Blocking effect of rheumatoid factor and cold agglutinins on complement fixation tests for histoplasmosis.

The blocking effect of rheumatoid factor (RF) and cold agglutinins (CA) on the detection of complement-fixing (CF) antibodies for Histoplasma capsulatum using a mycelial (histoplasmin) and a yeast antigen was studied. Sera from 213 patients serologically positive for histoplasmosis were screened for the presence of RF or CA. CF antibodies to H. capsulatum in sera containing RF or CA were studied before and after removal of these factors (RF and CA) by treatment with dithiothreitol. Results suggest that RF or CA may interfere with the CF reaction to the yeast antigen of H. capsulatum but not to the mycelial antigen (histoplasmin).