ABSTRACT
Human immunodeficiency virus (HIV) enters cells in vitro via CD4 and a coreceptor. Which of 15 known coreceptors are important in vivo is poorly defined but may be inferred from disease-modifying mutations, as for CCR5. Here two single nucleotide polymorphisms are described in Caucasians in CX3CR1, an HIV coreceptor and leukocyte chemotactic/adhesion receptor for the chemokine fractalkine. HIV-infected patients homozygous for CX3CR1-I249 M280, a variant haplotype affecting two amino acids (isoleucine-249 and methionine-280), progressed to AIDS more rapidly than those with other haplotypes. Functional CX3CR1 analysis showed that fractalkine binding is reduced among patients homozygous for this particular haplotype. Thus, CX3CR1-I249 M280 is a recessive genetic risk factor in HIV/AIDS.
Subject(s)
Acquired Immunodeficiency Syndrome/physiopathology , Chemokines, CX3C , HIV Infections/physiopathology , Polymorphism, Single Nucleotide , Receptors, Cytokine/genetics , Receptors, Cytokine/physiology , Receptors, HIV/genetics , Receptors, HIV/physiology , Acquired Immunodeficiency Syndrome/genetics , Acquired Immunodeficiency Syndrome/virology , CX3C Chemokine Receptor 1 , Case-Control Studies , Chemokine CX3CL1 , Chemokines, CXC/metabolism , Chromosomes, Human, Pair 3 , Cohort Studies , Disease Progression , Genetic Variation , Genotype , HIV/physiology , HIV Infections/genetics , HIV Infections/virology , Haplotypes , Homozygote , Humans , Leukocytes, Mononuclear/metabolism , Linkage Disequilibrium , Membrane Proteins/metabolism , Mutation , Polymorphism, Restriction Fragment Length , Polymorphism, Single-Stranded Conformational , Survival Analysis , White People/geneticsABSTRACT
MIC molecules belong to the immunoglobulin superfamily, are encoded within the MHC region and are recognized by gamma/delta T-cell receptors. In humans, at least two functional genes (MIC-A* and MIC-B*) and two pseudogenes (MIC-C* and MIC-D*) exist. Functional MIC gene copies are characterized by a high degree of polymorphism, while pseudogenes bear several debilitating mutations either in the putative extracellular region or in the transmembrane region of the molecule. In this study we sequenced these segments of MIC genes in seven non-human primates in order to determine whether debilitating mutations were present. All the MIC primate genes studied were highly homologous to their human counterparts, and cystein residues involved in the maintenance of the immunoglobulin-like structure were highly conserved. Furthermore, none of the MIC genes studied contained stop codons in the extracellular or transmembrane segments of the molecule, which suggests that at least one functional gene copy exists in non-human primates. A distinct family of MHC immunoglobulin-like genes was recently identified within the MHC class I region in humans (Bahram et al., 1994; Leelayuwat et al., 1994). Members of this MIC (MHC class I chain related) gene family belong to the immunoglobulin superfamily. Similar to classical class I MHC genes, they are characterized by three distinct extracellular domains (alpha 1-3), a transmembrane (TM) segment and a cytoplasmic segment, each encoded by a separate exon (Bahram et al., 1994; Bahram et al., 1996). Other similarities between MIC genes and classical MHC genes include a high degree of polymorphism (Fodil et al., 1996; Pellet et al., 1997) and recognition by T-cell receptors (Groh et al., 1998). These findings suggest that the putative MIC-A* chain has evolved for a function that is related to, but quite distinct from, that of typical MHC class I chains.
