The Interaction between MHC Class II Molecules and Immunogenic Peptides

Abstract

Our immune system performs the crucial task of defending us against attack from microorganisms such as bacteria, parasites, and viruses. To this end the immune system has been endowed with very powerful weapons against foreign, and, to avoid unwanted destruction of the body itself, with the ability to distinguish between “self” and “non-self”. The main players of the immune system are the blood borne lymphocytes, the so-called B and T cells, the only cells known sofar with the capacity to examine and respond to molecules (antigens) in their surroundings. Especially the T cells appear to occupy a central role in regulating the immune system and in distinguishing between self and non-self. Antigen recognition by T cells is unusually complicated. T cells on their own seem to be blind; they require the presence of another cell type, the so-called accessory cell. Among other requirements, the accessory cell must be able to take up and alter antigens (in a function called antigen processing), and subsequently display processed antigen in association with accessory cell synthesized proteins, the major histocompatibility gene complex (MHC) molecules. The MHC genes which encodes for these membrane glycoproteins are the most polymorphic loci known ie. many different alleles exist in the population, however each individual only possesses a few of these. Here, we will deal with some recently gained insights into how T cells recognize antigens. The main emphasis will be on the interaction between MHC class Il molecules and immunogenic peptides, however, we will first introduce antigen processing.