Antigen presentation by major histocompatibility complex class I-B molecules.
Class I-b genes constitute the majority of MHC class I loci. These monomorphic or oligomorphic molecules have been described in many organisms; they are best characterized in the mouse, which contains a substantial number of potentially intact genes. Two main characteristics differentiate class I-b from class I-a molecules: limited polymorphism and lower cell surface expression. These distinguishing features suggest possible generalizations regarding the evolution and function of this class. Additionally, class I-b proteins tend to have shorter cytoplasmic domains or in some cases may be secreted or may substitute a lipid anchor for the transmembrane domain. Some are also expressed in a limited distribution of cells or tissues. At least six mouse MHC class I-b molecules have been shown to present antigens to alpha beta or gamma delta T cells. Recent advances have provided insight into the physiological function of H-2M3a and have defined the natural peptide-binding motif of Qa-2. In addition, significant progress has been made toward better understanding of other class I-b molecules, including Qa-1, TL, HLA-E, HLA-G, and the MHC-unlinked class I molecule CD1. We begin this review, however, by arguing that the dichotomous categorization of MHC genes as class I-a and I-b is conceptually misleading, despite its historical basis and practical usefulness. With these reservations in mind, we then discuss antigen presentation by MHC class I-b molecules with particular attention to their structure, polymorphism, requirements for peptide antigen binding and tissue expression.
Department of Microbiology and Immunology, Baylor College of Medicine, Houston, Texas 77030.
S M
SM
Shawar
J M
JM
Vyas
J R
JR
Rodgers
R R
RR
Rich
D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000502:physiology*; D006183:H-2 Antigens / Q000502:physiology; D006680:HLA Antigens / Q000502:physiology; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000145:classification / Q000235:genetics* / Q000502:physiology*; D006801:Humans; D008969:Molecular Sequence Data; D000097625:HLA-E Antigens
D006183:H-2 Antigens; D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D000097625:HLA-E Antigens