Defective B cell ontogeny and humoral immune response in mice prematurely expressing human complement receptor 2 (CR2, CD21) is similar to that seen in aging wild type mice

Expression and Function of Tetraspanins and Their Interacting Partners in B Cells

Tetraspanins are transmembrane proteins that modulate multiple diverse biological processes, including signal transduction, cell–cell communication, immunoregulation, tumorigenesis, cell adhesion, migration, and growth and differentiation. Here, we provide a systematic review of the involvement of tetraspanins and their partners in the regulation and function of B cells, including mechanisms associated with antigen presentation, antibody production, cytokine secretion, co-stimulator expression, and immunosuppression. Finally, we direct our focus to the signaling mechanisms, evolutionary conservation aspects, expression, and potential therapeutic strategies that could be based on tetraspanins and their interacting partners.

The increased expression of CD21 on AchR specified B cells in patients with myasthenia gravis

CD21, a major complement receptor expressed on B cells, is associated with autoimmune disorders. In the present study, we investigated the role of CD21 in pathogenesis of myasthenia gravis (MG) in relationship to anti-acetylcholine receptor (AchR) IgG (anti-AchR IgG) secretion. We detected increased surface expression of CD21 on AchR specified B cells as well as decreased surface expression of CD21 on total B cells in peripheral blood of patients with generalized MG (gMG). In addition, the serum concentrations of soluble secreted CD21 (sCD21) were decreased in patients with gMG. We also found that the level of CD21(+) AchR specified B cells correlated positively with serum anti-AchR IgG level, while the serum concentration of soluble CD21 correlated negatively with serum anti-AchR IgG level. Our data suggests that CD21 might facilitate its function on AchR specified B cell activation, resulting in the secretion of anti-AchR IgG.

Mice expressing human CR1/CD35 have an enhanced humoral immune response to T-dependent antigens but fail to correct the effect of premature human CR2 expression

We have previously demonstrated that mice expressing human complement receptor type 2 (CR2/CD21) during the CD43(+)/CD25(-) late pro-B cell stage of B cell development have marked changes in their subsequent B cell ontogeny. Here, we show that the humoral immune response to the T cell dependent antigen, sheep red blood cells (SRBCs) can be moderately enhanced with the addition of human CR1 (driven by the lambda promoter/enhancer transgene) to endogenous mCR1/CR2 expression on the B cell surface but that hCR1 expression alone (on the mouse CR1/2 deficient background) has no effect on the humoral immune response or general B cell development. Furthermore, expression of hCR1 had no recuperative effect on the markedly altered B cell phenotype noted with premature expression of hCR2 (either in the presence or absence of endogenous mCR1/2). We conclude that hCR1 alone cannot replace the role of CR2 in mice and that the effects of premature hCR2 expression during BCR development are not significantly altered by the addition of hCR1 at that developmental stage or beyond; thus hCR2 signaling in the mouse remains dominant over subsequent input from either hCR1 or endogenous receptors.