Circulating anergic B cells in the periphery of active systemic lupus erythematosus patients: functional and phenotypic characterization

Abstract

A CD19lowIgD+ B-cell population that was observed in the periphery of active systemic lupus erythematosus (SLE) patients, but not in nonautoimmune normal individuals, was examined to determine its functional and phenotypic characteristics. Whereas CD19lowIgD- cells in the periphery of SLE patients are intracytoplasmic (IC) Ig+ plasma cells, CD19lowIgD+ cells are IC Ig-. In contrast to CD19highIgD+ B cells, CD19lowIgD+ B cells are small, in the G0/G1 phase with very few cells in the S/G2/M phase or undergoing apoptosis, remain viable in the G0/G1 phase in short-term culture without additional stimulation, and are positive for the anti-apoptotic gene A20. Additionally, in contrast to CD19highIgD+B cells, CD19lowIgD+ B cells are less activated, as assessed by lower expression of activation markers such as CD69, CD154, CD38, CD27, CD86 and CD11c. Moreover, CD19lowIgD+ B cells express a higher level of CD5, CD21 and CD23 when compared with CD19highIgD+ B cells. Furthermore, CD19lowIgD+ B cells have less mutated heavy chain Ig genes as assessed by single-cell PCR of genomic DNA, and do not express AID when compared with CD19highIgD+ B cells. Whereas CD19highIgD+ B cells were rescued from apoptosis and driven into the S/G2/M phase following stimulation with a low amount of anti-IgM antibody or rCD154, CD19lowIgD+ B cells required 100-fold more stimulation to rescue them from apoptosis and drive them into cell cycle. Of interest, CD19lowIgD+ B cells exhibit higher amounts of BCR, phosphorylated CD19 and phosphorylated lyn in cytoskeletal-associated membrane fractions compared with CD19highIgD+ B cells. Clinically, the number of circulating CD19lowIgD+ B cells in SLE patients is greater in those with normal complement levels. Treatment of SLE patients with a blocking anti-CD154 antibody diminishes the presence of circulating CD19lowIgD+ B cells. Together, these results indicate that CD19lowIgD+ cells in the periphery of SLE patients may be a functionally anergic population of in vivo stimulated B cells that disappear when the disease becomes quiescent.