Page 439 - Veterinary Immunology, 10th Edition

VetBooks.ir Antigen Presentation by B Cells

B cells are effective antigen-presenting cells. Following antigen
binding, the BCR is internalized and either degraded or transported

to an intracellular compartment, where major histocompatibility
(MHC) class II molecules and antigen fragments combine. These
antigen-MHC class II complexes are then carried to the B cell
surface and presented to helper T cells (Fig. 15.7). If antigen
presented by an APC binds to a BCR, the antigen may be extracted

from the presenting cell and endocytosed by the B cell. This antigen
is delivered to endosomes where it also complexes with MHC class
II molecules. Since all the antigen receptors on a single B cell are

identical, each B cell can bind only one antigen. This makes them
much more efficient antigen-presenting cells than macrophages that
must present any foreign material that comes their way. This is
especially true in primed animals, in which large numbers of B cells
can bind and present a specific antigen. As a result, B cells can

activate Th cells with 1/1000 of the antigen required to activate
macrophages.

FIG. 15.7 The processing of antigens by B cells. This is a very
efficient process since the BCRs capture large amounts of identical

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