Detection of human immunodeficiency virus (HIV) in serum and body fluids by sequential competition ELISA

A micro-ELISA based on competition with the biotin-labeled 25 kDa gag (p25gag) recombinant protein of the human immunodeficiency virus (HIV) was compared to commercial antigen capture ELISAs for the detection of viral antigens in a variety of body fluids including serum, cerebro-spinal fluid (CSF), sputum, saliva, milk, semen, vaginal and bronchial fluids, as well as earwash fluid. Two-thirds (24/30) of these specimens contained IgG and/or IgA antibodies to HIV. The results were correlated with the recovery of infectious HIV in culture. The competition ELISA detected the presence of HIV antigen in 4 out of 8 sera, 5 out of 6 CSF and 6 out of 15 other body fluids that were found to contain infectious virus. Comparatively, 5 of the 8 sera, 3 of the 6 CSF, and 2 of the 15 body fluids tested positive for HIV antigen by capture ELISA. The data suggest that the competition test is more effective than the capture method in detecting antigen in CSF and body secretions, which might be due to the presence of immune complexes. However, both ELISA methods showed similar susceptibility to antibody interference in spiked specimens. The results confirm that antigenemia status can be of value in assessing HIV infection when used in combination with other clinical and laboratory data.