The epidermal growth factor-like domain of the human cartilage large aggregating proteoglycan, aggrecan: increased serum concentration in rheumatoid arthritis.

The large aggregating proteoglycan from human cartilage, aggrecan, has recently been shown to possess an immunologically detectable domain with close homology to epidermal growth factor (EGF), that is variably expressed by alternative mRNA splicing. Using a competitive ELISA we detected this domain in sera from both patients with RA and normal controls. The EGF-like domain could only be detected after digestion of sera with chondroitinase ABC, which demonstrates its proteoglycan origin. The concentration of the aggrecan EGF-like domain was considerably elevated in sera from patients with RA as compared to the control sera (P < 0.001), and the concentration of the domain increased with age in both the patient (r = 0.58, P < 0.05) and the control (r = 0.66, P < 0.01) group. These results demonstrate that the EGF-like domain of aggrecan could be of value as a marker of RA.