The complete inventory of receptors encoded by the rat natural killer cell gene complex.

The natural killer cell gene complex (NKC) encodes receptors belonging to the C-type lectin superfamily expressed primarily by NK cells and other leukocytes. In the rat, the chromosomal region that starts with the Nkrp1a locus and ends with the Ly49i8 locus is predicted to contain 67 group V C-type lectin superfamily genes, making it one of the largest congregation of paralogous genes in vertebrates. Based on physical proximity and phylogenetic relationships between these genes, the rat NKC can be divided into four major parts. We have previously reported the cDNA cloning of the majority of the genes belonging to the centromeric Nkrp1/Clr cluster and the two telomeric groups, the Klre1-Klri2 and the Ly49 clusters. Here, we close the gap between the Nkrp1/Clr and the Klre1-Klri2 clusters by presenting the cDNA cloning and transcription patterns of eight genes spanning from Cd69 to Dectin1, including the novel Clec2m gene. The definition, organization, and evolution of the rat NKC are discussed.

Association of arthritis with a gene complex encoding C-type lectin-like receptors.

OBJECTIVE: To identify susceptibility genes in a rat model of rheumatoid arthritis (RA) and to determine whether the corresponding human genes are associated with RA. METHODS: Genes influencing oil-induced arthritis (OIA) were position mapped by comparing the susceptibility of inbred DA rats with that of DA rats carrying alleles derived from the arthritis-resistant PVG strain in chromosomal fragments overlapping the quantitative trait locus Oia2. Sequencing of gene complementary DNA (cDNA) and analysis of gene messenger RNA (mRNA) expression were performed to attempt to clone a causal gene. Associations with human RA were evaluated by genotyping single-nucleotide polymorphisms (SNPs) in the corresponding human genes and by analyzing frequencies of alleles and haplotypes in RA patients and age-, sex-, and area-matched healthy control subjects. RESULTS: Congenic DA rats were resistant to OIA when they carried PVG alleles for the antigen-presenting lectin-like receptor gene complex (APLEC), which encodes immunoregulatory C-type lectin-like receptors. Multiple differences in cDNA sequence and mRNA expression precluded cloning of a single causal gene. Five corresponding human APLEC genes were identified and targeted. The SNP rs1133104 in the dendritic cell immunoreceptor gene (DCIR), and a haplotype including that marker and 4 other SNPs in DCIR and its vicinity showed an indication of allelic association with susceptibility to RA in patients who were negative for antibodies to cyclic citrullinated peptide (anti-CCP), with respective odds ratios of 1.27 (95% confidence interval [95% CI] 1.06-1.52; uncorrected P = 0.0073) and 1.37 (95% CI 1.12-1.67; uncorrected P = 0.0019). Results of permutation testing supported this association of the haplotype with RA. CONCLUSION: Rat APLEC is associated with susceptibility to polyarthritis, and human APLEC and DCIR may be associated with susceptibility to anti-CCP-negative RA.

Molecular cloning of KLRI1 and KLRI2, a novel pair of lectin-like natural killer-cell receptors with opposing signalling motifs.

We here report the molecular cloning of a novel family of killer-cell lectin-like (KLR) receptors in the rat and the mouse, termed KLRI. In both species, there are two members, KLRI1 and KLRI2. While the extracellular lectin-like domains of KLRI1 and KLRI2 are similar [74% (rat) and 83% (mouse) amino acid identity], they differ intracellularly. KLRI1 has two immunoreceptor tyrosine-based inhibition motifs (ITIMs) in the cytoplasmic domain, suggesting an inhibitory function. KLRI2 has no ITIM, but a positively charged lysine residue in the transmembrane region, suggesting association with activating adapter molecules. Klri1 and Klri2 are localized within the natural killer (NK) cell gene complex on rat chromosome 4 and mouse chromosome 6. By RT-PCR and Northern blot analysis KLRI1 and KLRI2 were selectively expressed by NK cells in both rat and mouse. Epitope-tagged expression constructs of rat KLRI1 and rat KLRI2 induced surface expression of a nondisulphide-linked protein of M(r) 36,000/39,000 and M(r) 34,000, respectively.

Identification of lectin-like receptors expressed by antigen presenting cells and neutrophils and their mapping to a novel gene complex.

In an experimental rat model, we recently mapped an arthritis susceptibility locus to the distal part of Chromosome 4 containing genes predicted to encode C-type lectin superfamily (CLSF) receptors. Here we report the cDNA cloning and positional arrangement of these receptor genes, which represent rat orthologues to human Mincle and DCIR and to mouse MCL and Dectin-2, as well as four novel receptors DCIR2, DCIR3, DCIR4 and DCAR1, not previously reported in other species. We furthermore report the cDNA cloning of human Dectin-2 and MCL, and of the mouse orthologues to the novel rat receptors. Similar to the killer-cell lectin-like receptors (KLR) some of these receptors exhibit structural features suggesting that they regulate leukocyte reactivity; e.g., human DCIR and rodent DCIR1 and DCIR2 carry an immunoreceptor tyrosine-based inhibitory motif (ITIM), predicting inhibitory function, and conversely, in all three species Mincle has a positively charged amino acid in the transmembrane region, suggesting activating function. Sequence comparisons show that the receptors form a discrete family, more closely related to group II CLSF receptors than to the group V KLR. Their distance to the KLR is underscored by their preservation of evolutionary conserved calcium/saccharide binding residues, present in group II and lacking in group V CLSF and their cellular expression patterns, with most of the genes preferentially expressed by professional antigen-presenting cells (dendritic cells, macrophages and B cells) and neutrophils. In all three species, the genes map together, forming an evolutionary conserved gene complex, which we call the antigen presenting lectin-like receptor complex (APLEC).

High resolution mapping of an arthritis susceptibility locus on rat chromosome 4, and characterization of regulated phenotypes.

The rat Natural Killer cell gene Complex (NKC) encodes molecules that can regulate immunity. It is located within an interval on DA rat chromosome 4 (RNO4) that is linked to immune-mediated inflammatory joint diseases, including oil-induced arthritis (OIA). We aimed to test the hypothesis that NKC regulates arthritis, by performing advanced mapping of arthritis and additional phenotypes induced by an intradermal injection of incomplete Freund's adjuvant-oil. Reciprocal transfer of RNO4 intervals established that alleles from DA confer arthritis susceptibility to inbred LEW.1AV1 and PVG.1AV1 rats, whereas LEW.1AV1 and PVG.1AV1 alleles confer resistance to inbred DA. Subcongenic strains with PVG.1AV1 alleles introduced on DA allowed mapping of disease predisposition to 0.8 cM on the cytogenetic band 4q42, within the quantitative trait locus oil-induced arthritis-2 (Oia2), but outside the NKC. Alleles in Oia2 regulated arthritis in an additive fashion, and determined arthritis incidence, severity and day of onset, in both males and females. Besides macroscopic joint-inflammation, Oia2 also regulated other oil-induced phenotypes, including lymphoplasia and plasma levels of the inflammation marker alpha1-acid glycoprotein. The high-impact Oia2 region harbors gene sequences similar to human C3AR1, Ribosomal protein L7, DNAJA2, C-type lectins, C1s and CD163. These candidate disease genes may be of general interest, given that rat 4q42, and the syntenic mouse 6F2 and human 12p13 regions are linked to several inflammatory diseases, including rheumatoid arthritis.