Decreased expression of the C3b/C4b complement receptor (CR1) in AIDS and AIDS-related syndromes correlates with clinical subpopulations of patients with HIV infection.

Expression of the C3b/C4b receptor (CR1) was studied on erythrocytes of 153 individuals infected with HIV and 104 age-matched normal individuals by measuring the uptake of 125I-labelled monoclonal anti-CR1 antibody. The mean number of CR1 sites on erythrocytes of asymptomatic seropositive individuals (822 +/- 270; mean +/- s.d.) and of patients with persistent generalized lymphadenopathy (PGL; 775 +/- 320) did not differ significantly from that of normal subjects. The number was significantly lower in patients with AIDS-related complex (ARC; 543 +/- 233; P less than 5 x 10(-3)) and further decreased in patients with AIDS (442 +/- 271; P less than 1 x 10(-4)), whether they presented with Kaposi's sarcoma (KS) or opportunistic infections. An additional finding was that of decreased expression of antigenic and functional CR1 in neutrophils from patients with AIDS, as assessed by radioimmunoassay of CR1 in detergent-solubilized cells and the capacity of intact cells to form rosettes with C3b-coated erythrocytes. Low numbers of CR1 on cells from patients with AIDS were not due to occupation of the receptor by C3 fragments on immune complexes. The correlation that was observed between decreased numbers of CR1 on erythrocytes and clinical subpopulations of symptomatic HIV-infected patients suggests that CR1 expression on erythrocytes may represent a valuable marker of the severity and natural history of HIV-associated disease.