Recent developments in the serodiagnosis of histoplasmosis

Histoplasmosis is an important systemic fungal infection, with worldwide distribution, although it is more common in temperate and tropical climates. Its accurate diagnosis requires fungal isolation or the visualization of yeast in tissues or in biological samples. However, serological tests may play an important role in the rapid diagnosis of disease either by antibody or antigen detection. Immunodiffusion/complement fixation are the most widely tests used for the detection of antibody responses but cross-reactivity has been a traditional problem. However, recently several recombinant proteins have been produced but their application in serodiagnosis awaits investigation. For immunocompromised patients, the detection of antibody responses for both diagnosis and follow-up may be of limited use, whereas the detection o f H . ca p su la tu m antigen may be more effective. A radioimmunoassay (RIA) test for antigen detection in sera and urine is currently available although this suffers problems from cross-reactivity. More recently, using a monoclonal antibody (MoAb) which is directed against a 70 kDa antigen, an inhibition ELISA (inh-ELISA) for the detection of circulating antigen has been developed. This inh-ELISA is of particular use in monitoring non-AIDS patients with the acute/disseminated forms of histoplasmosis, and complements existing forms of followup.