The PTPN22 1858 T risk allele is associated with increased CD4+ T cells percentage and high mCD154 expression in RA patients, which could favor the pro-inflammatory cytokine release and the establishment of the inflammatory response at the seropositive RA.
A functional variant (R620W) of the intracellular protein tyrosine phosphatase N22 (PTPN22) has now been conclusively shown to confer approximately two-fold risk for seropositive RA as well as several other autoimmune disorders.