Sera of some patients with monoclonal IgG gammapathy have been shown to contain a factor producing long-lasting vascular permeability in guinea pig skin. Skin reactions became positive 2 h after the intradermal injections of the sera and persisted for at least 8 h. Such activity could not be demonstrated in the sera of patients with macroglobulinemia, monoclonal IgA gammapathy, or light chain disease. This activity was associated with IgG but not IgM or IgA fractions of the patientrsquo;s serum. The activity was abolished by heating the serum at 63deg;C for 30 min or by treatment of the serum with ME and MIA. The activity, however, was not influenced by treatments with antihistaminics, trypsin inhibitor, or di-isopropyl-fluorophosphate.
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