Uncoupling of proliferation and cytokines from suppression within the CD4+CD25+Foxp3+ T-cell compartment in the 1st year of human type 1 diabetes.

OBJECTIVE: The mechanistic basis for the breakdown of T-cell tolerance in type 1 diabetes is unclear and could result from a gain of effector function and/or loss of regulatory function. In humans, the CD4+CD25+Foxp3+ T-cell compartment contains both effector and regulatory T cells, and it is not known how their relative proportions vary in disease states. RESEARCH DESIGN AND METHODS: We performed a longitudinal study of CD4+CD25+ T-cell function in children with type 1 diabetes at onset and throughout the 1st year of disease. Function was assessed using single-cell assays of proliferation, cytokine production, and suppression. Type 1 diabetic individuals were compared with age-matched control subjects, and suppression was directly assessed by coculture with control T-cell targets. RESULTS: We identify novel functional changes within the type 1 diabetes CD4+CD25+ compartment. Type 1 diabetic CD4+CD25+ cells exhibited a striking increase in proliferative capacity in coculture with CD4 T cells that was present at onset and stable 9-12 months from diagnosis. Elevated type 1 diabetes CD4+CD25+ cell proliferation correlated with increased inflammatory cytokines interleukin 17 and tumor necrosis factor-α but not γ-interferon. Type 1 diabetes CD4+CD25+ cytokine production occurred coincident with suppression of the same cytokines in the control targets. Indeed, enhanced proliferation/cytokines by CD4+CD25+ cells was uncoupled from their suppressive ability. Longitudinally, we observed a transient defect in type 1 diabetes CD4+CD25+ suppression that unexpectedly correlated with measures of improved metabolic function. CONCLUSIONS: Type 1 diabetes onset, and its subsequent remission period, is associated with two independent functional changes within the CD4+CD25+ T-cell compartment: a stable increase in effector function and a transient decrease in regulatory T-cell suppression.

Regulation of immunity at tissue sites of inflammation.

The acquisition and execution of CD4 effector function are tightly regulated and spatially compartmentalized. In the lymph node (LN), naïve CD4+ T cells acquire specialized functions by means of expression of distinct cytokines and acquire distinct homing properties. Therefore, both the function and subsequent localization of effector cells appears to be predetermined during differentiation in the LN. Our studies with the protozoa Leishmania major suggest that this centrally (LN) generated effector repertoire can be further edited at the infected tissue site. Cytokine production in the inflamed tissue can be modulated at a number of levels including chemokine-driven differential recruitment of effector cells, the provision of signals for effector cell function and suppression by regulatory T cells (Tregs). The concept that tissue resident pathogens may subvert the centrally generated cytokine repertoire has important therapeutic implications. Novel therapies that focus on manipulating the local infection site to encourage appropriate recruitment or activation of effectors may be particularly beneficial.