Page 607 - Veterinary Immunology, 10th Edition

• Discuss how antigens regulate immune responses, although very low or very
VetBooks.ir • Explain how antibodies regulate antibody production through negative feedback
high doses of antigen may cause tolerance.

mechanisms.
• Describe the origins and properties of regulatory T cells (Treg cells).
• Discuss the properties and significance of interleukin-10.

• Explain how Th17 cells enhance inflammatory responses by secreting
interleukin-17 (IL-17).
• Describe the properties and significance of IL-17.

• Discuss the role of indoleamine 2,3-dioxygenase in inducing tolerance.
• Discuss briefly how the immune system and the central nervous system are
closely interconnected and influence each other.

The adaptive immune system can recognize and respond to foreign
invaders and can learn from the experience so that the body
responds faster and more effectively when exposed to the invader a
second time. There is, however, a risk associated with this—the risk

of collateral damage. One of the reasons why the adaptive immune
system is so complex is that much effort must be put into ensuring
that lymphocytes will only attack invaders or abnormal cells and
will ignore normal healthy tissues. As might be anticipated, many

different regulatory circuits balance lymphocyte activities and
minimize the chances of inappropriate or damaging responses. In
addition, immune responses are regulated to ensure that they are
appropriate with respect to both quality and quantity.

Since both T and B cells randomly generate antigen-binding
receptors, it is clear that the initial production of self-reactive cells
cannot be prevented. An animal cannot control the amino acid
sequences and hence the binding specificity of these receptors. As a

result, when first generated, as many as 50% of the T cell antigen
receptors (TCRs) and B cell antigen receptors (BCRs) may bind self-
antigens. If autoimmunity is to be avoided, lymphocytes with these
inappropriate receptors must either be destroyed or at least turned

off.

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