Human lymphocytes were separated into highly purified populations using an immunoadsorbent column technique. It was previously reported that both T and B cells exhibited increased 3H-thymidine incorporation in response to PHA, Con A and pokeweed mitogens, whereas only T cells showed increased incorporation in response to specific antigen. In the present studies, the cellular basis of MIF and mitogenic factor production was studied. Both T and B cells produced MIF in response to antigen. The MIF produced by both T and B cells elutes from Sephadex G-100 columns in the same fraction. Studies using BUdR and light suggest that the T cell which produces MIF is also a proliferating cell, whereas the B cell producing MIF is not. Only T cells produce mitogenic factor in response to antigen. The mitogenic factor produced, however, causes both T and B cell populations to increase 3H-thymidine incorporation. The present studies indicate that antigen induced mitogenic factor production and increased 3H-thymidine incorporation are properties of T cells per se, whereas antigen-induced MIF is made by both T and B cells.

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.

Synovitis was produced in the rabbit knee by repeated intraarticular injection of a preparation of mediators of cellular immunity. The mediators were prepared by incubation of KLH with lymph node cells of animals previously immunized with KLH in Freund's adjuvant. Following three intraarticular injections, a chronic synovitis resulted in which hyperplasia of the lining layer and infiltration of the sublining layer occurred. The cell types in the sublining layer were predominantly histiocytes and fibroblasts. These experiments demonstrate that mediators of cellular immunity may produce a chronic inflammatory reaction when injected repeatedly into normal joints. They indicate that the cellular immune response may play a role in the development of the synovitis of immunologically induced arthritides.

Patients with rheumatoid arthritis (RA), patients with positive tuberculin (PPD) skin-tests and controls were studied. The lymphocytes from these groups were cultured in serum-free medium to obtain cell-free supernatants. These lymphocyte cultures were pre-incubated with the appropriate antigen or reconstituted after removal of the cells. Supernatants from RA lymphocytes stimulated in vitro by IgG induced an inhibition of the leucocyte migration, as well as the supernatants from tuberculin-sensitized lymphocytes. However, supernatants from non-RA lymphocytes or tuberculin-unsensitized lymphocytes did not show such an inhibition. These MIF-like supernatants have been studied by Sephadex G-100 gel filtration. A MIF activity has been found for PPD and IgG supernatants between the chymotrypsinogen (MW 23,000) and the lysozyme (MW 17,000). This seems to agree with the classical region where MIF can be usually isolated.

Previous work suggests that peripheral blood lymphocytes from patients with rheumatoid arthritis have altered reactivity. The purpose of this study has been to observe the behavior of cultures of lymphocytes from patients with rheumatoid arthritis when stimulated with autologous 19S rheumatoid factor and with rabbit serum against autologous IgG fraction. The peripheral blood lymphocytes (PBL) from 15 patients with classical rheumatoid arthritis were obtained by passage of the leukocyte-rich plasma through a polyamide fiber column. The purified lymphocytes were cultured with rheumatoid factor obtained from the same donor through Sephadex G-200 chromatography. In another set of experiments rheumatoid lymphocytes were stimulated with rabbit serum containing antibodies against the IgG fraction of the same patient obtained through DEAE chromatography. After five days the lymphocytes were examined for large cells plus cells in mitosis. A positive response was defined as an increase of 5% or more in the experimental tubes when compared with the cells cultured alone. Ten healthy normal subjects were used also as lymphocyte and serum donors. These lymphocytes were cultured alone and with rabbit serum, anti-autologous IgG. 80% of rheumatoid lymphocytes responded with an average of 37% of enlarging and dividing cells when stimulated by autologous RF. The same pannel of lymphocytes responded only with an average of 14% stimulation when cultured with rabbit serum anti-autologous IgG. The response to the 7S antigammaglobulin factor from rabbit in 7 normal PBL was similar to that of rheumatoid lymphocytes. There was some relation between activity of the RA and lymphocyte response to RF and rabbit antiserum. These results could explain the lymphoid infiltration and hyperplasia of patients with RA and, on the other hand, would support the idea that entrapment of RF by leukocytes ('RA cell') would be a protective mechanism.