Quantification of APRIL production and secretion in healthy and rheumatoid arthritis synovium. Quantification of the Aprily-2 staining (left y axis) and the number of Stalk-1-stained cells (right y axis) for normal synovial tissues (n = 4), for non-rheumatoid arthritis (RA) lesions (n = 7) and for RA lesions (n = 11). Arbitrary units are used for Aprily-2 quantification. Number of stalk-1-stained cells shown for an adjacent area of 30 mm2. Mean values are indicated. *RA lesions with germinal centers and plasma cells. **Seronegative RA lesions. APRIL, A proliferation-inducing ligand.