Shunichi Shiozawa

Role of the MICA Polymorphism in Systemic Lupus Erythematosus

OBJECTIVEnTo study the genetic contribution of major histocompatibility complex class I polypeptide-related sequence A (MICA), important in natural killer (NK) cell function, in patients with systemic lupus erythematosus (SLE).nnnMETHODSnJapanese patients with SLE (n=716), those with rheumatoid arthritis (RA) (n=327), and healthy control subjects (n=351) were genotyped for the Val129 Met polymorphism (rs1051792) and transmembrane (TM) alanine-encoding GCT repeats, termed A4, A5, A5.1, A6, and A9, in the MICA gene. Recombinant human MICA-GST fusion proteins were tested on the NK cell line NK92MI for the expression of NK group 2, member D (NKG2-D), NK cell-mediated cytotoxicity, and interferon-γ (IFNγ) production.nnnRESULTSnThe MICA 129Met allele, TMA9 allele, and 129Met/Met genotype were positively associated with SLE (corrected P [Pcorr]=0.01 and odds ratio [OR] 1.3, Pcorr=0.003 and OR 1.6, and Pcorr=0.02 and OR 1.8, respectively), while the MICA 129Val allele was negatively associated with SLE (Pcorr=0.01, OR 0.8). The MICA 129Met;A9 haplotype was also associated with SLE (Pcorr=0.0006, OR 1.8), and there was an additive genetic effect between the MICA 129Met;A9 haplotype and HLA-DRB1*15:01. When NK92MI cells were incubated in vitro with recombinant human disease-associated 129Met;A9 (the combination of polymorphisms at 129Met and TMA9), expression of NKG2-D on NK92MI cells and cytotoxicity of the NK cells were inhibited, but production of IFNγ from NK92MI cells was enhanced.nnnCONCLUSIONnThe MICA polymorphism is genetically associated with SLE, and MICA appears to contribute to the pathogenesis of SLE by modulating NK cell function.

Mixed connective tissue disease is distinct from systemic lupus erythematosus: study of major histocompatibility complex class I polypeptide-related sequence A and HLA gene polymorphisms

In 1972, Sharp et al. proposed a new disease, termed mixed connective tissue disease (MCTD), which is characterized by the presence of autoantibodies against uridine-rich U1 small nuclear ribonucleoprotein (U1 snRNP). There has been some controversy over whether MCTD is truly a distinct disease, as it shares some symptoms with systemic lupus erythematosus (SLE) and others. On the other hand, MCTD patients exhibit an unusually high prevalence of pulmonary hypertension (PH), not commonly observed in SLE, suggesting that MCTD is a distinct disease. We have studied polymorphisms in the major histocompatibility complex (MHC) class I polypeptide-related sequence A (MICA) gene located in the human leukocyte antigen (HLA) locus. Its transmembrane (TM) region in exon 5 is highly polymorphic and can be classified into A4, A5, A5.1, A6, and A9 subtypes, depending on its GCT repeats. There is a single nucleotide polymorphism (SNP) at codon 129 in exon 3 named MICA 129, and the resulting amino acid change Val129Met (rs1051792) modulates the binding of MICA to natural killer receptor group 2, member D (NKG2D), an activating receptor expressed on NK and CD8+ T cells. Clinically, a genetic association exists between the MICA 129Met;A9 haplotype and the susceptibility of Japanese patients to SLE (1). Additive genetic effects also exist between the MICA 129Met;A9 haplotype and HLA-DRB1 *15:01, a known risk allele for SLE in the Japanese population. We obtained genomic DNA from 69 outpatients with MCTD, 209 outpatients with SLE, and 342 healthy controls, with written consent to the respective Institutional Review Boards. These DNAs were analyzed by polymerase chain reaction as described (1). Statistical analyses were performed using the chi-squared test and Fisher’s exact test. The odds ratios (OR) were calculated by Haldane’s modification of Woolf’s method. The association of MICA with HLA-DRB1 polymorphism was tested using the Svejgaard and Ryder’s methods. We observed that the allele frequency of MICA 129Val was significantly increased in MCTD patients as compared with controls and also with SLE patients (P = 0.021, corrected P [P corr] = 0.042, OR = 1.7; 95% confidence interval [95% CI] = 1.1–2.7, and P = 0.000089, P corr = 0.00018, OR = 2.5, 95% CI = 1.5–4.0, respectively). The frequency of the homozygous MICA 129Val/Val genotype was accordingly increased in MCTD patients compared with controls and with SLE patients (P = 0.0098, P corr = 0.029, OR = 2.0, 95% CI = 1.2–3.5 and P = 0.00051, P corr = 0.0015, OR = 2.7, 95% CI = 1.5–4.8, respectively). There was not a significant decrease in the frequency of the heterozygous MICA 129Met/Val genotype in MCTD patients as compared with controls (OR = 0.5 and 95% CI = 0.3–0.9), suggesting that in the Japanese population, MICA 129Val is a recessive trait. The allelic and genotypic frequencies of the MICA TM in MCTD patients were comparable to those of the controls and SLE patients. We also examined the possible association of MICA 129Val with HLA-DRB1 *09:01, a known risk allele for MCTD in the Japanese population (2), and found that MCTD patients with the MICA 129Val/Val genotype also had a significantly increased incidence of the HLA-DRB1 *09:01 allele as compared with controls and with SLE patients (P = 0.00051, P corr = 0.0046, OR = 3.9, 95% CI = 1.8–8.6, and P = 0.00008, P corr = 0.00071, OR = 5.1, 95% CI = 2.2–11.8, respectively) (Table 1). It was reported that among Swedish subjects there is an association of MCTD with the MICA TMA4, HLA-DRB1*04 , and TNF1 haplotypes (OR = 40.6), and also with the homozygous MICA TMA5.1/A5.1 genotype (OR = 3.7) (3). However, we did not observe an association with MICA TMA5.1/5.1 genotype in our study [0 of 69 patients (0%) vs 14 of 342 controls (4.1%); OR = 0.2], presumably because the association between MICA polymorphisms and MCTD varies with race. Instead, we observed that the MICA 129Val/Val genotype is a novel risk factor for MCTD in Japanese subjects. In addition, we confirmed observations by others (2) that