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 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 and macrophages Function 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 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 Cells A 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 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