MAJOR HISTOCOMPATIBILITY ANTIGENS: AN INTRODUCTION

Specific immunity depends on the gene products encoded within the major histocompatibility complex (MHC). As the name suggests, the MHC was first identified as a group of genetic loci which influenced the type of immunological responses which followed tissue transplantation. Over 20 years ago, the involvement of MHC molecules in the interaction between B and T cells was demonstrated to be specific and restricted.1–3 As it turns out, the products of two families of MHC encoded genes, termed class I and class II, are the primary molecules used by the immune system to educate immune cells (not to recognize self) and subsequently to activate the entire system following recognition of foreign matter. MHC class I and class II molecules are highly polymorphic membrane expressed proteins which function by binding peptides and “presenting” them to T cells. The last two decades have witnessed a wealth of discovery on MHC molecules and antigen presentation in general, yet more and more detail continues to be uncovered. This chapter is intended to review some of the hallmark observations made in the last five years and to prepare those newly interested in immunology for the more detailed chapters that follow.