Secreted cathepsin L-like peptidases are involved in the degradation of trapped antibodies on the surface of Echinostoma caproni
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Antibody trapping is a recently described strategy for immune evasion observed in the intestinal trematode Echinostoma caproni, which may aid to avoiding the host humoral response, thus facilitating parasite survival in the presence of high levels of local-specific antibodies. Parasite-derived peptidases carry out the degradation of trapped antibodies, being essential for this mechanism. Herein, we show that cathepsin-like cysteine endopeptidases are active in the excretory/secretory products (ESPs) of E. caproni and play an important role in the context of antibody trapping. Cysteine endopeptidase activity was detected in the ESPs of E. caproni adults. The affinity probe DCG-04 distinguished a cysteine peptidase band in ESPs, which was specifically recognized by an anti-cathepsin L heterologous antibody. The same antibody localized this protein in the gut and syncytial tegument of adult worms. Studies with cultured parasites showed that in vivo-bound antibodies are removed from the parasite surface in the absence of peptidase inhibitors, while addition of cathepsin L inhibitor prevented their degradation. These results indicate that cathepsin L-like peptidases are involved in the degradation of surface-trapped antibodies and suggest that cysteine peptidases are not only crucial for tissue-invading trematodes, but they can be equally relevant at the parasite-host interface in gut-dwelling flukes.
KeywordsEchinostoma caproni Trematode Cathepsin Cysteine peptidase Antibody Immune evasion
Research at Universitat de València was supported by Ministerio de Economía y Competitividad (Madrid, Spain) (grant number: BFU2016-75639-P); Conselleria d’Educació, Generalitat Valenciana (Valencia, Spain) (grant number: PROMETEO2014-083 Fase II); and from Ministerio de Sanidad y Consumo (Madrid, Spain) (No. RD12/0018/0013, Red de Investigación Cooperativa en Enfermedades Tropicales—RICET, IV National Program of I+D+I 2008-2011, ISCIII—Subdirección General de Redes y Centros de Investigación Cooperativa and FEDER). Research of PH and LM (Charles University) is currently supported by European Regional Development Fund and Ministry of Education, Youth and Sports of the Czech Republic (CZ.02.1.01/0.0/0.0/16_019/0000759) and Institutional Grants (Charles University PROGRES Q43 and UNCE/SCI/012-204072/2018). We would like to express our sincere gratitude to Professor John P. Dalton, Medical Biology Centre, School of Biological Sciences, Queen’s University Belfast and Dr. Martin Kašný, Department of Parasitology, Faculty of Science, Charles University (Prague), and Department of Botany and Zoology, Faculty of Science, Masaryk University (Brno) for kindly providing some of the antibodies employed in this study.
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Conflict of interest
The authors declare that they have no conflict of interest.
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