Serum Interleukin-38 Depletion in Psoriasis and Its Association with Cytomegalovirus Seropositivity: A Case-Control Study in Baghdad, Iraq

Introduction: Interleukin-38 (IL-38) is an anti-inflammatory cytokine that may restrain psoriatic inflammation. Whether cytomegalovirus (CMV) seropositivity contributes to IL-38 depletion and greater disease severity remains unclear. Aim of this study was to compare serum IL-38 concentrations between patients with psoriasis and healthy controls and assess their associations with CMV serostatus and clinical severity. Methods: This hospital-based case-control study enrolled 45 patients with psoriasis vulgaris and 45 age- and sex-matched healthy controls at Medical City, Baghdad, from January to December 2024. Serum IL-38 was quantified by enzyme-linked immunosorbent assay, CMV immunoglobulin G by chemiluminescence immunoassay, and psoriasis severity by the Psoriasis Area and Severity Index (PASI). Data were analyzed using group comparisons, Pearson correlation, and multiple linear regression. Results: Mean serum IL-38 was lower in patients than controls (37.78 ± 6.15 vs 118.6 ± 25.8 pg/mL; P < 0.001). Among patients, 36 (80.0%) were CMV-seropositive and had lower IL-38 concentrations than seronegative patients (31.2 ± 5.5 vs 64.1 ± 6.8 pg/mL; P < 0.001). IL-38 correlated inversely with PASI (r = −0.72; P < 0.001). CMV seropositivity (β = −0.58; P < 0.001) and PASI (β = −0.35; P = 0.001) were independently associated with lower IL-38, whereas age was not. Conclusion: Reduced IL-38 may represent an immunoregulatory deficit linking CMV seropositivity to greater psoriasis severity. IL-38 and CMV serostatus warrant longitudinal evaluation as complementary markers for risk stratification.