Protein Name

Immunoglobulin M rheumatoid factor Fab complexed with IgG4 Fc


Homo sapiens (human)

Biological Context

Rheumatoid arthritis (RA) is a very painful disease that afflicts a large number of people worldwide. It is characterized by inflammation of membrane tissue that covers joints. When recognized early, effective treatment with drugs can slow down or stop the inflammation. However, when left untreated, inflamed tissue may release enzymes that digest and damage bones. The cause of rheumatoid arthritis is unknown, but the disease itself is an autoimmune disease. The immune system attacks healthy tissue and the disease is chronic. There is no cure and no recovery from the disease, although its effects may be controllable. RA can be identified by the presence of auto-antibodies in body fluids, called rheumatoid factors (RF). Usually the production of antibodies is the response to the presence of antigens in the body, compounds that are recognized by the body as foreign. The interaction between antigens and antibodies is highly specific.

Structure Description


The structure here shows the interaction of a fragment of a human RF antibody, coming from an immunoglobulin molecule called IgM, with another fragment from a human antigen, part of an immunoglobulin molecule called IgG. Usually immunoglobulins are antibodies, being produced by the body in response to the presence of antigens. Here both the antibody and the antigen are part of the body's own immune system. Understanding how these molecules interact may help to design new drugs for treatment of the disease.

Protein Data Bank (PDB)



  • Corper, A.L. Sohi, M.K. Bonagura, V.R. Steinitz, M. Jefferis, R. Feinstein, A. Beale, D. Taussig, M.J. Sutton, B.J.; "Structure of human IgM rheumatoid factor Fab bound to its autoantigen IgG Fc reveals a novel topology of antibody-antigen interaction."; Nature Struct. Biol.; (1997) 4:374-381 PubMed:9145108.


author: Arno Paehler

Japanese version:PDB:1ADQ