A longitudinal study of the leukocyte protein L1 as an indicator of disease activity in patients with rheumatoid arthritis.

L1 is a major granulocyte and monocyte protein. It is released during leukocyte activation, and the plasma level is thought to reflect the inflammatory activity. Fifteen patients with classical or definite rheumatoid arthritis were examined monthly during one year. The laboratory tests included L1, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), orosomucoid, haptoglobin, ceruloplasmin, alpha 1-antitrypsin, immunoglobulins and blood cell counts. The clinical tests included articular index, grip strength, morning stiffness and pain. The L1 protein was found to have highly significant correlations (p less than 0.0001) with orosomucoid (r = 0.86), CRP (r = 0.79), ESR (r = 0.78), haptoglobin (r = 0.75), alpha 1-antitrypsin (r = 0.63) and ceruloplasmin (r = 0.44). Significant correlation was also found between L1 and IgA. None of the laboratory variables showed significant correlation with pain, but when they were correlated with articular index, grip strength and morning stiffness, L1 was found to have the highest average correlation coefficient (p less than 0.0001).