Immunohistochemical study of the local immune response to Fasciola hepatica in primarily and secondarily infected goats.

The distribution of CD2, CD4, CD8, gamma/delta T-lymphocytes, B-cells and IgG lambda-light chain (lambda-IgG) containing cells were analysed in the inflammatory infiltrate associated to hepatic lesions and gallbladder (HL), and in hepatic lymph nodes (HLN) of goats primarily and secondarily infected with Fasciola hepatica. In the HL, CD2 and CD8 T-cells were more numerous (p=0.01) in secondarily rather than in primarily infected goats, whereas CD4 T-lymphocytes were less numerous than CD8 and showed no significant change in both groups. The ratio CD4/CD8 was 0.66 and 0.39 for primarily and secondarily infected goats, respectively. In contrast, in the HLN, CD4 were more numerous than CD8 T-cells, the ratio CD4/CD8 was 2.0 in control, 1.5 and 1.3 in primary and secondary infections, respectively. Gamma/delta T-lymphocytes were scarce in the HL and moderate in the HLN of both primarily and secondarily infected animals. B-cells (IgM+, lambda-IgG+ or CD79+) varied from scarce or moderate in the HL to abundant in the HLN, where CD79+-cells were mainly located in lymphoid follicles and IgM and IgG in plasma-cells of the medullary cords, suggesting an intense local humoral immune response. However, this response did not prevent the hepatic damage in secondarily infected goats, in which hepatic lesions were more severe than in primarily infected ones.