Increased concentrations of lipid peroxidation products have been described in the serum and synovial fluid from patients with rheumatoid arthritis. A large proportion of the unsaturated lipids in human extracellular fluids is a component of low density lipoprotein (LDL). The oxidative modification of LDL, and its subsequent uptake by macrophages, has been implicated in the pathogenesis of atherosclerosis, but not of rheumatoid arthritis. This study aimed to assess whether oxidatively modified LDL was present in the rheumatoid synovium.
A polyclonal antiserum raised in rabbits against oxidised LDL (o-LDL) was used to perform an immunohistochemical study of a series of synovial biopsy specimens from patients with rheumatoid arthritis.
Collections of positively stained macrophages, arranged in a linear fashion and with the morphological characteristics of foam cells--that is, 'fatty streaks', were identified around blood vessels within the intimal connective tissue. In addition, scattered, positively stained foam cells were present in association with deposits of fibrin. These staining patterns were absent from control synovial membranes (traumatic knee injuries).
The findings in all rheumatoid patients studied suggest that atherosclerosis and rheumatoid arthritis have analogous pathogenetic features.