View source for Helper T-cells

Helper T cells (CD4+) have the function to induce a response from other immune cells through the production and secretion of cytokines, targeting somatic cells invaded by a foreign antigen. These [[T cells]] can be divided into different subsets. The subsets are based on the expression of particular surface markers and on the cytokine production of the helper T cell<ref>Lodish H, Berk A, Kaiser C.A, Krieger M, Bretscher A, Ploegh H, Amon A, Martin K.C. Molecular Biology. New York: w.h.freeman Macmillan Learning. 2016.</ref>. 

=== Types of Helper T Cells  ===

*'''CD 4-expressing T Helper Cells:''' They help [[B cells]] and to assist them in the process of differentiation into plasma cells. Helper T cells are able to do that by producing and secreting cytokines like [[IL-4]]. In addition, in order to help the particular B cell, the T cell has to be in direct contact with it. 
*'''TH1 Helper Cells:''' These helper cells secrete TNF and interferon gamma. "TNF" stands for tumour necrosis factor. Interferon-gamma helps with the activation of macrophages and stimulation of an inflammatory response. IFNγ allows macrophages to break down intracellular pathogens that have been engulfed or have infected the macrophage. IFNγ is also implicated in switching the Immunoglobulin class of B cells<ref>Alberts et al. Molecular Biology of The Cell. 6th Ed, New York: Garland Science. 2015</ref>. 
*'''TH2 Helper Cells:''' These helper cells secrete [[IL-10]] and IL-4. IL-4 aids B cell class switching to the IgE and IgG1 isotypes. A response to extracellular pathogens, parasites, are targeted through the TH2 helper cells. 
*'''TH17 Helper Cells:''' These helper cells secrete [[IL-17]] and IL-22. IL-17 affects stromal cells and nearby epithelial cells causing them to secrete cytokines that cause infflammation and attract neutrophils. IL-22 with IL-17 causes epthelial cells to produce antimicrobial peptides to kill bacteria. Therefore, TH17 cells target extracellular pathogens (bacteria and fungi)<ref>Murphy K and Weaver C. Janeway's Immunology. 9th Ed, New York: Garland Science. 2017</ref>. 
*'''Treg Cells: '''A mixed arrangement of cells (including CD4+) which arise in the thymus and suppress other T cell responses as a form of feedback. They secrete suppressive cytokines TGF-B AND IL-10. 
*'''T<sub>FH</sub> Cells: '''CD4+ subset found in B cell follicles of the lymph node. They are specialized to interact with B cells for costimulation. Have different types of responses for different types of infections.

=== References  ===

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