CD19 and rheumatoid arthritis: First, MR analysis was conducted on the two immune cells, HLA DR on CD33- HLA DR+ and CD19 on IgD+ CD38- naïve, which were FDR-positive in the MR analysis of immune cells and RA, in relation to the metabolite docosatrienoate (22:3n3) levels, but no significant causal relationship was found.