How do HLA/MHC alleles cause predispositions to certain diseases

Question

How do dome HLA / MHC alleles inherited by individuals cause predispositions to certain diseases?

Hmm... this is Immunology related

Answer 1

There are different kinds of diseases, and different mechanisms.

A.  Autoimmune diseases - the different alleles somehow act in triggering autoimmunity by presenting peptides to activate the immune system inappropriately.

B.  Infectious diseases and parasites - alleles of immune system genes allow people to combat diseases with different efficiencies, i.e. some people with effective alleles would show no symptoms, while others with ineffectual alleles would get sick.

C.  Inherited diseases - gene mapping has repeatedly linked some inherited diseases to immune system loci, like the HLA/MHC genes, but it is not clear why the linkage occurs.  One example is schizophrenia.