Circulating CD4+ CD25 high FoxP3+ T cells vary in different clinical forms of leprosy.

Background: CD4(+) CD25(high) FoxP3(+) regulatory T cells (T-regs) were reported to increase in chronic infections. We aimed at studying their frequency in leprosy to investigate their role during Mycobacterium leprae infection.

Methods: Using flow cytometry, the frequency and FoxP3 expression of circulating T-regs was assessed in 38 leprosy patients and 38 healthy controls. Patients were divided into; group I tuberculoid (TT), group II borderline cases [borderline tuberculoid (BT), borderline (BB), and borderline lepromatous (BL)], group III lepromatous (LL), and group IV erythema nodosum leprosum (ENL).

Results: Mean T-regs% and FoxP3 expression were significantly elevated in patients (particularly TT) compared to controls (3.8 ± 2.5% vs. 2.5 ± 0.8% and 78.8 ± 56.2% vs. 55.8 ± 15.7%, respectively) (P < 0.05). Comparing the four disease groups, T-regs% was significantly different (median 5.3% in group I, 3.4% in group II, 2.8% in group III, and 1.2% in group IV; P = 0.005). FoxP3% on T-regs was not significantly different between them [median 71.5% in TT, 62.3% in borderline categories, 67.75% in LL, and 85.75% in ENL; P = 0.149). Notably FoxP3 expression was significantly higher in ENL than controls (P = 0.011).

Conclusion: The frequency and suppressive marker of circulating T-regs are elevated in TT patients. Patients with LL and ENL express significantly lower frequency of T-regs and higher FoxP3 expression (in ENL), consistent with disease progression and immune hyper-activation in these disease categories. Thus, rather than being detrimental to immunity, intact T-regs activity may be beneficial to leprosy patients.