The origin of rheumatoid arthritis (RA) is in our opinion a bacterial infection. The infection gives rise to changes in the macrophages, with release of enzymes, etc., and secondarily abnormal immune processes occur. In favor of this opinion is, among other things, the similarity with rheumatic fever, which is caused by streptococci group A, as well as experience gained in connection with experimentally provoked arthritis
In experimental arthritis, produced by streptococci group B (Svartz), there appears in rats the same type of joint disease as in human RA and, besides, a rheumatoid factor (RF)-like macroglobulin, which cannot be distinguished by available methods from human RF macroglobulin. A 7 S hemagglutinating RF (RF II) was also produced in animals, as well as some other immunoglobulins. The RF II has a much weaker hemagglutinating capacity than the usual RF macroglobulin which for comparison could be termed RF I. The streptococci B used in our investigations were mostly isolated from the nasopharynx of RA patients.