SKIN-TEST TO ASSESS IMMUNITY AGAINST COTTONTAIL RABBIT PAPILLOMAVIRUSANTIGENS IN RABBITS WITH PROGRESSING PAPILLOMAS OR AFTER PAPILLOMA REGRESSION

This study analyzed in vivo antiviral cellular immune reactions in the Shope rabbit papilloma - carcinoma model. Antigens studied in experim entally infected domestic rabbits were cottontail rabbit papillomaviru s particles produced with the athymic (nu/nu) mouse xenograft system a nd bacterial fusion proteins containing t e major or minor capsid prot ein. Recall reactions to antigens were tested by classic intracutaneou s tests. Positive reactions had a biphasic course. Histopathology of s kin test biopsy specimens showed infiltrating polymorphonuclear cells during the early stages. Later they were replaced by predominantly per ivascular infiltrates composed of mononuclear cells. Time course of sw elling and infiltrates resembled a delayed-type hypersensitivity react ion. Ten of 11 regressor rabbits (p = 0.00006) and 10 of 20 progressor s (p = 0.009) had positive skin tests with intact and/or denaturated v irus particles and individual capsid proteins also could elicit specif ic skin reactions. Skin reactivity to the cottontail rabbit papillomav irus particles was also greater (p = 0.042) in regressor rabbits (8 of 11) when compared to progressors (7 of 20). Recall reactions remained detectable at post-regression times, ranging from several months up t o more than 2 years. We conclude that specific skin reactions against the cottontail rabbit papillomavirus in infected domestic rabbits exis t, and are strongly positive to intact particles of this papillomaviru s in animals (regressors) clinically free of disease.