Mononuclear cells derived from bone marrow, synovium and peripheral bl
ood of patients with rheumatoid arthritis (RA) were examined for their
capacity to produce rheumatoid factor (RF) in order to investigate th
e origin of circulating RF. The results demonstrate that mononuclear c
ells derived from bone marrow are able to produce IgG-, IgA- and IgM-R
F and that the amounts of RF produced by bone marrow cells are not sig
nificantly different from that by dissociated synovial cells. Since ci
rculating immunoglobulins are mainly derived from the bone marrow this
observation suggests that also RF circulating in RA patients mainly o
riginates from the bone marrow.