Canine Distemper Virus: Review of Structural and Functional Modulations in Lymphoid Tissues

Abstract

SUMMARY A review is made of the morphologic and functional aspects of canine distemper-virus ( cdv ) infection on lymphoid tissues. Fatal infection is associated with virus-related systemic depletion of T and B lymphocyte-dependent areas in lymphoid tissues. Massive lymphoid necrosis, a feature of infection in conventional animals, does not occur with cdv infection in gnotobiotes. Additional lesions seen are focal and then diffuse reticulum cell hyperplasia, occasionally virus-associated syncytial giant cells, and intracytoplasmic viral inclusion bodies. In subacutely affected or convalescent dogs, repopulation of lymphoid tissues with associated germinal center formation commences 16 to 20 days after infection. Germinal center formation in the medullary portion of the thymus may be present as a residual lesion in these animals. Infection results in a leukocyte-associated viremia and viral strain-dependent lymphopenia of both B and T cells which may persist long into convalescence. Accompanying this alteration is loss of in vitro lymphocyte responses to phytomitogens. In vitro and in vivo cellular responses to test antigens are transiently suppressed in actively infected and in vaccinated challenge exposed animals. Outcome of infection is correlated with prompt development of cdv -specific humoral and cellular immunity. Dogs surviving cdv infection are less able to make antibodies to an immunogen than are noninfected controls. The results of these studies indicate that cdv has profound immediate and long-term effects on normal lymphoid tissue structure and function in dogs.