The method by which rheumatoid arthritis causes damage is complicated and is still a somewhat controversial area. Here's what most experts agree on...

What happens is that various white blood cells including polymorphonuclear leukocytes, macrophages, and specific lymphocytes called T cells and B cells become hyperactive and cause inflammation.

This inflammation leads to and is perpetuated by the production of chemical messengers, called cytokines. Cytokines are produced by macrophages, T cells, and B cells. These cytokines cause damage by attracting more inflammatory cells to the area, causing more cytokines to be produced. Cytokines promote the release of destructive enzymes that destroy cartilage and other tissues. The cytokines that seem to play the most important role are tumor necrosis factor (TNF) and Interleukin 1 (IL-1). Many other cytokines and cellular mechanisms are involved and this process is the subject of ongoing research.

As inflammation progresses, the synovium becomes swollen and takes on a life of its own.

At this stage it is called pannus and invades and destroys cartilage, bone, tendons, and ligaments resulting in joint deformity and loss of mobility. Some experts have compared the destructive potential of pannus to a slow-growing malignancy. Synovial inflammation causes joint pain, stiffness, swelling, warmth, and redness.

Rheumatoid arthritis effects are seen not only in the joints but in other organ systems as well including the eye, skin, heart, lungs, and peripheral nerves.