MCAM and rheumatoid arthritis: Functional heterogeneity explains why there was no significant correlation between CD146+ CD4 cell frequencies and Th17 frequencies in either HDs or in RA patients' blood (P > 0·05 each; Supporting information, Fig. S3a,b) – the presence of other effector cell populations within the CD146+ population and the lack of CD146 expression on many Th17 cells would confound any such correlation.