Detection of the 70-kilodalton Histoplasma capsulatum antigen in serum of histoplasmosis patients: Correlation between antigenemia and therapy duringfollow-up

Histoplasmosis is an important systemic fungal infection, particularly amon g immunocompromised individuals, who may develop a progressive disseminated form which is often fatal if it is untreated. In such patients, the detect ion of antibody responses for both diagnosis and follow-up may be of limite d use, whereas the detection of Histoplasma capsulatum var, capsulatum anti gens may provide a more practical approach. We have recently described an i nhibition enzyme-linked immunosorbent assay (ELISA) for the detection in pa tients' sera of a 69- to 70-kDa H. capsulatum var, capsulatum-specific anti gen which appears to be useful in diagnosis. To investigate its potential f or the follow-up of histoplasmosis patients during treatment, antigen titer s in the sera of 16 patients presenting with different clinical forms of hi stoplasmosis were monitored at regular intervals for up to 80 weeks. Sera f rom four of five patients with the acute form of the disease showed rapid f alls in antigenemia, becoming antigen negative by week 14 (range, weeks 10 to 16). Sera from four patients with disseminated histoplasmosis showed fal ls in antigen levels; three of them became antigen negative by week 32; the fourth patient became negative by week 48. In contrast, antigen titers in four of six AIDS patients with the disseminated form of the disease remaine d positive throughout follow-up. Sera from only one patient who presented w ith the chronic form of the disease were analyzed, and this individual's se rum became antigen negative by week 9. The inhibition ELISA is shown to be of particular use in the monitoring of non-AIDS patients with the acute and disseminated forms of the disease and may complement existing means of fol low-up.