Recent concepts on the pathogenesis of rheumatoid arthritis.

The evidence implicating an immune pathogenesis of the lesions of rheumatoid arthritis is presented under four headings: clinical, histopathological, serological and experimental. This leads to the conclusion that the disease occurs in two phases, an initial phase associated with the presence of an exogenous initiating agent and a chronic, apparently self-prepetuating phase maintained by the presence of an autoanitgen. The microbial nature of the initiating agent is considered and it is concluded that present evidence does not exclude the possibility that no single agent is responsible.