HLA and the Immune Response

T lymphocytes may be separated into two major functional subpopulations having either regulatory or effector function. Regulatory cells represent about 70% of all T lymphocytes in the peripheral circulation and are separated into helper cells and suppressor cells. The remaining T cells have an effector function and are known as cytotoxic cells. 

A classic paper by Zinkernagel and Doherty in 1974 (Zl) showed that in order for T cells to recognize a foreign antigen, the antigen has to be presented by cells displaying the MHC antigens of the host. The phenomenon became known as MHC restriction.  

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