Early acute depletion of lymphocytes in calicivirus-infected adult rabbits.

Rabbit Haemorrhagic Disease (RHD) is a lethal infection caused by calicivirus that kills 90% of the infected adult rabbits within 3 days. The calicivirus replicates in the liver and causes a fulminant hepatitis. Most studies on the pathology of RHD have been focused on the fulminant liver disease. This may not be the only mechanism in the pathogenesis of RHD: calicivirus infection may also induce leukopenia in the infected adult rabbits. We show now by flow cytometry analysis that the calicivirus induces an early decrease in B and T cells, in both spleen and liver. The depletion of B and T cells was associated with apoptosis labelled by annexin V. These changes occurred in rabbits before they showed enzymatic evidence of liver damage and persisted after liver transaminase values were very high. We conclude that depletion of lymphocytes caused by the calicivirus infection precedes or attends liver damage. The relative contribution of this lymphocyte depletion for the pathogenesis of the fatal calicivirus infection of rabbits remains to be investigated.