Lymphocytes from site of disease indicate probable microbiological etiology of "infective-immune" diseases such as rheumatoid arthritis.

Synovial lymphocytes, from the site of disease, by their response to microbiological antigen stimulation as measured by the [3H]thymidine uptake method, indicate the microbiological causes of reactive arthritis and also oligoarthritis unassociated with enteric or genital symptoms. In the study of the etiology and pathogenesis of rheumatoid arthritis, the application of the same procedures gives an indication that the disease is an immune response to a variety of common infective agents, both viral and bacterial. The demonstration of antigens or nucleic acid of an infective agent at the site of disease, in association with a specific local immune response suggests the pathogenetic importance of the agent. Recent studies of relationships between epitopes of infective agents and MHC gene products suggest several ways in which infective agents can directly cause a disease such as rheumatoid arthritis without any requirement for autoimmune contributions. Because the infective agent may be the primary determining factor and the one most amenable to correction or eradication, the term "infective-immune" is suggested in preference to "autoimmune" for these immune-mediated diseases.