Genetic epistasis between killer immunoglobulin-like receptors and human leukocyte antigens in Kawasaki disease susceptibility.

Kawasaki disease (KD) is a pediatric acute multisystemic vasculitis complicated by development of coronary artery lesions. The breakthrough theory on KD etiopathogenesis points to pathogens/environmental factors triggered by northeastern wind coming from China. Natural Killer cells and T lymphocytes express the inhibitory/activating Killer Immunoglobulin-like Receptors (KIR) to elicit an immune response against pathogens by binding to human leukocyte antigens (HLA) class I epitopes. We first report on the role of KIR/HLA genetic epistasis in a sample of 100 Italian KD children. We genotyped KIR, HLA-A, HLA-B and HLA-C polymorphisms, and compared KD data with those from 270 Italian healthy donors. The HLA-A*11 ligand for KIR2DS2/2DS4/3DL2 was a KD susceptibility marker by itself (odds ratio (OR)=3.85, confidence interval (CI)=1.55-9.53, P=0.004). Although no epistasis between HLA-A*11 and KIR2DS2/S4 emerged, HLA-A*11 also engages KIR3DL2, a framework gene encoding for a pathogen sensor of CpG-oligodeoxynucleotides (CpG-ODN), and KD blood mononuclear cells are actually prone to pathogen CpG-ODN activation in the acute phase. Moreover, carriers of KIR2DS2/HLA-C1 and KIR2DL2/HLA-C1 were more frequent among KD, in keeping with data demonstrating the involvement of these HLA/KIR couples in autoimmune endothelial damage. The highest KD risk factor was observed among carriers of KIR2DL2 and two or more HLA ligands (OR=10.24, CI=1.87-56.28; P=0.007).

Possible KIR-driven genetic pressure on the genesis and maintenance of specific HLA-A,B haplotypes as functional genetic blocks.

The HLA genomic structure underlines the permanence of fixed haplotypes transmitted in blocks as allelic combinations. One of the most discussed concerns is how and why such a strong linkage between HLA alleles has been maintained for so long. We hypothesized a possible KIR-driven pressure in the genesis of specific HLA-A,B haplotypes. Certain HLA-A and -B molecules are ligands for the same KIR receptors through the Bw4 binding motif spanning residues 77-83 in the α1 domain. We analyzed the HLA-A and -B genomic types of 9897 Caucasian people (3533 newborns and 6364 adults) subdividing them according to the presence/absence of the HLA-B Bw4 serological epitope. For each HLA-B Bw4- and Bw6-cross-reactive group, we evaluated the presence/absence of HLA-A ligands for KIR3DL1 (HLA-A*23, HLA-A*24, HLA-A*32) and KIR3DL2 (HLA-A*03, HLA-A*11). The frequency of HLA-A KIR ligands significantly increased moving from the HLA-B Bw4/Bw4 to the HLA-B Bw4/Bw6 and the HLA-B Bw6/Bw6 groups among both newborns and adults (P<0.0001). Here, we suggest that, when the HLA-B KIR-ligand motif is lacking, the HLA-A KIR-ligand might have a vicarious role in controlling the natural killer cell-mediated innate immune response. Basing upon this compensatory function in the engagement of KIR receptors, we hypothesize that specific HLA-A,B ancestral haplotypes were generated.

Cytokine genetic profile in Whipple's disease.

Whipple's disease (WD) is a very rare chronic systemic condition characterised by a Th2/T regulatory (Treg) dysregulated immune response versus Tropheryma whipplei, a bacterium widely diffuse in the environment. To investigate whether this Th2/Treg polarised response has a genetic background, we investigated the Th1, Th2, Th17 and Treg cytokine genetic profile of 133 patients with WD. Thanks to the European Consortium on WD (QLG1-CT-2002-01049), the polymorphism of 13 cytokine genes was analysed in 111 German and 22 Italian patients using the polymerase chain reaction with sequence-specific primers (PCR-SSP) technique. The frequencies of the genotypes, haplotypes and functional phenotypes were compared with those obtained in 201 German and 140 Italian controls. Clinical heterogeneity was also considered. Functionally, WD patients may be considered as low producers of TGF-ß1, having an increased frequency of the genotype TGF-ß1+869C/C,+915C/C [12.3 % vs. 3.81 %, odds ratio (OR) = 4.131, p = 0.0002] and high secretors of IL-4, carrying the genotype IL-4-590T/T (5.34 % vs. 1.17 %, OR = 5.09, p = 0.0096). No significant association was found between cytokine polymorphism and clinical variability. Analogously to the recent cellular findings of a Th2/Treg polarised response, we showed that the cytokine genetic profile of WD patients is skewed toward a Th2 and Treg response. This was similar in both German and Italian populations. However, the significant deviations versus the controls are poorer than that expected on the basis of these recent cellular findings.

Targeting the immunogenetic diseases with the appropriate HLA molecular typing: critical appraisal on 2666 patients typed in one single centre.

We compared the immunogenetic data from 2666 patients affected by HLA-related autoimmune diseases with those from 4389 ethnically matched controls (3157 cord blood donors CBD, 1232 adult bone marrow donors BMD), to verify the appropriateness of HLA typing requests received in the past decade. The frequency of HLA-B∗27 phenotype was 10.50% in 724 ankylosing spondylitis, 16.80% in 125 uveitis (3.41% BMD, 4.24% CBD, P < 0.0001); HLA-B∗51 allele was 15.57% in 212 Behçet's disease (12.91% BMD, 9.88% CBD, P < 0.0001); the HLA-DRB1-rheumatoid arthritis (RA) shared epitope was 13.72% in 554 RA (10.85% BMD, 13.48% CBD, P = 0.016); the carriers of almost one of HLA-DQB1 susceptibility alleles were 84.91% in 795 celiac disease (CD) and 59.37% in 256 insulin-dependent diabetes mellitus (IDDM) (46.06% in 875 CBD, 42.75% in 662 BMD P < 0.0001). Overall, our results show that the HLA marker frequencies were higher in patients than controls, but lower than expected from the literature data (excluding CD and IDDM) and demonstrate that, in complex immunogenetic conditions, a substantial number of genetic analyses are redundant and inappropriate, burdening to the public health costs. For this reason, we suggest the Italian Scientific Society of Immunogenetics to establish guidelines to improve the appropriateness of typing requests.