Evaluation of Serum Levels of IL-17 and IL-22 in Leprosy: A Case-Control Study

BACKGROUND: Leprosy exhibits a wide clinical spectrum that is largely determined by host immune responses. Recent evidence suggests an important role of the Th17/Th22 axis in disease activity and lepra reactions. PRIMARY OBJECTIVE: This study aimed to compare serum interleukin (IL)-17 and IL-22 levels between patients with leprosy and age- and sex-matched healthy controls. SECONDARY OBJECTIVES: This study also aimed (i) to evaluate the variation of serum IL-17 and IL-22 levels across the Ridley-Jopling spectrum of leprosy; (ii) to assess their association with lepra reactional states; and (iii) to explore the relationship of these cytokines with slit-skin smear status and disease duration. METHODS: This cross-sectional case-control study included a total number of 68 patients, with 34 clinically and histopathologically confirmed leprosy patients and 34 age- and sex-matched healthy controls attending Maharishi Markandeshwar Institute of Medical Sciences and Research, a tertiary care centre in North India. Serum IL-17 and IL-22 levels were measured using an enzyme-linked immunosorbent assay. Patients were classified according to the Ridley-Jopling spectrum, and reactional states were analysed separately. RESULTS: Mean serum IL-17 and IL-22 levels were significantly higher in leprosy patients than in controls (p = 0.001 and p < 0.001, respectively). Both cytokines varied significantly across the Ridley-Jopling spectrum (p < 0.001). The highest IL-17 levels were observed in erythema nodosum leprosum and reversal reaction (n = 10 (29.4%)), whereas IL-22 levels were markedly elevated in borderline and reactional forms. IL-22 levels were significantly higher in slit skin smear-negative patients (n = 14 (41.2%)), while IL-17 did not show a significant association with smear status. CONCLUSION: Elevated serum IL-17 and IL-22 levels, particularly in borderline and reactional forms of leprosy, support a contributory role of the Th17/Th22 axis in disease immunopathogenesis and highlight their potential utility as biomarkers of inflammatory activity in lepra reactions.