HIV-1 induces phenotypic and functional perturbations of B cells in chronically infected individuals

Abstract

A number of perturbations of B cells has been described in the setting of HIV infection; however, most remain poorly understood. To directly address the effect of HIV replication on B cell function, we investigated the capacity of B cells isolated from HIV-infected patients to respond to a variety of stimuli before and after reduction of viremia by effective antiretroviral therapy. B cells taken from patients with high levels of plasma viremia were defective in their proliferative responses to various stimuli. Viremia was also associated with the appearance of a subpopulation of B cells that expressed reduced levels of CD21. After fractionation into CD21(high)- and CD21(low)-expressing B cells, the CD21(low) fraction showed dramatically reduced proliferation in response to B cell stimuli and enhanced secretion of immunoglobulins when compared with the CD21(high) fraction. Electron microscopic analysis of each fraction revealed cells with plasmacytoid features in the CD21(low) B cell population but not in the CD21(high) fraction. These results indicate that HIV viremia induces the appearance of a subset of B cells whose function is impaired and which may be responsible for the hypergammaglobulinemia associated with HIV disease.

Figure 1

Proliferation of B cells relative to plasma viremia. Peripheral blood mononuclear cell-derived B cells were isolated from patients at high viral load, and compared with B cells isolated at low or undetectable viral load and to B cells isolated from a normal HIV-negative donor. Absolute levels of proliferation of B cells isolated from Patient 1 (A) and Patient 3 (B) are indicated, as well as compiled data from all 6 patients expressed as fold enhancement of B cell proliferation at low viral load (VL) over B cell proliferation at high viral load (C). In A and B, data are mean ± SD of triplicates, and in C, data include median fold enhancement for each patient.

Figure 2

Expression of CD21 in B cells. The number of CD21 receptors per CD19⁺ cell (A) and the copy number of CD21 mRNA relative to CD19 mRNA (B) were measured on a group of HIV-infected patients at high plasma viral load (VL), compared with a group of HIV-infected patients at low plasma viral load and a group of normal donors. Means of these data are reported for each group. Median HIV RNA levels in copies per milliliter for each group are shown below the number of patients studied in the respective group. Because of restrictions on the number of cells available, 2 of 9 samples in the high viral load group and 4 of 9 samples in the low viral load group were not subjected to both CD21 mRNA and surface protein measurements.

Figure 3

Properties of CD21-depleted and CD21-enriched B cells of HIV viremic patients. (A) Representative B cells of a chronically viremic patient (Left) were sorted into CD21^low (Center) and CD21^high (Right) fractions. (B) Proliferation of fractionated cells of six patients expressed as fold enhancement of CD21^high B cells over CD21^low B cells, and (C) IgG secretion in 3-day cultures expressed as fold enhancement of CD21^low B cells over CD21^high B cells. Medians of data are reported for B and C.

Figure 4

Electron micrographs showing morphology of normal B cells (A), and B cells of a chronically viremic patient sorted into CD21^high (B) and CD21^low (C) fractions. Original magnifications were ×9,200, ×7,200, and ×5,800 for A, B, and C, respectively.