Summary
The presence of a substance in serum which inhibits the activity of the rheumatoid disease agglutinating factor for sensitized sheep red blood cells is confirmed. It has been shown that this inhibitory substance is present in saline tissue extracts of heart muscle, lung, liver, spleen, kidney and placenta. The evidence indicates that the substance is a heat labile globulin that denatures on exposure to 57°C for 2 hr and that it combines directly with the R.A. factor. Disassociation between inhibitor and factor can be brought about by heat without loss of potency of the latter but with inactivation of the former.
Normal human serum contains large amounts of free inhibitory substance, a considerable quantity of R.A. factor bound to inhibitor and little or no free R.A. factor. Serum from cases of rheumatoid disease contain large amounts of R.A. factor, some factor bound to inhibitor and little or no free inhibitor.
Consideration is given to an hypothesis that R.A. factor is an antibody and inhibitor probably a complex hapten that arises from tissue metabolism and that the hapten can become fully antigenic by the addition of a further component.
