Identification of a CD21 receptor-deficient, non-Ig-secreting peripheral B lymphocyte subset in HIV-seropositive drug abusers.

We have studied 61 HIV-seropositive heroin addicts (18 asymptomatic, 20 ARC, and 23 AIDS cases), 26 HIV-seronegative heroin addicts, and 45 healthy blood donors, matching the groups each other for age and sex. We have focused on the phenotypic characteristics of B subpopulations in the peripheral blood of HIV-seropositive and -seronegative drug abusers, paying particular attention to the consistence of the "CD20+" B cell subset, which poorly expresses the CD21 membrane receptor for the C3d and Epstein-Barr virus (EBV) (referred to as "CD20 + CD21-" subset). In healthy blood donors, the ratio CD20 + CD21-/CD20+ x 100 is extremely low (mean +/- SEM = 8.1 +/- 0.9) and rarely exceeds the value of 20. On the contrary, in HIV seropositives, the values are much more dispersed, with higher mean values (mean +/- SEM = 25.8 +/- 1.8) ranging from 50 to 60. An intermediate situation characterizes the class of HIV-seronegative heroin addicts, whose values are slightly higher and more dispersed than that of normal controls (mean +/- SEM = 11.6 +/- 1.3). The extent of the amplification of the CD20 + CD21- subset in HIV-seropositive individuals does not apparently correlate with the progression of the disease and represents an early event in the clinical course of HIV infection. For each subject of the study group, the number of CD20 + CD21- B lymphocytes is not correlated to other early markers of HIV infection, as the T4 lymphocyte number, or total Ig levels in sera. A functional characterization of the CD20 + CD21- B cell subset indicates that, in HIV-seropositive patients, these cells are unable to produce specific and nonspecific immunoglobulins (Ig's), either spontaneously or after pokeweed mitogen stimulation. Furthermore, this cell subset is characterized by poor expression of surface Ig's. The data reported suggest that this cell subset can be regarded as situated at an early level of B cell lineage differentiation.