Characterisation of the lymphoproliferation in rabbits experimentally affected with malignant catarrhal fever.

Malignant catarrhal fever (MCF) in rabbits caused by the three Herpesviruses: alcelaphine herpesvirus-1 (AHV-1), ovine herpesvirus-2 (OHV-2) and hippotragine herpesvirus-1 (HipHV-1) induced hyperplasia of lymphoid tissues and accumulations of mononuclear lymphoid cells in non-lymphoid tissues. However, certain lymph nodes were affected preferentially. The lymphoid cells in non-lymphoid tissues were CD43+ T-cells which showed evidence of in situ multiplication. A more detailed phenotypic analysis of splenocytes and lymph node cells in AHV-1 infected rabbits suggested that the hyperplasia was probably due to the expansion of CD8+ T-cells. On the basis of these data and the observations of other authors, that no or very little viral expression can be detected in lesions of MCF affected animals, we propose that the pathogenesis of MCF results from a dysregulation of a secretory T-cell activator. The variable pathology induced by the three viruses may reflect a quantitative or qualitative differences in this proposed activator.