CD4 and rheumatoid arthritis: This study showed that although CCR9+CD4+ T cells were increased in the PB of RA patients, the proportion of CCR9+ cells in CD4+ T cells was very low (0.54 - 2.58%), which was consistent with the findings of Zhang et al.[24] They found that normal CD4+ T cells rarely express CCR9, whereas T-cell lineage lymphocytic leukemia CD4+ T cells highly express CCR9.