Abstract
Beagle dogs inoculated intravenously with 1.75 x 10(9) viable Encephalitozoon cuniculi spores at 12.5 months of age were monitored for 18 months to assess infection in the adult dog. Parameters monitored included packed cell volume, total and differential leukocyte counts, and humoral and cellular responses to infection. Immunoglobulin M and G antibodies directed against the parasite tegument were present throughout the 18 months. Peripheral blood monocytes treated with lymphokines, either antigen specific (E. cuniculi) or nonspecific (concanavalin A), killed E. cuniculi spores in vitro. Pretreatment of E. cuniculi spores with normal dog serum or infected dog serum enhanced the killing of the parasite (normal dog serum less than infected dog serum) by canine monocytes. Histologic examination of selected tissues revealed microfocal plasma cell and lymphocyte aggregates at the renal corticomedullary junction and in the medullary interstitium. The results of these experiments suggest that the adult dog is able to mount an effective defense to infection, to minimize host tissue damage, and to eliminate the parasite through complex interactions between monocytes-macrophages and lymphocytes.