Estimation of serum level of interleukin-17 and interleukin-4 in leprosy, towards more understanding of leprosy immunopathogenesis

Background: Combating Mycobacterium leprae is known to be via T-helper1 response. However, other T-helper effector cells; T-helper17 and T-helper2; play a role, particularly in the context of disease type. Aims: We aimed to evaluate serum levels of interleukin (IL)-17 (T-helper17 cytokine) and IL-4 (T-helper2 cytokine) in untreated patients with different types of leprosy, compared to controls. Methods: Using enzyme-linked immunosorbent assay, serum IL-17 and IL-4 levels were estimated in 43 leprotic patients and 43 controls. Patients were divided into six groups; tuberculoid, borderline cases, lepromatous, erythema nodosum leprosum (ENL), type 1 reactional leprosy, and pure neural leprosy. Patients were also categorized according to bacillary load and the presence or absence of reactions. Results: Serum IL-17 was significantly lower in cases (4-61.5 pg/mL; median 19), compared to controls (26-55 pg/mL; median 36) (P < 0.001), and was significantly lower in each type of leprosy compared to controls, with the lowest level in lepromatous leprosy (4-61.5 pg/mL; median 12.5). Significantly elevated serum IL-4 was found in patients (1.31-122.4 pg/mL; median 2.31) compared to controls (1.45-5.72 pg/mL; median 2.02) (P = 0.008), with the highest level among lepromatous leprosy patients (2-87.2 pg/mL; median 28.9), and the lowest in type 1 reactional leprosy (1.4-2.5 pg/mL; median 1.87) (P = 0.006). Conclusion: Defective secretion of IL-17 is related to disease acquisition as well as progression toward lepromatous pole in leprosy patients. The overproduction of IL-4 in patients with lepromatous leprosy may infer their liability to develop ENL. Nevertheless, the small number of the studied population is a limitation.