Fibroma regression in relation to antibody and challenge immunity to bovine papilloma virus

Twelve neonate calves were repeatedly challenged with bovine papilloma virus. All calves were initially susceptible to bovine papilloma virus and complete resistance to challenge occurred after the onset of fibroma regression. Fibroma regression was not correlated with serum antibody titers to bovine papilloma virus as measured by an immunodiffusion assay. Fibroma regression occurred prior to the onset of papillomatosis in 8 of the calves. In the 4 calves that had fibroma regression, after the onset of papillomatosis, the fibromas regressed, but fibropapillomas continued to grow progressively.