Studies on Sensitization. I. Skin Sensitivity and Serum Precipitin Response Following Intracutaneous Injections. ∗

Abstract

This report is the first of a series undertaken with the aim of throwing light on the role of sensitization in infection and immunity. Our early studies deal with the tissue hypersensitiveness that results from repeated injections of protein substances in animals, a condition generally classed under the Arthus phenomenon. Albino rabbits served as the experimental animals and the sensitizing injections were madfe, in most instances, intracutaneously. 1 The white skin in these animals rendered the effects of the injections readily discernible. This fact, in turn, permitted quantitative studies of the skin (local) response and its ready correlation with the serum (general) response.

The present study utilizes the method for measuring skin sensitivity recently reported. 2 Briefly, into the hair-clipped skin of an albino rabbit are injected 0.1 cc. quantities of a series of dilutions of some protein with physiological salt solution. The dilutions usually employed are: undiluted, 1:10, 1:100, 1:1,000, 1:10,000, and 1:100,000. The skin response is read 24 hours after the intracutaneous injections, and the highest dilution producing an inflammatory area, is termed the skin sensitivity titer of the rabbit.

If, for example, human serum previously heated for 30 minutes at 56°C. is used as the protein, the skin of a normal rabbit will show practically no response to this sensitivity test; only the area wherein the undiluted serum had been injected will show a slight transitory edema. A rabbit previously sensitized to human serum, however, will be likely to show, after a similar sensitivity test, a marked inflammatory response with central necrosis in the area where the 0.1 cc. of undiluted serum had been injected; a somewhat less marked response in the area where the 0.1 cc. of the 1:10 serum dilution had been injected, with gradual reduction in the response corresponding to the higher dilutions of serum, showing perhaps only a small erythematous area in the 1 :10,000 dilution, with no response in the 1 :100,000 dilution.