An autoimmune-associated variant in PTPN2 reveals an impairment of IL-2R signaling in CD4(+) T cells.

The IL-2/IL-2R signaling pathway has an important role in autoimmunity. Several genes identified in genome-wide association (GWA) studies encode proteins in the IL-2/IL-2R signaling cascade that are associated with autoimmune diseases. One of these, PTPN2, encodes a protein tyrosine phosphatase that is highly expressed in T cells and regulates cytokine signaling. An intronic risk allele in PTPN2, rs1893217(C), correlated with decreased IL-2R signaling in CD4(+) T cells as measured by phosphorylation of STAT5 (phosphorylated STAT5 (pSTAT5)). We modeled an additive single nucleotide polymorphism (SNP) genotype, in which each copy of the risk allele conferred a decrease in IL-2R signaling (P=4.4 × 10(-8)). Decreased pSTAT5 impacted IL-2Rß chain signaling resulting in reduced FOXP3 expression in activated cells. This phenotype was not due to overt differences in expression of the IL-2R, molecules in the IL-2R signaling cascade or defects in STAT5. However, the rs1893217(C) risk variant did correlate with decreased PTPN2 expression in CD4(+)CD45RO T cells (P=0.0002). Thus, the PTPN2rs1893217(C) risk allele associated with reduced pSTAT5 in response to IL-2 and reduced PTPN2 expression. Together, these data suggest that decreased expression of PTPN2 may indirectly modulate IL-2 responsiveness. These findings, identified through genotype/phenotype relationships, may lead to identification of novel mechanisms underlying dysregulation of cytokine signaling in autoimmunity.

Insulin gene VNTR genotype associates with frequency and phenotype of the autoimmune response to proinsulin.

Immune responses to autoantigens are in part controlled by deletion of autoreactive cells through genetically regulated selection mechanisms. We have directly analyzed peripheral CD4+ proinsulin (PI) 76-90 (SLQPLALEGSLQKRG)-specific T cells using soluble fluorescent major histocompatibility complex class II tetramers. Subjects with type I diabetes and healthy controls with high levels of peripheral proinsulin-specific T cells were characterized by the presence of a disease-susceptible polymorphism in the insulin variable number of tandem repeats (INS-VNTR) gene. Conversely, subjects with a 'protective' polymorphism in the INS-VNTR gene had nearly undetectable levels of proinsulin tetramer-positive T cells. These results strongly imply a direct relationship between genetic control of autoantigen expression and peripheral autoreactivity, in which proinsulin genotype restricts the quantity and quality of the potential T-cell response. Using a modified tetramer to isolate low-avidity proinsulin-specific T cells from subjects with the susceptible genotype, transcript arrays identified several induced pro-apoptotic genes in the control, but not diabetic subjects, likely representing a second peripheral mechanism for maintenance of tolerance to self antigens.

Different NK cell surface phenotypes defined by the DX9 antibody are due to KIR3DL1 gene polymorphism.

KIR3DL1 and KIR3DL2 are NK cell receptors for polymorphic HLA-B and -A determinants. The proportion of NK cells that bind anti-KIR3DL1-specific Ab DX9 and their level of binding vary between individuals. To determine whether these differences are due to KIR polymorphism, we assessed KIR3D gene diversity in unrelated individuals and families. Both KIR3DL1 and KIR3DL2 are highly polymorphic genes, with KIR3DS1 segregating like an allele of KIR3DL1. A KIR haplotype lacking KIR3DL1 and KIR3DS1 was defined. The two KIR3DL1 alleles of a heterozygous donor were expressed by different, but overlapping, subsets of NK cell clones. Sequence variation in KIR3DL1 and KIR3DL2 appear distinct; recombination is more evident in KIR3DL1, and point mutation is more evident in KIR3DL2. The KIR3DL1 genotype correlates well with levels of DX9 binding by NK cells, but not with the frequency of DX9-binding cells. Different KIR3DL1 alleles determine high, low, and no binding of DX9 Ab. Consequently, heterozygotes for high and low binding KIR3DL1 alleles have distinct subpopulations of NK cells that bind DX9 at high and low levels, giving characteristic bimodal distributions in flow cytometry. The Z27 Ab gave binding patterns similar to those of DX9. Four KIR3DL1 alleles producing high DX9 binding phenotypes were distinguished from four alleles producing low or no binding phenotypes by substitution at one or more of four positions in the encoded protein: 182 and 283 in the extracellular Ig-like domains, 320 in the transmembrane region, and 373 in the cytoplasmic tail.

Killer cell receptors: keeping pace with MHC class I evolution.

NK cells express receptors that bind to polymorphic determinants of MHC class I heavy chains. MHC ligands vary greatly between mammalian species, and the use of distinct molecular families of NK cell receptors by humans and mice suggests that the receptors too can be evolving rapidly. The KIR (killer cell inhibitory receptor) family of receptors are found in primates and recognize class I epitopes that are of relatively recent origin in primate evolution. Therefore, KIR molecules have probably evolved class I receptor function more recently than C-type lectins, which are represented in both humans and mice. Individual humans express NK cell receptors for which they have no class I ligand, demonstrating a looseness in the coupling of expression between the receptors and their ligands. However, study of a single donor suggests that every NK cell expresses at least one inhibitory receptor for a self-HLA class I allotype, consistent with the missing self hypothesis. Thus the NK-cell receptor-class I interaction appears to control the NK-cell repertoire during ontogeny of the individual and has the potential to be a selective factor influencing both MHC class I and NK cell receptor diversity in the evolution of populations and species.

Functionally and structurally distinct NK cell receptor repertoires in the peripheral blood of two human donors.

The expression of KIR and CD94:NKG2 receptors was determined for more than 100 natural killer (NK) cell clones obtained from two blood donors who differ in their HLA class I and KIR genes. More than 98% of the clones were inhibited by individual autologous class I allotypes, and every clone was inhibited by the combination of autologous allotypes. The patterns of inhibition correlate with expression of inhibitory receptors of defined specificity. One donor possesses three class I ligands for KIR, and a majority of NK cells use KIR as their inhibitory receptor; the second donor possesses only a single ligand for KIR, and a majority of NK cells use the more broadly reactive CD94:NKG2a as their inhibitory receptor. Because of these differences, the first donor has subpopulations of NK cells that kill cells of the second donor, whereas the NK cells of the second donor are universally tolerant of cells from the first donor.

Human diversity in killer cell inhibitory receptor genes.

The presence and expression of killer inhibitory receptor (KIR) and CD94:NKG2 genes from 68 donors were analyzed using molecular typing techniques. The genes encoding CD94:NKG2 receptors were present in each person, but KIR gene possession varied. Most individuals expressed inhibitory KIR for the three well-defined HLA-B and -C ligands, but noninhibitory KIR genes were more variable. Twenty different KIR phenotypes were defined. Two groups of KIR haplotypes were distinguished and occurred at relatively even frequency. Group A KIR haplotypes consist of six genes: the main inhibitory KIR, one noninhibitory KIR, and a structurally divergent KIR. Allelic polymorphism within five KIR genes was detected. Group B comprises more noninhibitory KIR genes and contains at least one additional gene not represented in group A. The KIR locus therefore appears to be polygenic and polymorphic within the human population.

The receptor tyrosine kinase-related gene (ryk) demonstrates lineage and stage-specific expression in hematopoietic cells.

We attempted to isolate novel receptor tyrosine kinase, which may play a role in hematopoietic development by screening for expressed sequences with conserved tyrosine kinase catalytic domains. Among the known tyrosine kinases identified in this screen, we found a gene with characteristics of a receptor tyrosine kinase but unusual motifs in the catalytic domain. This gene is identical to ryk described independently by other investigators. Chromosomal fluorescence in situ hybridization localization of human ryk was clarified by using monochromosomal hybrids and placing it as a single locus in 3q22. Although Northern analysis reveals widespread expression in adult mouse tissues, we have found that ryk expression is not ubiquitous. Expression increased in bone marrow cells from mice treated with 5-fluorouracil. Northern analysis on cell lines indicates expression in CD3-, CD4-, CD8- T cells (at a low level), pre-T cells, thymic epithelial cells, and mature myeloid cells, but not myeloid precursors or B cell precursors. Expression analysis with the use of RT-PCR on mouse bone marrow cells separated on the basis of cell surface markers (B220, CD4, CD8, Gr-1, Mac-1) reveals that this receptor is expressed in differentiated cells (Lin+) but is not expressed in the precursor cells (Lin-). Flow cytometric analysis with a monospecific anti-Ryk Ab demonstrates that Ryk+ cells constitute 36.7% and Lin+/Ryk+ cells constitute 33.7% of low density bone marrow cells whereas Ryk+ cells represent only 0.3% of the Lin- population. We conclude that ryk expression is regulated during hematopoietic development by lineage commitment and stage of maturation.