T-Lymphocytes

Initial response of body to infection is non-specific (phagocytes).Immunity is the ability of an organism to resist infection by protecting against disease-causing organisms or their toxins that invade their body. Involves recognition of foreign material antigens - it is called specific immunity. Action is slower at first but provides long term immunity.There are two types of lymphocyte produced by stem cells in bone marrow: T-lymphocytes mature in thymus and associated with cell-mediated immunity which involves body cells. B-lymphocytes mature in bone marrow and associated with humoral immunity which involves antibodies present in body fluids.

T-LymphocytesRespond to organism's own cells infected with non-self material from a different species e.g. virus.Also respond to cells from other individuals as they are genetically different.T-lymphocytes can distinguish invader cells by normal cells because: Phagocytes engulf and hydrolyse pathogen and place pathogen's antigens on its surface. Body cells invaded by a virus present some viral antigens on cell surface membrane. Cancer cells different from body cells and present antigens on cell surface membranes.

Stages of a T-lymphocyte responding to infection by pathogen: Pathogen invades body cell. T-lymphocytes have specific membrane-bound receptor proteins which bind to antigens. Activated by specific antigen. * Activated T-lymphocytes cloned by mitosis. Cloned T-lymphocytes differentiate into T-cells with different functions. ** * T-lymphocytes can be activated by specific antigen on: Pathogens engulfed and hydrolysed by phagocyte. Body cells invaded by a virus. Cancer cells. ** T-lymphocytes can differentiate into T-cells with different functions: Cytotoxic / killer T-cells migrate to site of infection, bind to antigens and kill the infecting cells - produce perforin protein which makes holes / pores in cell surface membrane of pathogen thus membrane becomes more permeable, water diffuses in by osmosis and cell bursts. Helper T-cells bind to antigens on infecting cells and secrete chemicals that activate and stimulate phagocytes, cytotoxic T-cells as well as stimulate B-lymphocytes, speeding up immune response. Memory T-cells remain in blood decades after infection - if same antigen enters body again, it will be identified quickly, memory T-cells will quickly divide to form cytotoxic and helper Stimulate phagocytes to engulf pathogens by phagocytosis.