Host-parasite relationship between congenital Toxoplasma infection and mouse brain: role of small vessels.

Small vessels showing inflammatory cell infiltrates were invariably observed in the vicinity of intact Toxoplasma tissue cysts within the brains of mice congenitally infected with the protozoan. Lymphocytes were observed in intimate contact with the luminal aspect of the endothelium, penetrating into the thickened basal lamina and in the perivascular area, which also contained macrophages and neutrophilic granulocytes. Rarely, lymphocytes were observed attached to the outer membrane of the host neurone which contained a Toxoplasma tissue cyst and within the inflammatory infiltrate associated with a disintegrating cyst. An hypothesis is presented which combines these morphological observations to explain the events associated with tissue cyst associated recrudescence of latent Toxoplasma infection in mouse brain.