Page 321 - Anatomy and Physiology of Farm Animals, 8th Edition

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(Table 16‐1). Immunoglobulin (Ig) G is the the same allergen is again encountered, the
allergen binds to the specific IgE on the
predominant circulating immunoglobulin.
VetBooks.ir IgG has a variety of functions, including: mast cells, and this stimulates the mast
cells to release their secretory granules
(1) binding free circulating antigens to
reduce their potential for harm (neutrali- containing histamine and produce leukot-
zation) and promote their removal by rienes. These agents bring about many of
phagocytes; (2) binding antigens associ- the cell and tissue responses characteristic
ated with bacterial cell walls and promot- of allergies. IgA is most often associated
ing their phagocytosis; (3) binding antigens with the immune response in the intestines
and activating complement to promote and other mucosa‐associated lymphatic
inflammation and destruction of harmful tissues. Mammary secretions contain high
microbes; and (4) acting as an agglutinin to amounts of IgA and are a significant source
clump particulates so that they can be of immune defense against respiratory and
more effectively phagocytized. IgG does gastrointestinal pathogens in the suckling
not actually destroy any harmful substance neonate. For more information regarding
or agent; it promotes destruction or the role of the immunoglobulins in neona-
removal indirectly. tal health, see Chapter 29. The fifth class of
IgM is physically the largest of the immunoglobulins is IgD, which is the least
immunoglobulins and it is the first to be prevalent type of immunoglobulin and
produced in response to a novel antigen. serves as a B cell activator in conjunction
IgE is the class of immunoglobulins associ- with IgM. IgD has been identified in
ated with most allergic responses. When domestic species using genomic sequenc-
an allergen (an agent capable of inducing ing, but is still poorly characterized.
an allergic response) is first encountered,
specific IgE is produced and incorporates
into the cell membrane of mast cells. When T Cells and Cell‐Mediated
Immunity

Table 16-1. General Characteristics T cells are the type of lymphocyte associ-
of Classes of Immunoglobulins ated with the component of an immune

Class General Characteristics response known as cell‐mediated immu-
IgG Most abundant immunoglobulin in nity. Whereas the humoral response
involves antibodies that can have their
circulation. Protective against bacteria and
viruses, neutralizes toxins, and activates effect at sites distant from their site of pro-
complement. Provides for passive duction, the cell‐mediated immune
immunity in newborns. response requires that the responding T
IgA Primarily found in secretions associated cells be in contact with the cells bearing
with epithelial surfaces and mucous the foreign antigen. As with B cells, T cells
membranes where it provides localized have various subtypes, each with its
protection against bacteria and viruses. specific functions. The subtypes include
IgE Contributes to allergic responses by cytotoxic T cells, helper T cells, memory T
binding to mast cells and basophils to cells (Fig. 16‐1), and NK T cells. NK T cells
promote release of mediators of allergic
reactions. Also contributes to protection and helper T cells are introduced earlier in
against parasites. this chapter.
IgM First immunoglobulin produced by plasma As with the humoral response, antigen
cells in response to exposure to antigen. recognition initiates the cell‐mediated
Contributes to natural antibodies such as response. However, antigen recognition by
those associated with blood cell typing. T cells requires that the antigenic material
IgD Least abundant of the immunoglobulins. be presented as part of a complex on the
Believed to function as a B cell antigen cell membrane of other immune cells. This
receptor. complex consists of the antigenic material