Autoimmunity against YKL-39, a human cartilage derived protein, in patients with osteoarthritis.
OBJECTIVE
Our previous study revealed that some patients with rheumatoid arthritis (RA) possessed autoantibodies to YKL-39, a cartilage related protein. We investigated whether patients with osteoarthritis (OA) also displayed autoimmunity to YKL-39.


METHODS
Autoantibodies to recombinant YKL-39 as well as human cartilage glycoprotein-39 were detected by ELISA and Western blotting. The tested serum samples were derived from 117 patients with OA, 94 patients with RA, and 2 groups of 50 arthropathy-free healthy donors who matched the OA and RA groups for age and sex. We determined autoepitopes on YKL-39 using 3 overlapping fragments of YKL-39 (designated F1, F2, F3). T cell proliferation response to YKL-39 was analyzed using the 3H-thymidine incorporation assay.


RESULTS
Autoantibodies to YKL-39 were detected in 13 (11.1%) patients with OA and 11 (11.8%) with RA. In the epitope mapping, all the 3 fragments of YKL-39 were found to carry autoepitopes, but F1 was recognized most frequently. Proliferative responses of peripheral blood mononuclear cells against YKL-39 were detected in 6 (46%) of the 13 OA patients who were positive for the anti-YKL-39 autoantibodies and in 2 (17%) of the 11 antibody positive RA patients.


CONCLUSIONS
These results show that autoimmunity to YKL-39 in patients with OA was present at equal or somewhat higher frequency than in patients with RA. The cellular and humoral immune responses to YKL-39 may be involved in the pathological process of OA as well as RA.
Rheumatology, Immunology and Genetics Program, Institute of Medical Science, St Marianna University School of Medicine, Kawasaki, Japan.
Jun-Ichiro
J
Tsuruha
Kayo
K
Masuko-Hongo
Tomohiro
T
Kato
Masahiro
M
Sakata
Hiroshi
H
Nakamura
Taichi
T
Sekine
Masaharu
M
Takigawa
Kusuki
K
Nishioka
D054392:Adipokines; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000917:Antibody Formation / Q000502:physiology; D001323:Autoantibodies / Q000032:analysis*; D015551:Autoimmunity / Q000502:physiology*; D001483:Base Sequence; D015153:Blotting, Western; D002358:Cartilage, Articular / Q000276:immunology / Q000378:metabolism; D000071451:Chitinase-3-Like Protein 1; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006023:Glycoproteins / Q000276:immunology*; D006801:Humans; D007111:Immunity, Cellular / Q000502:physiology; D037102:Lectins; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D010003:Osteoarthritis / Q000276:immunology* / Q000503:physiopathology; D016133:Polymerase Chain Reaction / Q000379:methods; D012016:Reference Values; D012680:Sensitivity and Specificity
D054392:Adipokines; D001323:Autoantibodies; C084533:CHI3L1 protein, human; D000071451:Chitinase-3-Like Protein 1; D006023:Glycoproteins; D037102:Lectins