Relationships between rheumatoid cells in culture.

Rheumatoid synovial fluid macrophages are compatible with synovial membrane fibroblasts in mixed cell culture. They do not appear to have had any immunological experience recognized by homologous rheumatoid blood lymphocytes. The fusion between macrophages which often takes place in cultures of rheumatoid synovial fluid cells seems to be the result of a cell membrane change between contiguous cells rather than to the release of of a 'fusion factor'. Other combinations and manipulations of the rheumatoid cell population may yet prove fruitful in the search for cell-associated phenomena important in the pathogenesis of rheumatoid disease.