Defense Mechanisms of the Body
677
Table 18–12
A Miniglossary of Cells and Chemical Mediators Involved in Immune Functions
(continued)
Chemical Mediators
Acute phase proteins
Group of proteins secreted by the liver during systemic response to injury or infection; stimulus for their secretion
is IL-1, IL-6, and other cytokines.
Antibodies
Immunoglobulins secreted by plasma cells; combine with the type of antigen that stimulated their production and direct an
attack against the antigen or a cell bearing it.
C1
The fi rst protein in the classical complement pathway.
Chemoattractants
A general name given to any chemical mediator that stimulates chemotaxis of neutrophils or other leukocytes.
Chemokines
Any cytokine that functions as a chemoattractant.
Chemotaxin
A synonym for chemoattractant.
Complement
A group of plasma proteins that, upon activation, kill microbes directly and facilitate the various steps of the infl
ammatory
process, including phagocytosis; the classical complement pathway is triggered by antigen-antibody complexes, whereas the alternate
pathway can operate independently of antibody.
C-reactive protein
One of several proteins that function as nonspecifi c opsonins; production by the liver is increased during the acute
phase response.
Cytokines
General term for protein messengers that regulate immune responses; secreted by macrophages, monocytes, lymphocytes,
neutrophils, and several nonimmune cell types; function both locally and as hormones.
Eicosanoids
General term for products of arachidonic acid metabolism (prostaglandins, thromboxanes, leukotrienes); function as
important infl
ammatory mediators.
Histamine
An infl ammatory mediator secreted mainly by mast cells; acts on microcirculation to cause vasodilation and increased
permeability to protein.
IgA
The class of antibodies secreted by the lining of the body’s various “tracts.”
IgD
A class of antibodies whose function is unknown.
IgE
The class of antibodies that mediate immediate hypersensitivity and resistance to parasites.
IgG
The most abundant class of plasma antibodies.
IgM
A class of antibodies that is produced fi rst in all immune responses. Along with IgG, it provides the bulk of specifi c humoral
immunity against bacteria and viruses.
Immunoglobulin (Ig)
Proteins that function as B-cell receptors and antibodies; the fi ve major classes are IgA, IgD, IgE, IgG, and IgM.
Interferon
Group of cytokines that nonspecifi
cally inhibits viral replication; interferon-gamma also stimulates the killing ability of NK
cells and macrophages.
Interferon-gamma
(See
Interferon
)
Interleukin 1 (IL-1)
Cytokine secreted by macrophages (and other cells) that activates helper T cells, exerts many infl
ammatory
effects, and mediates many of the systemic acute phase responses, including fever.
Interleukin 2 (IL-2)
Cytokine secreted by activated helper T cells that causes helper T cells, cytotoxic T cells, and NK cells to
proliferate, and causes activation of macrophages.
Interleukin 6 (IL-6)
Cytokine secreted by macrophages (and other cells) that exerts multiple effects on immune system cells,
infl ammation, and the acute phase response.
Kinins
Peptides that split from kininogens in infl amed areas and facilitate the vascular changes associated with infl ammation; they also
activate neuronal pain receptors.
Leukotrienes
A class of eicosanoids that are generated by the lipoxygenase pathway and function as infl
ammatory mediators.
Membrane attack complex (MAC)
Group of complement proteins that form channels in the surface of a microbe, making it leaky and
killing it.
Natural antibodies
Antibodies to the erythrocyte antigens (of the A or B type).
Opsonin
General name given to any chemical mediator that promotes phagocytosis.
Perforin
Protein secreted by cytotoxic T cells and NK cells that forms channels in the plasma membrane of the target cell, making it
leaky and killing it; its structure and function are similar to that of the MAC in the complement system.
Tumor necrosis factor (TNF)
Cytokine secreted by macrophages (and other cells) that has many of the same actions as IL-1.
previous page 705 Vander's Human Physiology The Mechanisms of Body Function read online next page 707 Vander's Human Physiology The Mechanisms of Body Function read online Home Toggle text on/off