MHC III

What is MHC Class III?

Varun Ghosh 

MHC Class III region has the highest gene density but some of the genes are not involved in the immune system.

Since class III genes encode several components of the complement system (i.e. C2, C4a, C4b, Bf), they are responsible for the levels of components of compliment system. 

In addition to components of the complement system MHC III genes code inflammatory cytokines, tumor necrosis factor a and 0 (TNF a and P), two heat shock proteins (HSP) etc. They are not membrane proteins and have no role in Ag presentation. MHC Class III molecules are not structurally related to class I and class II molecules but are important in immune response. 

Complement proteins help to activate and maintain the inflammatory process of an immune response. The heat shock proteins are highly conserved proteins produced by cells at the time of shock including heat shock.

The MHC of humans is now completely sequenced. A consortium of laboratories reports in the 28 October 1999 issue of Nature says that they have determined the sequence of 3,673,800 nucleotides on chromosome 6 that encode the genes of the MHC as well as many other genes involved in immune function. 

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