2-SITE ENZYME-IMMUNOASSAY OF CD4 AND CD8 MOLECULES ON THE SURFACE OF T-LYMPHOCYTES FROM HEALTHY-SUBJECTS AND HIV-1-INFECTED PATIENTS

A highly sensitive two-site enzyme immunoassay (Capcellia(R)) was deve loped to determine the concentration of CD4 and CD8 molecules expresse d on the surface of human T lymphocytes. This assay, performed in one step (20 min), involves the specific immunocapture of T lymphocytes an d reaction of the CD4 or CD8 molecules with an enzyme-labeled monoclon al antibody (mAb). The results were expressed as molar concentrations of the T-cell markers on the basis of results obtained with calibrated CD4 and CD8 standards. The assay was sensitive enough to detect 0.4 p mol/L CD4 or 0.8 pmol/L CD8, which corresponded to similar to 20 x 10( 6) CD4(+) or CD8(+) T cells per liter of blood. Mean concentrations in healthy adults were 17.2 pmol/L for CD4 and 22.1 pmol/L for CD8. The CD4 concentration was <8 pmol/L in 50% of HIV-1-infected patients and in 95% of AIDS patients. Given the epitopic specificity of the mAb to CD4 we used, these values correspond to the concentration of CD4 molec ules free of envelope glycoprotein (gp)120.