Background:  In previous studies we identified perturbations in B cells of HIV-viremic patients that were consistent with activation-induced terminal differentiation, including loss of CD21 expression in association with decreased proliferation, increased immunoglobulin secretion, and appearance of plasma cell-like morphologies. Here, we performed DNA microarray and phenotypic and functional analyses in an effort to clarify the mechanisms of B-cell perturbation associated with ongoing HIV replication in infected individuals.

Methods:  B cells isolated from HIV-viremic patients were compared with B cells of HIV-aviremic and HIV-negative patients by analyzing gene expression profiles, phenotypic profiles of B cell surface markers, and functional profiles associated with B-cell survival and stimulatory pathways.

Results:  More than 40 genes were found to be upregulated in B cells of HIV-viremic patients when compared with B cells of HIV-aviremic and HIV-negative patients. Several of these genes were associated with B-cell terminal differentiation, including CD38, CD95, CXCR3, and BCMA. FACS analysis confirmed these increases at the protein level and indicated that most of the up-regulated genes were seen in the CD21low subpopulation, shown to be abundant in B cells of HIV-viremic patients.  Furthermore, the increased expression of 2 members of the TNF superfamily of receptors, namely CD95 (Fas) and BCMA (1 of 3 receptors for BLys), were associated with increased B-cell apoptosis following incubation with Fas ligand and reduced responsiveness to Blys, respectively, with CD21low B cells accounting for the increases in cell death and decreases in B-cell proliferation.

Conclusions:  Our data demonstrate that ongoing HIV replication leads to profound B-cell dysfunction due to aberrant induction of terminal differentiation. Most noteworthy was the increased expression of the  TNF superfamily receptors that correlated with increased susceptibility of B cells to TNF superfamily ligand-mediated cell death. These data are consistent with our previously reported studies that HIV-induced hyperactivity leads to the appearance of plasmacytoid cells that are ineffective at responding to antigenic stimulation and interacting with cognate CD4⁺ T cells.

Keywords: B cells; apoptosis; activation markers