Figure 3

Effect of methotrexate on expression of PTPN22 splice forms. Investigating a possible effect of methotrexate (MTX) treatment. (a,b) For both cell lines (a) and peripheral blood mononuclear cells (PBMCs) (b), cells were incubated with medium and a range of concentrations of methotrexate for 24 h followed by quantitative PCR measurement of PTPN22 and cytotoxicity analysis (Figure S2 in Additional file 1). The ratio of PTPN22_long and PTPN22_v4 is shown in the graphs with standard error. (c) Boxplots showing the distribution in cohort I of the ratio of PTPN22_long and PTPN22_v4 expression stratified by methotrexate treatment. In cohort I, 23 patients were on methotrexate treatment at the time of sampling.