ZAP70 and rheumatoid arthritis: The aim of the study was to test the hypothesis that a different distribution of circulating memory B cells, plasmablasts and B cell activated subsets (i.e. CD19+/ZAP-70+ B cells) in early compared to long-standing RA could lead to a more favorable clinical response to treatment, and to evaluate whether the distribution of B cell subpopulations correlates with disease activity, particularly with the inflammatory milieu, at the onset of the disease.