How T Cells Respond to Antigen: Cell-Mediated Immunity (CMI)
T-Cell types and responses are extremely varied. When activated (sensitized) by antigen, a T cell gives rise to one of three different types of progeny, each involved in a cell mediated immune function. The three main functional types of T cells are:
- TH1 cells that activate the CMI pathway
- TH2 cells that assist B-cell processes, and
- TC cells that lead to the destruction of infected host cells and other foreign cells.
Markers on cell surfaces involved in recognition of self and nonself
A given cell can express several different receptors, each type playing a distinct and significant role in detection, recognition, and cell communication. Major functions of receptors are:
- to perceive and attach to non self or foreign molecules (antigens)
- to promote the recognition of self molecules
- to receive and transmit chemical messages among other cells of the system, and
- to aid in cellular development
Clonal selection theory is a scientific theory in immunology that explains the functions of cells (lymphocytes) of the immune system in response to specific antigens invading the body. The concept was introduced by an Australian doctor Frank Macfarlane Burnet in 1957 in an attempt to explain the formation of a diversity of antibodies during initiation of the immune response. The theory has become a widely accepted model for how the immune system responds to infection and how certain types of B and T lymphocytes are selected for destruction of specific antigens.
The theory states that in a pre-existing group of lymphocytes (specifically B cells), a specific antigen only activates (i.e. selection) its counter-specific cell so that that particular cell is induced to multiply (producing its clones) for antibody production. In short the theory is an explanation of the mechanism for the generation of diversity of antibody specificity. The first experimental evidence came in 1958, when Gustav Nossal and Joshua Lederberg showed that one B cell always produces only one antibody. The idea turned out to be the foundation of molecular immunology, especially in adaptive immunity.
The theory states that in a pre-existing group of lymphocytes (specifically B cells), a specific antigen only activates (i.e. selection) its counter-specific cell so that that particular cell is induced to multiply (producing its clones) for antibody production. In short the theory is an explanation of the mechanism for the generation of diversity of antibody specificity. The first experimental evidence came in 1958, when Gustav Nossal and Joshua Lederberg showed that one B cell always produces only one antibody. The idea turned out to be the foundation of molecular immunology, especially in adaptive immunity.
Characteristics of antigens.
Whole cells and viruses make good immunogens. Complex molecules with several epitopes make good immunogens. Poor immunogens include small molecules not attached to a carrier molecule, simple molecules, and large but receive molecules.
Whole cells and viruses make good immunogens. Complex molecules with several epitopes make good immunogens. Poor immunogens include small molecules not attached to a carrier molecule, simple molecules, and large but receive molecules.