ATRA produced by Lp eosinophils is responsible for conversion of Treg cells.

(A) BP eosinophils were sorted and extracted. ATRA in BP eosinophils were quantified by LC/MS/MS. The acitretin was used as the internal standard for ATRA quantification.

(B) MACS-sorted CD4+CD62L+ T cell from the OT-II mouse were cultured under activating coditions with LP or PB eosinophils as described in Figure 3 in the absence (–) or presence of 1ng/ml TGF-β1, or the RA receptor antagonist LE135 and LE540 (RAi). CD4+Foxp3+ Treg cells differentiation was analyzed by intracellular staining and flow cytometry.