Thoracic duct cannulation and hemal node formation in mice infected with cowpox virus.

Mice experiencing generalized and fatal infection after i.v. injection of large doses of cowpox virus showed no significant changes in the recirculating pool of thoracic duct lymphocytes. There was little or no growth of virus in lymphoid tissues, but changes associated with the immune response and with stress (mediated by corticosteroid hormones) were substantial. A characteristic feature of fatal cowpox virus infection was the formation of hemal nodes accompanied by the appearance of large numbers of erythrocytes in the thoracic duct lymph from the 3rd day after inoculation. Erythrocytes entered lymphatics to form hemal nodes after extravasation from small blood vessels. Extravasation resulted from vascular damage caused by the growth of virus in vessel walls.