Our Science – Carrington Website
Mary N. Carrington, Ph.D.
Extensive genetic polymorphism is a primary characteristic of the human major histocompatibility complex (MHC) HLA class I and class II loci, which encode products that present antigenic peptides to T cells, initiating an adaptive immune response and clearance of foreign material. Variation within these loci is concentrated primarily at positions that alter amino acid sequences and determine specificity for foreign peptides. Apart from their role in the acquired immune response, HLA class I molecules participate in innate immunity as ligands for the killer immunoglobulin-like receptors (KIR). KIR molecules are expressed on natural killer (NK) cells, critical components of the innate immune system that are directly involved in the anti-viral/anti-tumor immune response. Upon binding of HLA ligand, KIR molecules regulate cytotoxicity and cytokine production through balanced control of activation and inhibition of NK cells. KIR are expressed on a subset of T cells as well, affirming their role in both innate and adaptive immunity, but they are distinct from other NK cell receptors in that they are exceptionally diverse and rapidly evolving (characteristics they share with the HLA molecules). The HLA and KIR loci are located on different chromosomes (6p and 19q, respectively), so they segregate independently. Thus the presence of genes/alleles encoding corresponding receptor-ligand pairs is necessary for functional activity, but the presence of one without the other has no influence on effector cell activity. Given the extensive diversity of the HLA class I and KIR gene loci and the central role of their interactions in modulating both the innate and adaptive immune response, variation at these loci likely influences the risk of disease pathogenesis; it also indicates the necessity for co-evolution of these two sets of genes in order to maintain an appropriate level of functional interaction that is beneficial to the individual.
The main goal of my laboratory is to understand the genetic basis for resistance or susceptibility to disease conferred by HLA and KIR variants and related loci. Our approach involves direct testing for genetic effects of polymorphic genes within the MHC, as well as functionally relevant combinations of HLA class I alleles and KIR genes, on specific disease outcomes. We have detected novel associations between specific KIR/HLA genotypes that are known to behave as receptor-ligand pairs and disease outcomes to infection (HIV and hepatitis C virus [HCV]), cancer (nasopharyngeal carcinoma [NPC] and cervical neoplasia), autoimmune disease (psoriatic arthritis), and maternal-fetal disease (pre-eclampsia, miscarriage, and fetal growth restriction). Upon identification of genetic variants that associate with a given disease outcome, we are committed to assisting collaborators whose expertise allows direct testing for the functional significance of that genetic finding. These collaborative studies have been exceptionally rewarding, specifically for HIV-1 and HCV disease, in that they explain and confirm the genetic data, and thereby provide solid information for potential use in therapeutic development.
A greater understanding of the evolutionary and molecular genetic characteristics of the MHC and the leukocyte receptor complex (LRC), which includes the KIR gene cluster, is also a key objective of my laboratory. This is an especially important consideration when studying genetic loci composed of multiple homologues that share functional activity, which both the HLA genes and the KIR genes exemplify, because it is a significant aid in identifying the actual disease locus amongst multiple logical candidates. In both the MHC and the KIR gene cluster, we have defined patterns of linkage disequilibrium (LD), studied the effects of meiotic recombination on KIR haplotypes, and identified patterns of association between the unlinked KIR and HLA loci that may have evolved due to selection pressures using population based approaches. These and related studies have informed our disease studies by aiding in the interpretation of the data. They also provide a basic understanding of the genetic, evolutionary, and biological properties of these highly polymorphic immune response loci.
This page was last updated on 5/21/2014.