Antikeratin antibodies inserum andsynovial fluid showspecificity forrheumatoid arthritis inastudy of connective tissue diseases

(IF) on ratoesophagus substrate. Theincidence ofAKA was significantly raised inrheumatoid arthritis (37%)incomparison withsystemic sclerosis (8%),psoriasis (7%),ankylosing spondylitis (6%),systemic lupus erythematosus (3%), andnormalcontrols (2%).AKA were detected insynovial fluid obtained frompatients with rheumatoid arthritis (RA)(48%)butnotfrompatients withotherconditions. Further experiments on AKA-positive serashowedreactivity withstratum corneum ofrabbit prepuce andlips. A specific rabbit antihuman keratin antiserum was shown, byIFandinhibition studies, tohavea different specificity fromthatofspontaneous humanAKA. AKA wereassociated withthepresenceofsubcutaneous nodules inRA (p=0.05), butnotwith Raynaud's phenomenon, Sjogren's syndrome, orHLA-DR4positivity. Rheumatoid factor (RF) was notassociated withAKA either inRA or inRF-positive disease controls.