Taenia taeniaeformis: evasion of complement-mediated lysis by early larval stages following activation of the alternative pathway.
Activation of the alternative pathway of complement by T. taeniaeformis oncospheres and early stage metacestodes, although a factor in host defense against primary infection, does not directly lead to the killing of the parasite larvae observed prior to day 6 post-infection in innately resistant BALB/cByJ inbred mice. Immunogold labelling techniques clearly demonstrated tegument-associated C3 on in vitro-activated oncospheres incubated with non-immune mouse sera. However, C5, a protease necessary for the assembly of the membrane attack complex, was not detected. Early stage larvae cultured from in vitro-activated oncospheres escaped membrane damage and survived incubation in non-immune sera from both BALB/cByJ and taeniid-susceptible C3H/HeDub mice. Comparisons of cobra venom factor-treated and untreated C5-deficient B10.D2osn mice revealed no significant differences in parasite burden and local eosinophil infiltration at 6 days post-infection, suggesting that the terminal arm of the complement system is necessary for the previously reported role of complement in resistance to primary infection in BALB/cByJ and C3H/HeDub mice. An in vivo test of chemotaxis indicated that although both complement-intact mouse strains examined responded to intraperitoneal injections of inulin, there were lower numbers of eosinophils in C3H/HeDub mice than in BALB/cByJ mice, perhaps pointing to possible mouse strain differences in C5a generation/catabolism or eosinophil ability to respond to C5a. Lectin-binding studies showed an affinity of PNA for the exposed surface of taeniid oncospheres and 4-day post-infection metacestodes; however, binding of lectin to the carbohydrate moiety did not inhibit complement activation.
Davis
S W
SW
Department of Microbiology, Pathology and Parasitology, North Carolina State University, College of Veterinary Medicine, Raleigh 27606.
Hammerberg
B
B
D000818:Animals; D003176:Complement C3 / Q000032:analysis*; D003182:Complement C5 / Q000032:analysis; D003170:Complement Pathway, Alternative; D005260:Female; D007150:Immunohistochemistry; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D013621:Taenia / Q000276:immunology*; D013622:Taeniasis / Q000276:immunology*
D003176:Complement C3; D003182:Complement C5