Partial Dissociation of Rheumatoid Synovial Fluid Cryoprotein: Micro-Complement Fixation by IgG- or IgG and IgM-Containing Fractions and Denatured Calf Thymus Dan

Complement-fixing cryoproteins from rheumatoid synovial fluid were partially dissociated using preparative ultracentrifugation in a 15% sodium chloride, sorbitol gradient. Heavy-sedimenting fractions retained capacity to fix human complement and contained variable amounts of DNA. Using a modified micro-complement fixation procedure, additional complement fixation was obtained upon addition of denatured calf thymus DNA to fractions containing IgG or mixed IgG and IgM. There was little fixation with native DNA. Interaction of heat-aggregated human γG globulin with denatured DNA under assay conditions failed to give micro-complement fixation in excess of that by γG globulin alone, reducing the likelihood that a nonspecific reaction occurs between denatured DNA and γG globulin aggregates. These findings demonstrated the presence in rheumatoid synovial fluid cryoproteins of immunoglobulin with determinants specific for a site or sites on denatured DNA.