Type IX collagen immunoreactive peptides in synovial fluids from arthritispatients

Objectives. To determine whether type IX collagen-related peptides can be d etected in the synovial fluids of arthritis patients and to assess their po tential as molecular markers of arthritis. Patients/methods. Synovial fluids from a set of carefully diagnosed arthrit is patients and from healthy volunteers were used. Hydroxyproline assays we re carried out to determine the content and concentration of collagen. Coll agen cross-link determinations were conducted by reversed-phase HPLC. SDS-P AGE and immunoblotting were used to identify the collagenous components, an d N-terminal sequencing was performed to confirm these identities. Results. All the synovial fluids were found to contain measurable amounts o f collagen at similar concentrations. This appeared to be mainly high-molec ular-weight material consisting of type I and type IX collagens, but not ty pe II collagen. However, other smaller molecular weight type IX immunoreact ive peptides were detected which were more apparent in the synovial fluids from arthritis patients. These peptides were also found to contain noncolla genous material. Collagen cross-links were also present in the arthritis sy novial fluids. Conclusion. Collagenous material can be detected in all synovial fluids and the presence of pyridinoline cross-links indicates that at least some of t his is derived from a mature collagen matrix. Type IX immunoreactive peptid es were identified,but were found to contain significant amounts of non-col lagenous material? and their presence, even at lower levels, in synovial fl uids from normal subjects limits their potential for use as molecular marke rs of disease. Nevertheless, this is the first report of type TX collagen-r elated fragments in synovial fluids.