcal antibody was measured in 400 serum specimens at 1 week to 11.7 years after diagnosis from 43 immunocompetent subjects with confirmed active cryptococcosis. The prevalence of IgG was 86% at diagnosis, rose to 100% by 2 weeks and remained high thereafter. IgA prevalence was 71% at diagnosis, rose to 75% at 2 weeks and then fell over 2 years. IgG and IgA prevalence in paediatric controls was 5% and 0%, respectively. Mean antibody levels showed the same pattern and neither levels nor prevalence were influenced by age, sex or site of infection. Patients with the variety gattii infection had a greater antibody response than those with the variety neoformans which was significant for IgA. Specific anticryptococcal antibody was regularly present in conjunction with cryptococcal antigen at diagnosis. IgG persists but IgA falls over 1-2 years. The assay described may be a useful tool to study the antibody response and seroepidemiology of infection with C. neoformans.