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The Immune System -- An Overview

October 2008

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The Immune Response

An immune response to foreign antigen requires the presence of an antigen-presenting cell (APC), (usually either a macrophage or dendritic cell) in combination with a B cell or T cell. When an APC presents an antigen on its cell surface to a B cell, the B cell is signalled to proliferate and produce antibodies that specifically bind to that antigen. If the antibodies bind to antigens on bacteria or parasites it acts as a signal for pmns or macrophages to engulf (phagocytose) and kill them. Another important function of antibodies is to initiate the "complement destruction cascade." When antibodies bind to cells or bacteria, serum proteins called complement bind to the immobilized antibodies and destroy the bacteria by creating holes in them. Antibodies can also signal natural killer cells and macrophages to kill viral or bacterial-infected cells.

If the APC presents the antigen to T cells, the T cells become activated. Activated T cells proliferate and become secretory in the case of CD4+ T cells, or, if they are CD8+ T cells, they become activated to kill target cells that specifically express the antigen presented by the APC. The production of antibodies and the activity of CD8+ killer T cells are highly regulated by the CD4+ helper T cell subset. The CD4+ T cells provide growth factors or signals to these cells that signal them to proliferate and function more efficiently. This multitude of interleukins or cytokines that are produced and secreted by CD4+ T cells are often crucial to ensure the activation of natural killer cells, macrophages, CD8+ T cells, and PMNs is listed in the chart below.


References:

  1. Roitt I, Brostoff J, and Male D. Immunology (second edition). J.B. Lippincott Co., 1989.
  2. AMFAR, AIDS/HIV Treatment Directory, Vol 6 No 4, July 1993.
  3. Mosmann TR, Coffman RL. 1989. TH1 and TH2 cells: Different patterns of lymphokine secretion lead to different functional properties. Annual Review of Immunology 7; 145-173.
  4. Yarchoan R, Mitsuya H, and Broder S. 1993. Challenges in the therapy of HIV infection. Immunology Today 14: 303-309.
  5. Wood R, et al. 1993. Safety and efficacy of polyethylene glycolmodified interleukin-2 and zidovudine in human immunodeficiency virus type 1 infection: a phase I/II study. J of Inf Dis 167: 519-525.
  6. Francis ML, Meltzer MS, and Gendelman HE. 1992. Interferons in the persistence, pathogenesis, and treatment of HIV infection. AIDS Res Human Retroviruses 9: 199-207.
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This article was provided by Seattle Treatment Education Project.
 
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