IMMUNE RESPONSE
1. Immunity means protection from disease and especially infectious disease. Cells and molecules involved in such protection constitute theimmune system and the response to introduction of a foreign agent is known as the immune response.
2. Not all immune responses protect from disease; some foreign agents, such as the
allergens found in house dust mite, cat dander or rye grass pollen, cause disease as
a consequence of inducing an immune response.
3. Likewise some individuals mount immune responses to their own tissues as if they were foreign agents. Thus, the immune response can cause the autoimmune diseases common to man such as multiple sclerosis, diabetes, rheumatoid arthritis or myasthenia gravis.
4. Most individuals do not suffer from autoimmune disease because they have developed tolerance towards their own (self) tissues.
Humoral And Cell Mediated Immune response
1. Humoral immunity produces antibodies in response to toxins (ex bee venom), free
bacteria, and viruses present in the body fluids.
2. "Humor” is medieval term for body fluids. Here it refers to the fluid of the blood and the lymph.
3. Antibodies to these types of antigens are synthesized by B- lymphocytes and then
secreted as soluble proteins which circulate through the body in blood plasma and
lymph.
4. Cell-mediated immunity is the response to intracellular bacteria and viruses, fungi,
protozoans, worms, transplanted tissues, and cancer cells.
5. Depends on the direct action of various types of T-lymphocytes rather than antibodies.
6. T-lymphocytes differentiate into 4 different varieties of T-cells.
• Helper/inducer T-cells (Links Cell meduated and Humoral Immunity)
• Suppressor T cells (Suppresses the immune response when antigens are disposed off)
• Cytotoxic T cells or killer cells (Effector cells of cell mediated immunity)
• Memory T-cells
.
7. “Memory B and T cells” are cells that have been exposed to an antigen and are readily converted to “Effector cells” by a later encounter with the same antigen. Unlike other lymphocytes, they persist in the body for months or even years.
8. The killer T-cells directly attack and destroy antigens. They move to the site of
invasion and produce chemicals that attract phagocytes. Helper T-cells act to stimulate
antibody production by B-cells, while suppressor T-cells suppresses the total immune system from attacking the body’s own cells.
9. Thymus-Independent Antigens: Some bacterial polysaccharides can active B-cells.
Antigens capable of doing so are called thymus independent antigens because these antigens do not require the cooperation of Helper T-cells for activating B-cells.
Thymus dependent antigens; many antigens require the cooperation of T-cells for activating B-cells. The antigens present on organ transplant are thymus dependent
antigens. So a person whose thymus gland is removed is not able to reject organ
transplant.
10. MHC are major histocompatibilty complex (glycoproteins) prensent on cells which present processed intracellular antigen to T-Lymphocytes. They are also called as Human Leucocyte Antigen (HLA) in humans.
11. MHC-I is present on all nucleated cells and are recognized by CD 8+ arms of T-
Cytotoxic cells and present processed antigen to T-cytotoxic cells while MHC-II are present on T & B lymphocytes, dendritic cells and mast cells and recognized via CD
4+ arm present on T-Helper cell.
12. Lymphokines: They are a family of soluble chemical mediator released by helper T-cells. Lymphokines have two broad functions. One group of lymphokines is concerned with growth and differentiation of B and T cells. The other group helps phagocytosis by attracting phagocytic cells when required through chemotaxis and by activating the phagocytic cells.
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