CD27 and IL-35 as diagnostic biomarkers in alopecia areata: First evidence of association with pathogenic scalp bacterial infections

Objective: This study aimed to investigate the diagnostic and prognostic potential of CD27 and interleukin-35 (IL-35) in patients with Alopecia Areata (AA), with and without pathogenic bacterial infections. To our knowledge, this is the first study to correlate CD27 and IL-35 expression with bacterial colonisation in AA. Methods: A total of 60 patients with clinically diagnosed AA and 60 age- and sex-matched healthy controls were recruited. Blood samples were analysed for CD27 and IL-35 using ELISA. Scalp swabs from AA patients were cultured on blood agar, MacConkey agar, and Mannitol salt agar; bacterial isolates were identified through biochemical assays and confirmed by the VITEK 2 Compact System. Bacteria were deemed pathogenic if colony-forming unit concentrations exceeded 10³–10⁴ CFU/mL. Statistical analysis included ANOVA, Pearson correlation, and ROC curve analysis. Results: Among AA patients, 43.3% showed bacterial growth; 12 isolates were classified as pathogenic. The most common species were Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa, and Staphylococcus haemolyticus. CD27 and IL-35 levels were significantly elevated in AA patients with bacterial infections compared to those without bacterial infections and to healthy controls (p = 0.001). A strong positive correlation was observed between CD27 and IL-35 in infected patients (r = 0.742). CD27 showed perfect diagnostic performance (AUC=1.00), while IL-35 was a strong predictor in infected cases (AUC = 0.94). Conclusion: CD27 and IL-35 may serve as useful immunological biomarkers in AA. Elevated IL-35 levels appear to be driven by bacterial-induced immune activation, suggesting a potential role for combined immunomodulatory and antimicrobial therapies.