Hypothetical model of differential regulation of Helios^+/− Treg development by monocyte subsets. Interaction of T effector (Teff) with CD16⁻ monocyte subset results in expression of TNF-α, which in turn inhibits Helios⁻ Treg development, whereas T cell–CD16⁺ monocyte interactions trigger IL-12 expression, which inhibits Helios⁺ Treg proliferative responses.