On the latency period of sensitization: inhibition of passive cutaneous anaphylaxis by a factor in normal rat serum.

Addition of normal rat serum to mouse or rat IgE antibody blocks the passive cutaneous sensitization of rats with either IgE. The inhibition can be obtained with isologous and autologous rat serum. The blocking factor was purified and characterized as a molecule with a MW of 69,000 daltons, a sedimentation rate of 4.5 s and an isoelectric point of pH 4.7. The factor blocks the PCA reaction also at previously sensitized skin sites and seems to act on the secretory phase of mediator release.