Figure 4. CD16 bioactivity in synovial fluid versus serum in patients with arthritis. (A) Graphic experimental design. Paired serum and synovial fluid samples were sampled and used to determine CD16 activation indices in these liquids using the reporter cell model. (B) Comparison of paired serum and synovial fluid samples from patient with seropositive rheumatoid arthritis (RA, n=3, left) and control diseases (n=7 patients without RA (non-RA) with joint effusions including two patients with psoriasis arthritis and each one patient with reactive arthritis, juvenile idiopathic arthritis, spondyloarthritis and immune-related adverse event arthritis). The graphs show mean and SD of interleukin (IL)-2 concentration produced by CD16+ reporter cells in serial dilution experiments. Serum and synovial fluid from non-RA control diseases did not lead to statistically different CD16 activation, while two-way repeated measures analysis of variance confirmed significant differences between RA serum and RA synovial fluid (p=0.035) and also between dilution steps (p=0.007).