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Lecture 25

PSL201Y1 Lecture Notes - Lecture 25: T Helper Cell, Cytotoxic T Cell, Natural Killer Cell

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Hae- Young Kee

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Lecture 25
-helper T cells producing lymphokines in absence of lymphokines produced by Helper T ells,
remainder of immune system is almost paralyzed helper T cells that are inactivated destroyed
by HIV virus that leaves body almost totally unprotected against infectious diseases AIDS
treatment involve use of drugs that inhibit reverse transcriptase , enzyme used by virus to
replicate its RNA current therapy don’t cure AIDS
-as helper T ells differentiate they produce secretory (effector cells) and memory cells secretory
cells secrete cytokines that stimulate and regulate immune response and they act on number of
cell types: helper T cells, B cells, cytotoxic T cells, macrophages, mast cells, natural killer cells,
hematopoietic stem cells
-helper T cells among the important lymphokines secreted by the helper T ells are following
IL2, IL3, Il4, IL5, IL6, granulocyte-monocyte colony stimulating factor interferon gamma
-cytotoxic T cell is a direct attack cell capable of killing microorganisms and even body’s own
cells receptor proteins on surface on cytotoxic cell causes them to bind tightly to those
organisms or cells that contain appropriate binding specific antigens then they kill the cell after
binding, they secrete pore forming proteins called perforins, they punch large holes in
membrane of attacked cells consequently fluid from interstitium rushes into these cells creating
osmotic gradient cells also secrete fragmentins that enter infected cells through these pores
and trigger apoptosis cytotoxic killer cells also release cytotoxic substances directly to attacked
cells, almost immediately, the attacked cell becomes greatly swollen and dissolving shortly after,
these cytotoxic killer cells can pull away from victim cells move on to kill more cells some of
these cells persist for months in tissues, they play a role in transplant and cancer cells
-actions of activated cytotoxic cells in tumor cells tumor cells possess distinctive molecules
called tumor antigens not present on normal cells class 1 MHC that normally exist on tumor
cells, present fragments of these antigens to cytotoxic T cells and initiate killing response
certain cancers and viruses, they actively inhibit production of class 1 MHC on affected cells so
enable these to escape detection by cytotoxic T cells
-suppressor T cells regulate activities of the other cell and prevent excessive immune reactions
that may be damaging to body’s own tissue play a role in immune tolerance
-helper T cell activated in 2 ways firstly by specific contact with macrophage viral antigen by
class 2 MHC, secondly, can activated by interleukin 1 secreted by macrophages this activated
helper T cell undergoes cell proliferation resulting in differentiation of memory helper T cell and
daughter helper cells that secrete more interleukin 2 IL-2 secreting helper T cells play a role in
B lymphocytes activation and IL-2 also activates cytotoxic T cells B lymphocyte is activated by
specific contact with free floating antigen, in context of helper cell activation, IL2 secreted by
helper T cell also activate B cells leading B cell proliferation and production of plasma cells and
producing antibodies and memory cells
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