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Immunity
 Innate
and Adaptive Immunity
 Cells of the Immune System
 Physical & Chemical Barriers
Innate and Adaptive Immunity
 Innate
Defenses
 Nonspecific
physical and chemical barriers
that contribute to resistance against
infection
 Does not exhibit immunological memory
 Mediated several classes of cells and
tissues, with close interactions with the
adaptive response
Innate and Adaptive Immunity
 Adaptive
Immunity
 Response
to specific biochemical groups
that distinguishes between “self” and
“nonself”
 Antigen: Any substance that the adaptive
immune system responds to
 Exhibits “immunological memory:” Once the
immune system has been exposed to an
antigen, the response in subsequent
exposures is much faster and stronger
 Mediated by lymphocytes
Cells of the Immune System
 Monocytes
 Function
and macrophages
as phagocytic cells
 Typically have round or horseshoe-shaped
nuclei
 Monocytes circulate in the blood & lymph;
macrophages are derived from monocytes
that have moved from the blood & lymph
into surrounding tissue
 Both are active as phagocytes
Cells of the Immune System
 Polymorphonuclear
 Irregular-shaped
granulocytes
nuclei and cytoplasm with
vesicles (granules) filled with hydrolytic
enzymes
 Neutrophils: Function primarily as
phagocytes
 Eosinophils: Function by degranulation in
response to larger parasites
 Basophils: Also function predominantly by
degranulation; similar to mast cells and
releases histamine
Cells of the Immune System
 Dendritic
A
Cells
class of phagocytes associated with
tissues in contact with the external
environment, such as skin, mucous
membranes, & the intestinal lining
 Dendritic cells act as “antigen-presenting
cells” - they phagocytize targets such as
bacteria, process the bacterial antigens and
“present” them to lymphocytes
Cells of the Immune System
 Lymphocytes
 Responsible
for the adaptive immune
response
 Each lymphocyte cell possesses a receptor
that can bind to a specific molecular group
on an antigen
 There are believed to be millions of different
receptor specificities, but each lymphocyte
only expresses a single type of receptor on
its surface
Cells of the Immune System
 Lymphocytes
 Primary
lymphocytes are lymphocytes that
have never responded to antigen
 Primary lymphocytes respond to antigen by
clonal selection, clonal expansion, and
differentiation into effector cells and
secondary (memory) lymphocytes
 Secondary lymphocytes are able to respond
more rapidly and effectively to subsequent
exposures to the antigen
Cells of the Immune System
 Lymphocytes
 Two
classes of lymphocytes: T lymphocytes
and B lymphocytes
 B lymphocytes
formed in the bone marrow of mammals or the
Bursa of Fabricus in birds
 during an immune response, B lymphocyes
differentiate into plasma cells that secrete
antibody protein specific for the antigen(s)
encountered

Cells of the Immune System
 Lymphocytes
T
lymphocytes
formed in the thymus gland
 during an immune response, T lymphocyes may
differentiate into several different classes of
effector cells
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Helper T lymphocytes (TH or CD4+ T cells) secrete
cytokines that stimulate the activity of other immune
cells, including B lymphocytes and other T cells
Cytotoxic T lymphocytes (TC or CD8+ T cells) destroy
virally-infected cells and tumor cells, and are
responsible for transplant rejection
Regulatory T lymphocytes (Treg cells) help to mediate
immunotolerance
Physical & Chemical Barriers
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Skin Barrier
Mucous membranes
Lysozyme
 Antibacterial enzyme found in tears
Complement
 A series of proteins in the blood and tissue fluid that can
mediate cytolytic processes
Inflammation
 Activation of immune cells in a damaged or infected
region causes vasodilation, chemotaxis of leukocytes
into the region, and diapedesis (movement of leukocytes
from the capillaries into the surrounding tissue)
Physical & Chemical Barriers

Antibodies (Immunoglobulins)
 Proteins secreted from plasma cells (which have
differentiated from B lymphocytes)
 5 different classes of immunoglobulins:
 IgM: Represents the cell-surface receptor on B
lymphocytes; also is the first Ig to be secreted in a
primary immune response
 IgD: A minor Ig
 IgG: The major immunoglobulin found in blood &
tissue fluid
 IgA: Found in secretions such as saliva and breast
milk
 IgE: Stimulates mast cells & causes them to release
histamine
Physical & Chemical Barriers
 Antibodies
 Antibody

Two types, κ and λ
Two heavy chains
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structure
Two light chains
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(Immunoglobulins)
Five different types: μ, δ, γ, α, and ε
Class specific
Each heavy and light chain has two regions
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Variable region
Constant region
http://en.wikipedia.org/wiki/Antibody
Physical & Chemical Barriers
 Antibodies
 Antibody
(Immunoglobulins)
molecules bind with great
specificity and affinity to the antigen that
originally activated the B lymphocyte
 Each antibody molecule has two or more
sites for binding antigen, so antigen
molecules can be cross-linked, as in
precipitation or aggluttination reactions
 Antibodies play a number of essential roles
in an effective immune response
Physical & Chemical Barriers

Antibodies (Immunoglobulins)
 Roles of Antibodies
 Precipitation: Clumping and precipitation of soluble
antigens
 Agglutination: Clumping together of cellular antigens
 Virus neutralization
 Toxin neutralization
 Complement fixation: Antibody molecules can trigger
a complement pathway leading to the lysis of a
cellular antigen
 Opsonization: Antibody molecules can coat a cellular
antigen, making it much easier for a phagocyte to
recognize and engulf