Blocking-ELISA for detection of specific antibodies to the glycoproteins of the human immunodeficiency virus type 1 (HIV-1)

A blocking ELISA was developed to confirm the specificity of screening tests for anti‐HIV‐1 antibodies. A murine monoclonal antibody (McAb) raised against recombinant gp 160 was used in combination with a commercial technique (ELAVIA‐1). After determining the optimal experimental conditions, the assay was applied to 92 samples presenting different reactivities by Western blot (WB) analysis. All the sera containing antibodies to gp160/gp120 (53) were positive in our assay. The six patients who sero converted showed a low positivity by ELAVIA‐1 (optical density near the cutoff value) reacted by blocking‐ELAVIA‐1 with an McAb binding inhibition greater than 85%. By contrast, negative samples (29) and specimens that exhibited reactivity only against gag‐proteins (10) were not detected (McAb binding inhibition smaller than 15%). This sensitive and specific blocking‐ELAVIA‐1 represents a convenient alternative to WB as a confirmatory test. The technique is time‐saving and inexpensive and can easily be integrated with a screening test for diagnostic or epidemiologic studies on HIV‐1 infection.