Page 120 - Veterinary Immunology, 10th Edition

also bind to CR2/CD19 complexes on the B cell. (Remember that
VetBooks.ir several hundred C3 molecules may attach to an antigen molecule as

a result of C3 convertase activity.) Binding to CR2/CD19 enhances B
cell antigen receptor signaling (Chapter15). Conversely, depletion

of C3 is associated with reduced B cell responses. Coating of
antigens with C3d also enables them to bind to CR2 on dendritic
cells, and so permits memory B cells to sample the antigen over
long periods. In the absence of C3, immune complexes will not bind

to follicular dendritic cells in germinal centers (Chapter 12).
Many complement proteins such as C1q, C3b, and C5a also
influence T cell activation. Thus C3 is present within CD4+ T cells
(Chapter 14). This C3 is cleaved when T cells are activated and the

C3a moves to the cell surface. Here it binds to its receptor and
drives T cell cytokine production.

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