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