Regulatory T cells in erythema nodosum leprosum maintain anti-inflammatory function

Area of Science:

• Immunology
• Infectious Diseases
• Cell Biology

Background:

• Regulatory T cells (Tregs) numbers vary in leprosy: increased in lepromatous leprosy (LL) and decreased in erythema nodosum leprosum (ENL).
• The functional capacity of Tregs in LL and ENL remains incompletely understood.

Purpose of the Study:

• To investigate the suppressive function of Tregs in LL and ENL.
• To determine if Treg function is altered in these leprosy complications.

Main Methods:

• A longitudinal study involving LL and ENL participants in Ethiopia.
• Peripheral blood mononuclear cells (PBMCs) were analyzed for TNFα, IFNγ, and IL-10 responses to Mycobacterium leprae (M. leprae) stimulation.
• Treg function was assessed by depleting CD25+ cells (a Treg marker) and observing cytokine responses before and after treatment.

Main Results:

• Depletion of CD25+ cells enhanced TNFα and IFNγ responses to M. leprae, indicating Treg-mediated suppression in LL and ENL.
• Mitogen-induced responses were unaffected by CD25+ cell depletion, suggesting antigen-specific suppression.
• IL-10 responses to M. leprae varied: unaffected in LL, enhanced in untreated ENL, and reduced in treated ENL after CD25+ cell depletion.

Conclusions:

• Treg-mediated suppression in LL is M. leprae antigen-specific and can be reversed by Treg depletion.
• Treg suppressive function in ENL is intact, even with reduced Treg numbers.
• Treg regulation in leprosy may be IL-10 independent, suggesting alternative immune regulation mechanisms.