Page 443 - Veterinary Immunology, 10th Edition

in mucosal B cells.
VetBooks.ir plasma cells. It acts together with IL-5 to promote IgA production
IL-6 is needed for the final differentiation of activated B cells into

and with IL-1 to promote IgM production.

IL-13 has biological activities similar to those of IL-4 because it
acts through a receptor (IL-13R) that shares a common α chain with
the IL-4R. This stimulates B cell proliferation and increases
immunoglobulin secretion. IL-13 is required for optimal induction

of IgE, especially if IL-4 is low or absent.
IL-21 is produced by several Th populations including both Tfh
cells and Th17 cells. It induces the differentiation of B cells into
plasma cells and memory B cells. It stimulates IgG production in

conjunction with IL-4. IL-21 promotes the IgM to IgG class switch,
while IL-4 induces the switch to IgE.

Cell-Cell Signaling

Cytokines alone cannot fully activate B cells. Complete activation
also requires signaling between Th cells and B cells through

receptor pairs such as CD40 and CD154. CD154 is expressed on
activated helper T cells while its receptor CD40 is expressed on
resting B cells. CD40 must receive a signal from CD154 in order for

the B cell to begin its cell cycle and upregulate its IL-4 and IL-5
receptors (Figs. 15.9 and 15.10). The signals from CD154 synergize
with those from IL-4 and IL-5 receptors to drive B cell activation,
memory cell development, and immunoglobulin class switching.
CD28, also found on helper T cells must also provide co-stimulation

by binding CD86 on activated B cells.

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