T helper cell undergoes differentiation process during which a variety of

T helper cell undergoes differentiation process

This preview shows page 160 - 167 out of 295 pages.

T helper cell undergoes differentiation process during which a variety of cytokine genes are activated. Depending on the pattern of cytokines expressed, the mature T helper cell interacts with either immunocompetent B or T cells to enhance their response to antigen. This results in differentiation into either plasma cells or effector T cells (i.e. cytotoxic T cells). 160
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Induction of an Immune Response: Clonal Selection T helper lymphocytes: Critical to most immune responses. Variety of T helper cell defects can lead to severely diminished immune responses . 161
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Induction of an Immune Response: Clonal Selection T helper lymphocytes: Cells destined to become T helper cells emerge from the thymus gland with characteristic cell surface markers. Cells have a functional alpha-beta T cell receptor complex, and express the surface molecule CD4 and lack CD8 . Generally referred to as precursor T helper cells. T cell receptor recognizes antigen, and the CD4 molecule confines antigen presentation to the MHC class II molecules. 162
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Induction of an Immune Response: Clonal Selection T helper lymphocytes: In order to undergo maturation, the T helper cell must receive three independent signals. Antigen binding through the combined interaction of the T cell receptor complex and CD4. Stimulatory signals through a variety of intercellular adhesion molecules. Activation of specific cytokine receptors. When the appropriate signaling pathways are activated, the cell will differentiate through multiple intermediate stages into functional T helper cells. 163
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Induction of an Immune Response: Clonal Selection T helper lymphocytes: Antigenic signal alone is inadequate and may even inactivate the T helper cell if co-stimulatory signals are not present. Co-stimulatory molecules are necessary for proper differentiation to occur. 164
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Induction of an Immune Response: Clonal Selection T helper lymphocytes: Other interactions occur between CD4 on the antigen presenting cell and CD2 on the T helper cell, and between other adhesion molecules. T helper cell molecule sends an activation signal to the nucleus. An additional signal is provided by cytokines. At this early stage of T helper cell differentiation, IL-1 created by the antigen presenting cell provides the signal interaction with the IL-1 receptor on the T helper cell. 165
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Induction of an Immune Response: Clonal Selection T helper lymphocytes: Initial differentiation response by the T helper cell includes the production of IL-2 and up regulation of IL-2 receptors. IL-2 is secreted and acts as an autocrine to induce further maturation and proliferation of the T helper cell. Without IL-2 production, the T helper cell cannot sufficiently mature into a functional helper cell. T helper cell now undergoes one of several different differentiation pathways into T helper cell subsets.
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  • cells, Cytotoxic Cells

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