In rheumatoid arthritis, “arthr-“ refers to joints, “-itis” means inflammation, and “rheumatoid” comes from rheumatism, which more broadly refers to a musculoskeletal illness.
So, rheumatoid arthritis is a chronic, inflammatory disorder that mostly affects the joints, but can also involve other organ systems like the skin and lungs as well.
Alright, so a healthy joint typically has two bones covered with articular cartilage at the ends.
Articular cartilage is a type of connective tissue that acts like a protective cushion - a lubricated surface for bones to smoothly glide against.
One type of joint, like the knee joint is called a synovial joint.
A synovial joint connects two bones with a fibrous joint capsule that is continuous with the periosteum or outer layer of both bones.
The fibrous capsule is lined with a synovial membrane that has cells that produce synovial fluid and remove debris.
The synovial fluid is normally a viscous fluid like the jelly-like part of a chicken egg and it helps lubricate the joint.
To help serve these synovial cells, the synovial membrane also has blood vessels and lymphatics running through it.
Together, the synovial membrane and the articular cartilage form the inner lining of the joint space.
Rheumatoid arthritis is an autoimmune process that is typically triggered by an interaction between a genetic factor and the environment.
For example, a person with a certain gene for an immune protein like human leukocyte antigen, or HLA- DR1 and HLA–DR4, might develop rheumatoid arthritis after getting exposed to something in the environment like cigarette smoke or a specific pathogen like a bacteria that lives in the intestines.
These environmental factors can cause modification of our own antigens, such as IgG antibodies or other proteins like type II collagen or vimentin.
Τype II collagen and vimentin can get modified through a process called citrullination.