Lecture 19

T cells respond to Ags on the surfaces of other cells and each T cell responds to a single Ag. Specificity is due to a specialized T cell receptor, which stimulates clonal proliferation and differentiation to cells that perform particular effector functions, as well as memory T cells. The tremendous diversity of T cell receptors (perhaps 10¹⁸ potential Ags can be recognized) is generated by a mechanism similar to the gene rearrangements and mutational events responsible for Ab diversity.

are primarily regulatory cells. They determine whether an immune response will be made and how intense the response will be. They secrete soluble proteins (lymphokines) that act as signals necessary for B cells and for other specialized T cells to make immune responses.

• can directly destroy specific target cells. They are important to destruction of cancerous cells and virus-infected host cells, but not cell-free virus. There is also a role in response to some intracellular bacteria and a few protozoa and helminths.
• *injects toxin. "ring structures." apoptosis.

• putatively play a role in suppressing immune responses. These cells may not be fully understood. There is evidence that they may be involved in self-tolerance.
• a potential "off signal" to prevent overreaction of the immune system.

• resemble CTL, but do not display the same antigen specificity. They are active against tumor cells and early in the response to viral infections.
• promiscuous

T_H cells secrete hormone-like proteins that act on themselves and other cells.

TNF alpha, lymphotoxin, interleukin 2(IL-2), IL-4, IL-5, IL-6, IL-8, IFN-gamma, TGF-beta, and IL-10

Mediates diverse effects on different cells, including killing of tumor and virus infected target cells.

• May be involved in cell killing by T_C cells. Involved in cytotytic activity of CTL.

A strict requirement for T cell proliferation. Many other important immune functions, including activation of T_C cells and differentiation of B cells into plasma cells.

B cell growth factors required for proliferation and differentiation.

• Pro-inflammatory. A chemoattractant for immune and phagocytic cells to areas of inflammation.
• inhibit growth of certian T cells.

Stimulates higher levels of macrophage anti-microbial activity and may have anti-viral activity.

are lymphokines that regulate immune responses by inhibiting the growth or activity of T cells that secrete other lymphokines.

• Natural active immunity - from acquired infections
• Natural passive immunity - antibodies passed to fetus, transplacentally; or to infant in breast milk.
• Artificial active immunity - by vaccination/immunization.
• Artificial passive immunity - by administration of preformed antibodies in antiserum

Introduction of microbes or their products to the body, in order to induce a state of immunity to infection, or disease due to microorganisms.

• The material used to induce this state of immunity. There are four main types of vaccines. (Live attenuated vaccines, inactivated vaccines, toxoids, substances extracted from infectious agents)

are microbes that are altered in such a way that they are no longer virulent. Vaccination mimics a real infection. Probably the best vaccines (intensity and length of immunity). Examples are oral Poliovirus, measles, mumps, rubella, and yellow fever.

are microbes that are killed by physical or chemical treatment. Examples are Salmonella, Bordetella pertussis, rabies, influenza, and the Salk polio vaccine.

are toxins that have been chemically altered to remove toxicity. Vaccination induces immunity to the intact (unaltered) toxin. Examples include diphtheria toxin and tetanus toxin.

are purified or partially-purified products that are used as vaccines in the absence of microbes. Usually structural proteins or polysaccharides that may induce immunity to the intact organisms. This type of immunity is often short-lived and must be repeated at intervals. An example is the capsule polysaccharide of Streptococcus pneumoniae.