Presence of anti-cyclic citrullinated peptide antibody isotypes in juvenile idiopathic arthritis synovial fluid indicates autoantibody production at the site of inflammation

Results Eleven of 47 (23%) JIA SF samples were positive for the different anti-CCP antibody isotypes. IgM anti-CCP antibodies were positive in 9 JIA patients, including 5 oligoarthritis, 3 IgM RF+ and 1 IgM RFpolyarthritis. IgG antiCCP antibodies were positive in 8 JIA patients, including 4 oligoarthritis, 2 IgM RF+, 1 IgM RFpolyarthritis, and 1 enthesitis-related. Two IgM RF+ polyarthritis patients were positive for IgA anti-CCP antibodies, and also positive for all 3 isotypes. Four JIA patients were positive for 2 anti-CCP antibody isotypes, including 1 IgM RFpolyarthritis patient (IgG and IgM) and 3 oligoarthritis patients (2 IgG and IgM, 1 IgA and IgM). Five JIA patients were positive for 1 anti-CCP antibody isotype, including 3 oligoarthritis (2 IgM, 1 IgG), 1 enthesitis-related (IgG), and 1 IgM RF+ polyarthritis patient (IgM). Three JIA patients were positive for the combined IgA/IgG anti-CCP antibody ELISA, including 2 with IgM RF+ polyarthritis and 1 enthesitis-related. Polyarthritis patients demonstrated significantly higher levels of all anti-CCP antibody isotypes compared to the other JIA subtypes (p<0.05). When only evaluating the IgM RF+ polyarthritis patients against the other subtypes, the levels were even more significantly increased (p<0.05). Serum-matched IgG anti-CCP antibody data was available in 27 JIA patients and 5 healthy controls. All 3 IgM RF+ polyarthritis patients were positive for the IgG anti-CCP antibodies in serum and SF. Two JIA patients who were positive for IgG anti-CCP antibodies in SF had a negative result in serum. Date-matched SF and serum IgM and IgA data was available on 12 JIA patients. More JIA patients were positive for IgA anti-CCP antibodies in serum compared to SF, while SF showed increased positivity for IgM anti-CCP antibodies compared to serum.