Immunopathological Response, Histological Changes, Parasitic Burden, and Egg Output in Sheep Naturally Infected by Dicrocoelium dendriticum

Abstract

The aim of this study was to investigate the correlation between infection by Dicrocoelium dendriticum (class Trematoda) and the animal host response in terms of macroscopic lesions, the immunopathological response, and histological changes in the livers of naturally infected sheep. Twenty-four sheep were selected on the basis of positive D. dendriticum fecal egg counts (FECs). Gross and histological injuries were scored. A positive significant association was observed between the number of adult worms recovered from the liver, FEC, macroscopic lesions, fibrosis, and bile duct hyperplasia. A significant negative association was observed among these variables and the degree of leukocyte infiltration. In addition, immunophenotyping of the inflammatory cells was carried out using primary antibodies against T cell epitopes (CD3+, CD4+, and CD8+), B cell epitopes (CD79α), and the ionized calcium-binding adapter molecule 1 (IBA-1) antigen. Independently of the severity of the D. dendriticum infection, the predominant cell population was CD3-positive and associated with lesser numbers of CD79α- and Iba-I-positive cells. An increase in Iba-1-positive cells was observed in the livers of animals with a high worm burden. Our results provide a reference basis to better understand the local immune response in sheep naturally infected by D. dendriticum in relation to the FEC and parasitic burden.

Keywords: Dicrocoelium dendriticum; FLOTAC; fibrosis; leucocytic inflammation; sheep.

Figure 1

Representative sections from the liver tissues of sheep (a): Liver section from sheep of Group A (<30 egg per gram (EPG)) showing mild fibrosis and severe leukocyte infiltration; (b): liver section from sheep of Group B showing moderate fibrosis and leukocyte infiltration around the bile ducts; (c): liver section from sheep of the Group C showing severe fibrosis around the bile ducts and mild leukocyte infiltration. Masson’s trichrome (original magnification 100×).

Figure 2

Liver (a): Lymphoid aggregate composed of CD79-positive cells associated with a moderate number of CD-79-positive lymphocytes around the hyperplastic bile duct (liver from Group A); (b): CD3-positive cells in the periphery of the lymphoid aggregate (liver from Group B); (c): CD3+ cells scattered diffusely around the hyperplastic bile ducts (liver from Group C); (d): a moderate number of CD8+ cells around the bile ducts (liver from Group A); (e): a moderate number of CD4+ cells around hyperplastic bile ducts (liver from Group B) (immunohistochemistry, HRP method, original magnification 200×); (f): a moderate number of ionized calcium-binding adapter molecule 1 (IBA-1)-positive cells scattered around the bile ducts and within follicular aggregates (liver from Group A) (immunohistochemistry, HRP method, original magnification 100×).