Immune activation and increased IL-21R expression are associated with the loss of memory B cells during HIV-1...

Microbial translocation and chronic immune activation were previously shown to be associated with impairment of T cell functions and disease progression during infection with human immunodeficiency virus type-1 (HIV-1); however, their impact on B cell function and number remains unknown. By measuring markers of immune activation and molecules involved in apoptosis regulation, we have evaluated the association between microbial translocation and loss of memory B cells in HIV-1-infected patients.

Markers of activation [the interleukin-21 receptor (IL-21R) and CD38] and apoptosis (Bim, Bcl-2 and annexin V) were measured in B cell subpopulations by multicolour flow cytometry. Levels of soluble CD14 (sCD14) and lipopolysaccharide (LPS), measures of microbial translocation, were determined in plasma. Purified B cells were also exposed in vitro to Toll-like receptor (TLR) ligands.

IL-21R expression was higher in cells from HIV-1-infected patients, compared with control subjects, with the highest levels in nontreated patients. An inverse correlation was observed between IL-21R expression and percentages of circulating resting memory (RM) B cells. IL-21R-positive memory B cells were also more susceptible to spontaneous apoptosis and displayed lower levels of Bcl-2. It is interesting that the levels of sCD14, which are increased during HIV-1 infection, were correlated with decreased percentages of RM B cells and high IL-21R expression. In the plasma of HIV-1-infected individuals, a correlation was found between sCD14 and LPS levels. TLR activation of B cells in vitro resulted in IL-21R up-regulation.

Microbial translocation and the associated immune activation during HIV-1 infection may lead to high expression levels of the IL-21R activation marker in RM B cells, a feature associated with increased apoptosis and a reduced number of these cells in the circulation.