B-lymphocyte antigen CD19, also known as CD19 molecule (Cluster of Differentiation 19), B-Lymphocyte Surface Antigen B4, T-Cell Surface Antigen Leu-12 and CVID3 is a transmembrane protein that in humans is encoded by the gene CD19.

Jul 1, 2001 · The CD19/CD21 complex is an essential B cell coreceptor that functions synergistically to enhance signaling through the B cell Ag receptor in response to T cell-dependent, complement-tagged Ags.

Recent studies with mice that lack CD19 or CD21 or overexpress CD19 suggest that the CD19–CD21 complex serves as a general response regulator that governs humoral immune responses by B cells.

CD19 functions as the dominant signaling component of a multimolecular complex on the surface of mature B cells, alongside complement receptor CD21, and the tetraspanin membrane protein CD81 (TAPA-1), as well as CD225.

The complement receptor 2 (CR2, CD21) is part of a complex (CD21/CD19/CD81) acting as a co‐receptor to the B cell receptor (BCR). Simultaneous triggering of the BCR and CD21 lowers the threshold for B cell activation.

Herein we discuss our current understanding of how CD19/CD21 and CD22 govern the emergence and intensity of BCR-mediated signals, and how alterations in these tightly controlled regulatory activities contribute to autoimmunity in mice and humans.

CD21-/low memory B cells are expanded with age in healthy individuals and in patients with viral infections and autoimmune conditions and are associated with pathogen-specific antibodies as well as key disease manifestations.

The CD19/CD21 complex functions to significantly enhance B cell antigen receptor (BCR) signaling in response to complement-tagged antigens. Recent studies showed that following antigen binding the BCR translocates into plasma membrane lipid rafts that serve as …

CD19 also governs B cell responses initiated through the CD21 receptor, where complement C3d binding to CD21 links humoral immune responses with the innate immune system. Alterations in this signaling pathway can predispose mice and humans to …

Sep 1, 1994 · CD19 and CD21 are B-cell surface molecules that associate with each other and with CD81 and Leu-13 to generate a signal transduction complex that is independent of the antigen receptor.