Objective: Interstitial lung disease (ILD) is a serious complication of SSc. We aimed to identify markers associated with SSc-related ILD.
Methods: RNA was prepared from the peripheral blood mononuclear cells of 14 SSc patients, divided into four different RNA pools according to the presence or absence of ILD and to the treatment, and subjected to microarray analysis. Real-time quantitative PCR was used to confirm the microarray results in 43 SSc patients, 42 autoimmune controls and 10 healthy controls. Genomic DNA samples were collected from 149 patients with SSc (70 in Hokkaido and 79 in Tokyo) who underwent a high-resolution CT for the evaluation of ILD and from 230 healthy controls. Genotyping was performed using sequence-specific primers.
Results: The microarray analysis revealed HLA-DRB5 to be the only gene commonly up-regulated in patients with ILD compared with those without ILD in both comparison groups. High expression levels of HLA-DRB5 in SSc patients with ILD were confirmed by real-time quantitative PCR. The prevalence of HLA-DRB5 gene carriers increased in the SSc patients with ILD relative to those without ILD or to healthy controls in both cohorts. Among the four detected alleles, the HLA-DRB5*01:05 allele was significantly more frequent in SSc patients with ILD than in SSc patients without ILD or in healthy controls. These associations were confirmed in the second cohort.
Conclusion: HLA-DRB5 was highly expressed in PBMCs from patients with SSc-related ILD. The HLA-DRB5*01:05 allele is a risk factor for ILD in patients with SSc.