Page 448 - Veterinary Immunology, 10th Edition

VetBooks.ir B Cell Response

Once it receives help from the multiple sources described above, the
B cell is ready to respond.

Differential Signaling

Like the TCR, the BCR probably produces a tunable signal. That is,
it generates signals that depend on the properties of the antigen and
the amount of co-stimulation received. The affinity of a BCR for its

antigen influences B cell proliferation and antibody secretion. On
the other hand, receptor occupancy influences MHC class II
expression and signal transduction. The direction of the
immunoglobulin class switch also depends on signals received

from Th1 or Th2 cytokines.
Certain antigens can provoke antibody formation in the absence
of helper T cells. These so-called T-independent antigens are
usually simple repeating polymers (and PAMPs), such as

Escherichia coli lipopolysaccharide, polymerized salmonella
flagellin, and pneumococcal polysaccharide. T-independent
antigens bind directly to B cell TLRs and cross-link several BCRs,
providing a sufficient signal for B cell proliferation.

Characteristically, T-independent antigens only trigger IgM
responses and fail to generate memory cells (Fig. 15.12).

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