immunity innate and adaptive immunity cells of the immune system physical & chemical barriers
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Immunity
Innate and Adaptive Immunity Cells of the Immune System Physical & Chemical Barriers
Innate and Adaptive Immunity
Innate DefensesNonspecific physical and chemical barriers
that contribute to resistance against infection
Does not exhibit immunological memoryMediated several classes of cells and
tissues, with close interactions with the adaptive response
Innate and Adaptive Immunity
Adaptive ImmunityResponse 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 and macrophagesFunction as phagocytic cellsTypically have round or horseshoe-shaped
nucleiMonocytes 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 granulocytes Irregular-shaped 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 CellsA 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
LymphocytesResponsible for the adaptive immune
responseEach 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
LymphocytesPrimary lymphocytes are lymphocytes that
have never responded to antigenPrimary 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
LymphocytesTwo classes of lymphocytes: T lymphocytes
and B lymphocytesB 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
LymphocytesT lymphocytes
formed in the thymus glandduring an immune response, T lymphocyes may
differentiate into several different classes of effector cells
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
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 (Immunoglobulins)Antibody structure
Two light chains Two types, κ and λ
Two heavy chains Five different types: μ, δ, γ, α, and ε Class specific
Each heavy and light chain has two regions Variable region Constant region
http://en.wikipedia.org/wiki/Antibody
Physical & Chemical Barriers
Antibodies (Immunoglobulins)Antibody 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