Using mass spectrometry-based label free quantitative proteomics analysis of in vitro differentiated murine Th17 and induced T regulatory (iTreg) cells. More than 4000 proteins covering almost all subcellular compartments were detected. Quantitative comparison of the protein expression profiles resulted in the identification of proteins specifically expressed in the Th17 and iTreg cells. Importantly, our combined analysis of proteome and gene expression data revealed protein expression changes that were not associated with changes at the transcriptional level.