Immunohistochemical study of the local immune response in lambs experimentally infected with Dicrocoelium dendriticum (Digenea)

Phenotypic expression of inflammatory cells in liver and hepatic lymph nodes (HLN) has been examined in lambs experimentally infected with Dicrocoelium dendriticum using immunohistochemical techniques. Thirty-two lambs, 12 infected with 1,000 D. dendriticum metacercariae, 12 with 3,000, and 8 controls were used. Half the lambs in each group were slaughtered on days 60 and 180 post-infection (p.i.), respectively. Primary antibodies (Abs) against T cell epitopes (CD3+, CD4+, CD8+ and WC1+ gamma delta), B cell epitopes (CD79 alpha cy+, CD45R+), immunoglobulin (IgG)-bearing plasma cells, macrophages (CD14+, VPM32+) and major histocompatibility complex (MHC) class II beta antigen were used. T lymphocytes (CD3+, CD4+ and CD8+) and B lymphocytes (CD79 alpha cy+ and CD45R+) with diffuse pattern or forming lymphoid aggregates and follicles surrounded the septal bile ducts (SBD) and inter-lobular bile ducts, whereas the WC1 gamma delta T cells were scattered. Numerous IgG+ plasma cells were observed around SBD. CD14 and VPM32+ macrophages intermingled with lymphocytes were immunostained by the anti-MHC class II beta. This Ab also reacted with lymphoid cells. Likewise, increased positive immunostaining for all Abs used was observed in the HLN of infected lambs. There was no qualitative difference regarding the phenotype expression of inflammatory cells between the lambs infected with D. dendriticum. The humoral and cell-mediated local immune responses observed were similar in the two groups of lambs infected with different doses.