LEUKOCYTE PROLIFERATION IN-VITRO AGAINST COTTONTAIL RABBIT PAPILLOMAVIRUS IN RABBITS WITH PERSISTING PAPILLOMAS CANCER OR AFTER REGRESSION

Leukocyte proliferation responses to cottontail rabbit papillomavirus (CRPV) were measured in vitro with fresh whole blood as well as with a mmonium chloride lysis-separated leukocytes. The antigens used were (1 ) CRPV particles produced in the athymic (nu/nu) mouse xenograft syste m and (2) purified bacterial fusion proteins of the CRPV major and min or capsid proteins L1 and L2. CRPV-infected domestic rabbits with pers istent papillomas or after papilloma regression, as well as uninfected controls were studied. There was a clearcut difference between infect ed and uninfected animals. We demonstrated antigen-specific leukocyte proliferation to at least one CRPV antigen in 12 of 21 infected rabbit s but there was no positivity in 9 control animals (P = 0.004). There was whole-blood reactivity preferentially to intact CRPV particles in regressors, Specific but weak leukocyte proliferation against CRPV par ticles was detected in 6 of 9 regressor rabbits (66%) but only in 1 of 12 progressors (8%; P = 0.0158). This trend of greater reactivity to intact CRPV particles in regressors as compared with progressors was n ot seen with peripheral blood leukocytes isolated by ammonium chloride lysis. We conclude that specific leukoproliferative responses against capsid CRPV proteins exist in rabbits experimentally infected with CR PV.