Immunologic characterization of serum factors responsible for cold urticaria

Serum factors from 2 patients with primary acquired cold urticaria have been characterised. These serum factors, which can passively transfer cold urticaria to normal recipients, are low in titer, have short skin-fixation times, and are relatively thermostable. Reduction with dithiothreitol or mercaptoethanol followed by alkylation with iodoacetamide destroyed the cold urticaria transfer activity. The passive transfer factor in both cases was recovered in Sephadex G-200 gel filtration fractions that primarily contained IgM immunoglobulins. Cold urticaria transfer activity was obtained in euglobulin fractions produced by dialysis of whole serum against lowionic strength low-pH buffers. While the fractions contained low concentrations of all classes of immunoglobulins, only IgM was present in significant amounts (20 to 40 per cent of whole serum IgM). Cold urticaria passive transfer activity persisted after specific adsorption of IgA, IgG, or IgE from various fractions or whole sera. It was, however, removed after complete adsorption of IgM. These data suggest that the serum factors responsible for cold urticaria in these patients belong to the IgM class. Possible mechanisms for the urtication phenomenon are discussed.