MACROPHAGE CATHEPSIN-L, A FACTOR IN THE EROSION OF SUBCHONDRAL BONE IN RHEUMATOID-ARTHRITIS

Objective. To test the hypothesis that the proteinase cathepsin L is i nvolved in the subchondral bone lesions found in chronic rheumatoid ar thritis (RA). Methods. The medial tibial plateaus from 4 control cases and 30 patients diagnosed as having end-stage RA were examined immuno chemically for cathepsin L. Results. RA lesions include large groups o f mononuclear cells, many of which are rich in cathepsin L, Since thes e mononuclear cells contained the CD68 glycoprotein and, in the electr on microscope, displayed an irregular cell surface, cytoplasmic vacuol es, lysosomes, and phagosomes, they were identified as belonging to th e macrophage family. The lesions were classified into 2 main patterns, both displaying these cathepsin L-rich cells, which, in at least 1 of the 2, were closely associated with bone degradation. Conclusion. The cathepsin L-rich macrophages are sufficiently numerous to be consider ed a major factor in producing the erosion of subchondral bone found i n chronic RA lesions.