Superantigens

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A superantigen is defined as a type of antigen which has the ability to cause polyclonal T cell activation via a large, nonspecific activation of T cells. There are three general families of superantigens: endogenous superantigens, exogenous superantigens, and B cell superantigens. Endogenous superantigens are encoded into the genome by different viruses; exogenous superantigens simply refer to toxins secreted by bacteria; and B-cell superantigens describe the superantigens which activate B-cells. Superantigens have the unique ability to bind to both T cells, as well as MHC class II molecules (MHC=major histocompatibility complex). Ultimately, the goal is to bring these two types of molecules together so that they can effectively activate even more T cells (“up to 20% of all T cells”) in a non-specific manner due to the superantigen binding to the Variable B region of T cells. Cytokines, which are immune system proteins which are secreted for the purpose of carrying signals amongst cells, are released as a result of this increased activation of T cells and may even induce toxic shock. This Toxic Shock Syndrome is due to Staphlyococcus aureus, characterized by “erythematous eruption and high fever”. An important cytokine molecule, TNF-alpha (tumor necrosis factor alpha), is secreted amongst these cytokines and plays a vital role in the inflammatory response of the body. An over secretion of TNF-alpha may result “endothelial and vascular smooth muscle changes, which manifests as hypotension, shock, and features of sepsis.” An example of a bacterium that elicits a superantigen response in humans is the bacterium Streptococcus pyogenes. The main difference between normal antigen responses and the superantigen response can be seen with different levels of T cell activation. While sapproximately “.001-.0001%” of T cells are activated with a normal antigen response, about 20% of T cells are activated with superantigens. This increased activation is due to the non...
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