from Part I - Recognition of bacteria
Published online by Cambridge University Press: 13 August 2009
INTRODUCTION
Until recently, it was generally believed that proteins encoded within the MHC (or major histocompatibility complex) locus carry out the majority of the immunologically relevant antigen presentation functions necessary to alert the immune system to pathogenic or oncogenic challenges. This notion was initially based on the identification of the MHC as the critical genetic locus involved in tissue graft rejection. Genetic and immunological studies identified the protein products of two distinct families of genes called MHC I and MHC II as being responsible for graft rejection. Additional studies demonstrated that the primary role of these proteins is to signal the immune system to respond to invading pathogens through the presentation of peptide fragments derived from endogenous and exogenous protein sources to different classes of T lymphocytes. Thus, two distinct pathways of peptide antigen presentation for the detection of invading intracellular and extracellular pathogens (or pathogens which reside in intracellular vacuoles) by MHC I and MHC II, respectively, were identified and investigated. The role of the key cell population, the dendritic cell, in antigen presentation has been described in Chapter 1. In the past ten years, however, a new paradigm in immunology has emerged whereby nonpeptide lipid antigens are presented to T cells by the MHC-related protein, CD1.
EVOLUTION OF CD1
The human CD1 (hCD1) polypeptides are members of a family of glycoproteins that are conserved throughout mammalian evolution and were initially identified as thymocyte differentiation antigens (Porcelli and Modlin, 1999).
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