Identification of the ability of a test item to induce an immediate (Type I) hypersensitivity reaction.
Guinea pigs can be sensitized by intramuscular injection of the test item and positive control (i.e. OVA). The immune system may respond by producing antibody to the test item, including (but not limited to) IgE. Some of this circulating IgE will be fixed onto mast cells in various tissues, including the vasculature and respiratory tract. Three weeks later, the same animals are challenged with an intravenous dose of the test item. Following IV injection, the animals potentially develop rapidly a severe vascular shock and die within a few minutes.
The ability to carry out an anaphylactic reaction can be transferred from a sensitive animal to a normal one by transferring serum. Serum is collected from a guinea pig sensitized to test item and positive control (as described above), and a small amount is injected intradermally into a naive recipient animal. After 24 hours (the latent period required for the IgE antibodies to bind to the surface of local mast cells), test item resp. positive control together with the dye Evans Blue is injected intravenously. Within minutes, a blue patch becomes visible on the animal's skin where the immune serum had been injected due to local degranulation of the mast cells that results in capillary dilation, and the leakage of fluids from blood.
Lethality in IHR respective the appearance of the blue patch in PCA indicate a high risk of the test item to induce potential immediate hypersensitivity reactions.