Lymphocytes stimulated by antigen produce a variety of soluble mediators. Our studies involve human leukocyte migration inhibition factor (LMIF), a substance that inhibits the migration of polymorphonuclear leukocytes. We are currently investigating the role of lymphocyte subpopulations involved in the expression of LMIF. A variety of techniques are being used to isolate and characterize this mediator. Successful isolation and characterization of LMIF will permit us to study its biological activity. In addition, work is in progress to use the detection of LMIF to study altered immune responses in disease. IgG is being used as antigen to study patients with rheumatoid arthritis, and studies are being done to assess the specificity of this response.