Page 442 - Veterinary Immunology, 10th Edition

immunoglobulin class switching.
VetBooks.ir themselves encounter the antigen. This antigen can be presented by
In order to do all this, however, the helper T cells must

one of the professional antigen-presenting cells, such as dendritic

cells, macrophages, or even B cells. Thus a B cell can capture and
process antigen, present it to a T cell, and then receive co-
stimulation from the same T cell. B cells thus play two roles. They
respond to antigen by making antibodies while at the same acting

as antigen-processing cells. The helper T cells provide B cells with
co-stimulatory signals from cytokines as well as through interacting
receptor pairs.

Cytokine Secretion

Th2 cells produce multiple cytokines that activate B cells. The most
important of these are interleukin-4 (IL-4), IL-5, IL-6, IL-13, and IL-
21.
IL-4 stimulates the growth and differentiation of B cells and
enhances their expression of MHC class II and Fc receptors. It also

induces immunoglobulin class switching and thus stimulates IgA
and IgE production (Table 15.1). The actions of IL-4 are neutralized
by IFN-γ, which inhibits both IgA and IgE synthesis as well as B

cell proliferation.

TABLE 15.1

Immunoglobulins Produced by B Cells in the Presence of Th1
and Th2 Antigen-Specific Helper T Cell Clones in Mice

Th1 Cells Th2 Cells
Class
(ng/mL) (ng/mL)
IgG1 <8 21,600
IgG2a 14 39
IgG2b <8 189
IgG3 <8 354
IgM 248 98,000
IgA <1 484
IgE <1 187
Adapted from Coffmann RL, Seymour BW, Lebman DA, et al: The role of helper T cell
products in mouse B cell differentiation and isotype regulation, Immunol Rev 102:5, 1988.

IL-5 promotes the differentiation of activated B cells into plasma
cells. It stimulates IgG and IgM production and enhances IL-4-
induced IgE production. IL-5 selectively stimulates IgA production

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