Plasma lactoferrin and neutrophil elastase in rheumatoid arthritis and systemic lupus erythematosus.

In order to assess lactoferrin (LF), stored in specific granules of neutrophils, as a marker of inflammation, LF was measured in plasma and serum samples of patients with active rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). In active RA, the median plasma LF level (800 ng/ml) was significantly higher than in normal individuals (220 ng/ml) (P less than 0.00001) and patients with active SLE (235 ng/ml) (P less than 0.00001). Median plasma elastase-proteinase inhibitor complex (EPIC) and C-reactive protein (CRP) levels were also significantly higher in patients with RA than in normal individuals (P less than 0.00001) and active SLE (P less than 0.00001 for both EPIC and CRP). Elevations of LF, EPIC and CRP in RA were independent of rheumatoid factor titres. Plasma lactoferrin in RA correlated significantly with EPIC (Rs = 0.7, P less than 0.0001), CRP (Rx = 0.72, P less than 0.0001) and absolute neutrophil counts (Rs = 0.483, P less than 0.02), but surprisingly not with the Ritchie index, with which CRP showed a weak but significant correlation (Rs = 0.27, P less than 0.05 greater than 0.025). Thus plasma LF and EPIC are markers of inflammation in RA and their levels may reflect release of mediators of inflammation into the joint space and periarticular tissue.