Although M. wageneri has been reported as being nonpathogenic (2), caryophyllaeid cestodes affect their hosts in three ways: by blocking the intestinal tract, through the production of lesions inducing a marked inflammatory response selleck chemical at their site of attachment

and by disrupting the physiological balance of the host (3,4). The alimentary canal represents one of a few major entry points for pathogens and parasitic infection (5), and that of teleosts, as in other vertebrates, possesses an effective local immune system (6), with well-developed physical and chemical barriers used in combination with an effective mucosal immune system (6). Most protozoan and helminths exert their effects on intestinal tissue either through their CH5424802 datasheet adhesion to it or their penetration through it (7). Parasitic infections can induce several alterations to the host immune response, frequently provoking an inflammatory response resulting in variable numbers and types of leucocytes subsequently being observed in the epithelium and lamina propria of host tissue (5,8–10). Inflammation is a very important mediator of resistance because of its rapid and broad efficacy in clearing infection, and the majority of immune responses begin with the induction and propagation

of inflammation by a series of positive-feedback loops (11). Under normal conditions, fish maintain a healthy state by defending themselves against pathogens, using a complex system of innate defence mechanisms (12). In fish, these innate defences in response to helminth infection are associated with inflammatory reactions (5) that are most frequently elicited by the migrating stages of the parasite (13). Innate immunity is the first line of defence against infection, directing the type of response that the adaptive immune system makes (14,15). The innate

immune system of fish comprises the following: (i) cytotoxic (i.e. natural killer) or phagocytic filipin (i.e. macrophages and granulocytes) cells, (ii) proteins that mediate the responses (e.g. complement) to helminth infection that subsequently initiates the inflammatory response or the release of cytokines to control specific cellular components and (iii) the use of physical and chemical barriers to minimize the likelihood of parasitic infection (e.g. epithelial barriers and antimicrobial peptides) (14). Evidence for the involvement of granulocytes, that is, mast cells (MCs) (16–18) and neutrophils (15,19,20), in the immune system of fish is growing where they have been reported to play a critical role in the defence against pathogens (21,22). MCs, or eosinophilic granule cells (23), which have been reported from all vertebrate groups, commonly occur in the connective tissues of the alimentary canal and the respiratory, urinary, tegumentary and reproductive systems of most fish species (23,24).