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Major histocompatibility complex class III

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A class of major histocompatibility complex wherein unlike class I and II the histocompatibility antigens are non-cell membrane molecules, and encoded by the S region of the major histocompatibility complex


Major histocompatibility complex (acronym: MHC) refers to a cluster of genes that specify for major histocompatibility antigens expressed on the surface of the cell. In essence, epitopes (a fragment of protein that the cell displays on its surface) serve as MHC molecules that the immune cells use to distinguish self from non-self and then immunologically respond accordingly. MHCs are of three classes: MHC class I, MHC class II, and MHC class III.

Major histocompatibility complex class III (MHC class III) is the class of MHC that expresses non-cell membrane molecules. This makes it different from the other two major classes (MHC class I and MHC class II). Both MHC class I and class II express epitopes on the cell surface of antigen-presenting cells. The MHC class III produces non-cell membrane molecules encoded by the S region of the major histocompatibility complex. Another difference is that the class III molecules have physiologic roles. Examples of MHC class III molecules are C2, C4, and B factor of the complement system, TNF-α, LTA, and LTB cytokines, and heat shock proteins.


  • MHC class III

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