GPI and arthritic joint disease: By tracking the anti-GPI B cell response in different anatomic sites at different stages of the disease (preclinical, acute, and chronic), the authors could demonstrate, in parallel with arthritis onset and appearance of serum autoantibodies, the localization of anti-GPI+ B cells (and differentiation of anti-GPI secreting B cells) within GCs and medullary cords of peripheral reactive LNs.