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

Background CD4⁺ CD25^highFoxP3⁺ 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.