The functional insufficiency of human CD4+CD25 high T-regulatory cells in allergic asthma is subjected to TNF-alpha modulation

Background:  Natural CD4⁺CD25^highFoxp3⁺ regulatory T (nTreg) cells are important in maintaining immunologic tolerance, but their role in the pathogenesis of allergic asthma is unclear. We studied the function of nTreg cells in allergic asthmatic children and assessed the factors which may relate to the functional insufficiency of nTreg cells.
Methods:  The percentage of CD4⁺CD25^high Treg cells, the expression of Foxp3, and the cell-induced suppressive activity of nTreg cells isolated from nonatopic controls, allergic asthmatics, and allergen-specific immunotherapy (AIT)-treated asthmatic patients were studied.
Results:  Although the percentage of nTreg in peripheral blood mononuclear cells was increased, the expression of Foxp3 and its cell-induced suppressive activity were significantly lower in Dermatophagoides pteronyssinus (Der p)-sensitive asthmatic children when compared to nonatopic controls. In contrast, the expression of Foxp3 and the functional activity of nTreg cells were reversed in allergic asthmatics who received AIT. The addition of recombinant tumor necrosis factor (TNF)-α directly downregulated Foxp3 expression and abrogated the cell-induced suppressive function of Treg cells. The anti-TNF-α reagent, etanercept, restored the functional activity and Foxp3 expression of CD4⁺CD25^high Treg derived from allergic asthmatics.
Conclusions:  The functional insufficiency of nTreg cells in patients with allergic asthma may be related to the enhanced production of TNF-α and its effect on the Foxp3 expression. These results may explain, in part, the effectiveness of anti-TNF-α therapy in the treatment of allergic asthma.