Figure 4.

Schematic presentation of immune factors in the arthritic process. (a) A healthy joint. The histology of a healthy rhesus monkey diarthrodial joint resembles that of humans, namely, a thin synovium lining the synovial cavity and a rather thick layer of hyaline cartilage covering the articular bone. No marked activity of the bone marrow is observed. (b) The early phase of collagen-induced arthritis (CIA). Synovitis with marked infiltration of T lymphocytes and macrophages is already present in clinically unaffected joints. (c) The late phase of CIA. We have little information about this stage of the disease, because monkeys are usually killed earlier, for welfare reasons.