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Background: Fasciolosis is one of the most important parasitic diseases of livestock. The need for better control strategies gave rise to the identification of various vaccine candidates. The recombinant form of a member of the cysteine protease family, cathepsin L1 of Fasciola hepatica (FhCL1) has been a vaccine target for the past few decades since it has been shown to behave as an immunodominant antigen. However, when FhCL1 was used as vaccine, it has been observed to elicit significant protection in some trials, whereas no protection was provided in others. Methods: In order to improve vaccine development strategy, we conducted a linear B-cell epitope mapping of FhCL1 in sheep vaccinated with FhCL1, FhHDM, FhLAP and FhPrx plus Montanide and with significant reduction of the fluke burden, sheep vaccinated with FhCL1, FhHDM, FhLAP and FhPrx plus aluminium hydroxide and with non-significant reduction of the fluke burden, and in unvaccinated-infected sheep. Results: Our study showed that the pattern and dynamic of peptide recognition varied noticeably between both vaccinated groups, and that the regions 55–63 and 77–84, which are within the propeptide, and regions 102–114 and 265–273 of FhCL1 were specifically recognised only by vaccinated sheep with significant reduction of the fluke burden. In addition, these animals also showed significant production of specific IgG2, whereas none was observed in vaccinated-Aluminium hydroxide and in infected control animals. Conclusions: We have identified 42 residues of FhCL1 that contributed to protective immunity against infection with F. hepatica in sheep. Our results provide indications in relation to key aspects of the immune response. Given the variable outcomes of vaccination trials conducted in ruminants to date, this study adds new insights to improve strategies of vaccine development. [ABSTRACT FROM AUTHOR]

Background: The peritoneal cell populations (PCP) are thought to play a crucial role during the early immune response in Fasciola hepatica infection while newly excysted juveniles (NEJ) are migrating in the peritoneal cavity (PC) towards the liver. In this study, we aimed to determine the immunophenotypes of the PCP and to analyse the dynamics of the recruitment of the PCP during the early and late stage of the infection in sheep infected with F. hepatica. Methods: Thirty-seven sheep were divided into three groups: Group 1 (n = 20) and 2 (n = 10) were challenged with F. hepatica, Group 3 (n = 7) was not infected and remained as uninfected control (UC). After the slaughtering, peritoneal lavages were carried out to isolate peritoneal cell populations at 1, 3, 9 and 18 days post-infection (dpi) for Group 1 and at 14 weeks post-infection (wpi) for Group 2 and 3. Flow cytometry was conducted to assess the dynamics of peritoneal cavity cell populations. Results: TCD4 cells showed a significant decrease at 1 and 18 dpi when compared to UC; no statistical differences were detected for TCD8 and WC1+γδ during the early stage of the infection with respect to the UC. CD14 cells exhibited a decreasing trend, with a significant decrease at 9 and 18 dpi when compared to the UC. The dynamics of MHCII and CD83 cells showed a similar increasing pattern from 3 to 18 dpi. During the chronic stage, both TCD4 and TCD8 cells showed no significant differences when compared to the UC, although a slight but statistically significant higher level of WC1+γδ cells was observed. A lower percentage of antigen-presenting cells (APCs) was detected with respect to the UC. Conclusions: The recruitment of the lymphocytes subsets did not show a significant increase during the course of the infection and only WC1+γδ cells displayed a significant increase at the chronic stage. For the CD14, a decreasing trend was observed during the early stage, which was statistically significant at the chronic stage of the infection. Peritoneal CD83 and MHCII cells developed an increasing trend during the early stage of infection, and showed a significant decrease at the late stage of the infection. [ABSTRACT FROM AUTHOR]