Presentation and stimulation capacity of thymic stromal subsets. Proliferative responses of naive OT-I (A) or gBT-I (B) TcR transgenic T cells stimulated by purified thymic stromal cells coated with various concentrations of cognate peptide. Limiting numbers of cTECs restricted their analysis to only certain peptide concentrations within each experiment; however, similar results were obtained throughout. (C) PCR analysis of costimulatory molecules, MHC II, aire, and chemokine transcripts in purified stromal cell subsets. (D) Histograms of H-2D^b, IA^b, CD40, and CD80 expression by thymic stromal subsets (solid line indicates cTECs, mTEC^hi subset [except for IA^b plot], and DCs; dashed line, mTEC^lo (except for IA^b plot); dotted lines, isotype controls). Markers are set to compare expression levels in positive populations. (E) Quantitative PCR analysis of aire transcript levels in purified thymic stromal cell subsets normalized for GAPDH expression. Means and SD generated from 3 different cDNA templates for each population are shown relative to whole TSCs.