Immunity Innate and Adaptive Immunity Cells of the

Immunity Ø Innate and Adaptive Immunity Ø Cells of the Immune System Ø Physical & Chemical Barriers

Innate and Adaptive Immunity Ø Innate Defenses u Nonspecific physical and chemical barriers that contribute to resistance against infection u Does not exhibit immunological memory u Mediated several classes of cells and tissues, with close interactions with the adaptive response

Innate and Adaptive Immunity Ø Adaptive Immunity u Response to specific biochemical groups that distinguishes between “self” and “nonself” u Antigen: Any substance that the adaptive immune system responds to u Exhibits “immunological memory: ” Once the immune system has been exposed to an antigen, the response in subsequent exposures is much faster and stronger u Mediated by lymphocytes

Cells of the Immune System Ø Monocytes u Function and macrophages as phagocytic cells u Typically have round or horseshoe-shaped nuclei u Monocytes circulate in the blood & lymph; macrophages are derived from monocytes that have moved from the blood & lymph into surrounding tissue u Both are active as phagocytes

Cells of the Immune System Ø Polymorphonuclear u Irregular-shaped granulocytes nuclei and cytoplasm with vesicles (granules) filled with hydrolytic enzymes u Neutrophiles: Function primarily as phagocytes u Eosinophiles: Function by degranulation in response to larger parasites u Basophiles: Also function predominantly by degranulation; similar to mast cells and releases histamine

Cells of the Immune System Ø Dendritic u. A Cells class of phagocytes associated with tissues in contact with the external environment, such as skin, mucous membranes, & the intestinal lining u 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 Ø Lymphocytes u Responsible for the adaptive immune response u Each lymphocyte cell possesses a receptor that can bind to a specific molecular group on an antigen u 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 Ø Lymphocytes u Primary lymphocytes are lymphocytes that have never responded to antigen u Primary lymphocytes respond to antigen by clonal selection, clonal expansion, and differentiation into effector cells and secondary (memory) lymphocytes u Secondary lymphocytes are able to respond more rapidly and effectively to subsequent exposures to the antigen

Cells of the Immune System Ø Lymphocytes u Two classes of lymphocytes: T lymphocytes and B lymphocytes u 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 Ø Lymphocytes u. T lymphocytes formed in the thymus gland during an immune response, T lymphocyes may differentiate into several different classes of effector cells Helper T lymphocytes (TH or CD 4+ T cells) secrete cytokines that stimulate the activity of other immune cells, including B lymphocytes and other T cells Cytotoxic T lymphocytes (TC or CD 8+ 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 Ø Ø Ø Skin Barrier Mucous membranes Lysozyme u Antibacterial enzyme found in tears Complement u A series of proteins in the blood and tissue fluid that can mediate cytolytic processes Inflammation u 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 Ø Antibodies (Immunoglobulins) u Proteins secreted from plasma cells (which have differentiated from B lymphocytes) u 5 different classes of immunoglobulins: Ig. M: Represents the cell-surface receptor on B lymphocytes; also is the first Ig to be secreted in a primary immune response Ig. D: A minor Ig Ig. G: The major immunoglobulin found in blood & tissue fluid Ig. A: Found in secretions such as saliva and breast milk Ig. E: Stimulates mast cells & causes them to release histamine

Physical & Chemical Barriers Ø Antibodies u Antibody (Immunoglobulins) molecules bind with great specificity and affinity to the antigen that originally activated the B lymphocyte u Each antibody molecule has two or more sites for binding antigen, so antigen molecules can be cross-linked, as in precipitation or aggluttination reactions u Antibodies play a number of essential roles in an effective immune response

Physical & Chemical Barriers Ø Antibodies (Immunoglobulins) u 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