Response of Mouse Liver to Infection with Tetrathyridia of Mesocestoides (Cestoda)

Tetrathyridia of Mesocestoides were injected intraperitoneally into a large group of mice. Mice were autopsied sequentially to study the progression of pathological lesions. Focal, then diffuse acute inflammation and anoxic hepatocyte necrosis occurred, followed by repair accompanied by massive parenchymal regeneration. Parasite encapsulation was delayed until regeneration had begun. At this time, eosinophils and plasma cells first appeared. In old infections hepatolobular architecture was lost, and there was portal lymphatic obstruction and ascites. These lesions were related to the migratory behavior of tetrathyridia, to the subsequent return of many to the coelom, and to the delayed appearance of specific host resistance. The interaction between tetrathyridia and liver is compared to that of other hepatic parasites. During the study of the asexual multiplication of Mesocestoides tetrathyridia by Specht and Voge (1965) several different gross lesions in the livers of mice were noted. The purpose of this paper is to report the microscopic composition of these lesions, to show progressive changes in their composition as correlated with duration of infection, and to demonstrate how they are dependent on parasite growth and migratory behavior. MATERIALS AND METHODS Swiss albino mice were injected intraperitoneally with 60 tetrathyridia each in 0.85% NaCl containing 500 units penicillin and 500 ,tg streptomycin per milliliter. Tetrathyridia were obtained from the stock infections in mice (Specht and Voge, 1965). Beginning with 2 days postinfection, 1 or 2 mice were examined every 24 hr through 10 days postinfection. From 10 days through 44 days, 1 mouse was examined every 3 days. From 44 days through 65 days, 1 mouse was examined every 7 days. Three mice were included which were selected at random from stock infections of longer duration (188 days, 365 days, and 455 days postinfection). These had received variable numbers of tetrathyridia. Mice were killed by hyperanesthesia; the abdomen was immediately opened Received for publication 28 December 1971. * USPHS General Research Support Grant 5 SO1 FR-5352-04. t Present address: Department of Pathology, Jackson Memorial Hospital, 1700 N.W. 10th Avenue, Miami, Florida 33136. + All correspondence pertaining to this paper and requests for reprints should be sent to Elmer A. Widmer. and the liver was dissected free and washed in 0.85% NaCl. Gross observations were recorded. The liver was selectively sliced so that different pieces contained variable numbers of lesions. Tissues were routinely fixed in 10% formalin, Bouin's, and Zenker's fluids. Carnoy's fluid was used in selected cases. Specimens were embedded in paraplast, sectioned at 7 p, and stained with hematoxylin and eosin, Mallory's trichrome, P.A.S., Masson's trichrome, or Feulgen following the procedures given by Lillie (1965).