Page 441 - Veterinary Immunology, 10th Edition

VetBooks.ir Co-stimulation of B Cells

Although the binding of antigen to a BCR is an essential first step, it
alone is usually insufficient to activate B cells. Complete activation

of a B cell requires multiple signals from other sources. Thus it
requires co-stimulation by helper T cells and cytokines, by
complement, and by pathogen-associated molecular patterns
(PAMPs; Fig. 15.8).

FIG. 15.8 Not only must B cells be stimulated by antigen, but they
must also receive costimulation from helper T cells and their
cytokines, as well as complement and PRRs, if they are to respond
optimally.

T Cell Help

When helper T cells “help” B cells they promote several different B

cell activities. These signals result in increased expression of IgM
BCR and MHC class II, as well as receptors for IL-4, IL-5, IL-6,
tumor necrosis factor-α (TNF-α), and transforming growth factor-β
(TGF-β), and start the process that leads to B cell division and

differentiation into antibody-secreting cells. They stimulate B cell
proliferation and survival through CD40L, IL-21, and IL-4. The
“help” also triggers somatic mutation within germinal centers and
thus changes antibody binding affinity. Helper T cells also trigger

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