Antibody trapping: A novel mechanism of parasite immune evasion by the trematode Echinostoma caproni

• Published in: PLoS neglected tropical diseases 2017-07, Vol.11 (7), p.e0005773-e0005773
• Main Authors: Cortés, Alba, Sotillo, Javier, Muñoz-Antolí, Carla, Molina-Durán, Javier, Esteban, J Guillermo, Toledo, Rafael
• Format: Article
• Language: English
• Subjects: Analysis; Animals; Antibodies; Antibodies, Helminth - metabolism; Biology; Biology and Life Sciences; Control; Control methods; Countries; Developing countries; Disease control; Disease Models, Animal; Diseases; Drug therapy; Dynamics; Echinostoma - immunology; Echinostoma - isolation & purification; Echinostoma - pathogenicity; Echinostomatidae; Echinostomiasis - parasitology; Electron microscopy; Entrapment; Flukes; Fluorescent antibody technique; Funding; Global health; Growth; Health aspects; Host-parasite interactions; Identification; Immune Evasion; Immunofluorescence; Immunoglobulins; In vitro methods and tests; Infection; Infections; Interactions; Intestine; Labeling; Labelling; LDCs; Male; Marine invertebrates; Medicine and Health Sciences; Mice; Microscopy, Fluorescence; Microscopy, Immunoelectron; Parasites; Protease inhibitors; Protein Binding; Proteinase inhibitors; Proteins; Proteolysis; Research and Analysis Methods; Roles; Secretion; Secretory products; Secretory vesicles; Tegument; Trapping; Tropical climate; Tropical diseases; Ultrastructure; Vaccine development; Vaccines
• ISSN: 1935-2735; 1935-2727; 1935-2735
• DOI: 10.1371/journal.pntd.0005773

Helminth infections are among the most prevalent neglected tropical diseases, causing an enormous impact in global health and the socioeconomic growth of developing countries. In this context, the study of helminth biology, with emphasis on host-parasite interactions, appears as a promising approach for developing new tools to prevent and control these infections. The role that antibody responses have on helminth infections is still not well understood. To go in depth into this issue, work on the intestinal helminth Echinostoma caproni (Trematoda: Echinostomatidae) has been undertaken. Adult parasites were recovered from infected mice and cultured in vitro. Double indirect immunofluorescence at increasing culture times was done to show that in vivo-bound surface antibodies become trapped within a layer of excretory/secretory products that covers the parasite. Entrapped antibodies are then degraded by parasite-derived proteases, since protease inhibitors prevent for antibody loss in culture. Electron microscopy and immunogold-labelling of secreted proteins provide evidence that this mechanism is consistent with tegument dynamics and ultrastructure, hence it is feasible to occur in vivo. Secretory vesicles discharge their content to the outside and released products are deposited over the parasite surface enabling antibody trapping. At the site of infection, both parasite secretion and antibody binding occur simultaneously and constantly. The continuous entrapment of bound antibodies with newly secreted products may serve to minimize the deleterious effects of the antibody-mediated attack. This mechanism of immune evasion may aid to understand the limited effect that antibody responses have in helminth infections, and may contribute to the basis for vaccine development against these highly prevalent diseases.