- S Karpatkin: Department of Medicine, New York University Medical Center, NY 10016.
Anti-CD4 antibody was found in 30% of human immunodeficiency virus (HIV-1)-seropositive thrombocytopenic patients compared with 5% of nonthrombocytopenic seropositive patients (chi 2 = 21.7, P less than 0.001) and was shown by the following observations to contain internal-image anti-idiotype antibody (Ab2) directed against the antibody (Ab1) to gp120, the HIV-1 envelope glycoprotein that binds to CD4: (i) affinity-purified anti-CD4 (Ab2) bound to affinity-purified anti-HIV-1gp120 (Ab1) on solid-phase radioimmunoassay, and binding could be blocked by recombinant CD4 (rCD4) as well as recombinant gp120 (rgp120); (ii) F(ab')2 fragments of Ab1 inhibited the binding of Ab2 to rCD4; (iii) Ab2 inhibited the binding of Ab1 to HIV-1 beads; (iv) Ab2 inhibited the binding of Ab1 to gp120 on immunoblot; (v) Ab2 bound to the CD4 receptor on a CD4-bearing T-cell line, H9; (vi) Ab3 (anti-rgp120) could be produced in vivo by immunizing mice with Ab2, and binding of Ab3 to rgp120 could be blocked with rCD4; and (vii) three different Ab2 preparations bound to two different homologous Ab1 preparations. Ab1 or Ab2 alone did not bind to platelets, whereas the idiotype-anti-idiotype complex did bind to platelets in a concentration-dependent manner. Binding of the internal-image complex was 10-fold greater than that of a non-internal-image Ab1-Ab2 complex composed of anti-HIV-1gp120 and anti-anti-HIV-1gp120. Thus, patients with HIV-1 thrombocytopenia contain internal-image idiotype-anti-idiotype complexes that could be affecting CD4 cell number or function, inhibiting HIV-1 binding to CD4 cells or contributing to HIV-1 thrombocytopenia.