Unlocking the role of the B7-H4 polymorphism in psoriasis: Insights into methotrexate treatment outcomes: A prospective cohort study

B7-H4 is a recently discovered member of B7 family that negatively regulates T-cell immunity, specifically Th1 and Th17 cell responses. However, its role in the pathogenesis of psoriasis has yet to be determined. This study aims to investigate the effect of B7-H4 polymorphism on the efficacy of methotrexate (MTX) and its mechanism in psoriasis. Four single nucleotide polymorphisms of B7-H4 were genotyped in 310 psoriatic patients who received 12-week MTX. The protein expression of B7-H4 in platelets was characterized using immunofluorescence staining, confocal laser scanning microscopy, and flow cytometry techniques. We found that GG genotype carriers of B7-H4 rs1935780 had a lower Psoriasis Area and Severity Index (PASI) 75 response rate and higher weight (p = 0.0245) and body mass index (p = 0.0185) than AA and AG genotype carriers. Multiple regression analysis showed that the PASI score at baseline (p = 0.01) and age at disease onset (p = 0.003) were positively correlated with PASI 75 response rate, while weight (p = 0.005) and the rs1935780 genotype (p = 0.003) were negatively associated with PASI 75 response rate. B7-H4 was expressed in the platelet plasma membrane and cytoplasm. Furthermore, the expression of B7-H4 protein in platelets was lower in good responders than in non-responders and was upregulated considerably after 12-week MTX or in vitro MTX stimulation in good responders. Collectively, these results demonstrate that psoriatic patients with GG genotype of B7-H4 rs1935780 had a poorer response to MTX. Low expression of B7-H4 protein in platelets correlated with better clinical outcomes of MTX in psoriasis.