TNF and rheumatoid arthritis: Strikingly, distinct clustering for RA and OA following batch correction for the 7 different acquiry dates was not only observed at the 0 hour time point (i.e., before stimulation with TNF-α/TGF-β1), but also at all time points after stimulation except for the TGF-Î21 late 12 hour time point (Additional file3: Figure S2).