Page 391 - Veterinary Immunology, 10th Edition

• Explain how Th17 cells are generated and their function.
VetBooks.ir • Recognize that Treg cells produce suppressive cytokines and regulate the

activities of other helper T cells.

• Understand that α/β helper T cells are the predominant T cells in most mammals
and that γ/δ helper T cells are the predominant circulating T cells in young
ruminants and pigs.

• Identify the major surface proteins characteristic of T cells.
• Define and describe positive and negative selection of T cells.
• Understand and explain the different functions of Th1, Th2, Th17, and T reg

cells.
• Discuss the role of γ/δ T cells in domestic mammals.
• Have a basic understanding of how T cell memory develops.

• Understand the roles of IL-4, IL-17, IL-2, and IL-10.
• Define immunoglobulin superfamily, immunological synapse, Th17 cells, and
Treg cells.

Unlike the innate immune responses that are triggered by a limited
number of molecular patterns on pathogenic microbes, the
lymphocytes of the adaptive immune system are able to recognize
and respond to “everything,” or at least to a large number of very

diverse foreign antigens. They can do this because they have
receptors that bind these antigens and, under the right conditions,
respond by mounting cell-mediated or antibody-mediated immune
responses.

There are four major populations of lymphocytes with antigen-
binding receptors. These include helper and regulatory T cells that
regulate immune responses; effector (or cytotoxic) T cells that
destroy abnormal cells; and B cells that produce antibodies. Each of

these cell types respond to antigens that bind to their receptors.
This chapter describes the first of these major lymphocyte
populations, the helper T cells.
Foreign antigens are trapped and processed by antigen-

presenting cells and then presented to helper T cells. Each T cell is
covered by about 30,000 identical antigen receptors. If these
receptors bind sufficient antigen in the correct manner, a helper T
cell will respond and initiate an immune response. It does this by

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