BIO 226T - Lecture 14 Study Questions

BIO 226T - Lecture 14 Study Questions - Lecture 14 Study...

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Lecture 14 Study Questions 1. Functions of subpopulations of T cells: a) T H 0 cells – a mature T H cell that will differentiate into one of two subtypes (T H 1 or T H 2 cells), depending on the cytokine environment during the activation process b) i) T H 1 – during activation, if a dividing T H 0 cell encounters antigen in a cytokine environment of IL-12 and/or gamma interferon , it will differentiate into a clone of “activated” T H 1 cells ( effector cells ) and memory T H 1 cells. Two helper functions: 1) produce the cytokine IL-2 and help some T C cells divide and differentiate into activated cytotoxic T lymphocytes ( CTL s), effector cells which kill virus-infected cells 2) produce the cytokine gamma interferon and help unactivated macrophages become “activated” to kill the intracellular pathogens within them ii) T H 2 – during activation, if a dividing T H 0 cell encounters antigen in a cytokine environment of IL-4 , it will develop into a clone of “activated” T H 2 cells ( effector cells ) and memory T H 2 cells. Activated T H 2 cells predominantly : 1) secrete IL-4 or IL-5 2) help B cells develop into antibody producing plasma cells c) T C divides and differentiates into a clone of cytotoxic T lymphocytes (CTLs) ( effector cells ) and memory T C cells after interacting with a foreign antigen CTLs lyse virus-infected “target” cells in one of three ways: 1) Perforins – (CTL exocytoses from its granules); proteins which polymerize in the cell membrane forming transmembranous pores . Water and ions enter cell causing osmotic lysis analogous to cell lysis seen with membrane attack complex (MAC attack!) and perforin is structurally similar to complement protein C9 2) Granzymes – (set of enzymes the CTL exocytoses from its granules); enter the virus-infected cell through the perforin-created transmembranous pores once inside the cell, these enzymes proteolytically cleave and activate caspases (another set of enzymes which cleave several substrates and induce virus-infected target cell to undergo apoptosis [programmed cell death]) 3) Activation of the Fas protein – CTL expresses Fas Ligand ( FasL ), a membrane protein, that binds to the protein FAS on virus-infected cells results in activation of caspases triggering apoptosis of virus-infected cell After delivering these lethal “hits,” the CTL is released from its target cell even before the target cell dies ; CTLs are not injured during the target cell killing and can go on to kill other target cells ! 2. Cytokines produced by T H 1 and T H 2 cells cross regulate the development and activity of the opposite subtype (i.e. interferon gamma inhibits proliferation of T H 2 subset, and IL-4 and IL-5 inhibit T H 1 subset development) 3. CTL binds via its complementary TCR (T-cell receptor) to the viral peptide-class I complex displayed on the surface of the virus-infected cell binding strengthened by CD8 on the CTL binding with MHC I molecule on virus-infected cell
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BIO 226T - Lecture 14 Study Questions - Lecture 14 Study...

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