Identification of the complement 9‐binding protein in Setaria equina excretory‐secretory products

Abstract

The current study aimed to detect the complement-binding proteins in the excretory-secretory (ES) products of adult filarial parasite Setaria equina (SeqES). Tests for complement activation pathways (CH 50 and APH 50 ) in normal human serum (NHS) after incubation with SeqES were performed. Quantitative detection of complement activation products like C3d and sC5b-9 by ELISA in inulin-activated NHS before and after addition of SeqES was estimated. Immunoblotting for 1D and 2D electrophoresed SeqES were performed for detection of C9-binding protein. MALDI mass sequencing and multiple sequence alignment were performed for identification of the protein. The results showed an inhibitory effect of SeqES for complement activation pathways. This was confirmed by an obvious reduction in C3d and sC5b-9 in inulin-activated NHS. Immunoblotting showed the reaction of a protein at 21 kDa with human C9. The latter protein was identified as OV-16 based on MALDI mass sequencing and multiple sequence alignment. In conclusion, S equina OV-16 is the complement regulatory protein by its ability to bind C9 and inhibit the classical and alternative pathways of complement activation. This protein can be used as a target for therapeutic treatment or as an anti-inflammatory agent in human diseases. K E Y W O R D SComplement 9, excretory-secretory products, OV-16, Setaria equina

The Secretome of Filarial Nematodes and Its Role in Host-Parasite Interactions and Pathogenicity in Onchocerciasis-Associated Epilepsy

“…The human calreticulin homologue is involved in the regulation of gene expression, cellular Ca 2+ homeostasis, endothelial nitric oxide production, chaperone activity, interaction with protein disulphide isomerase, and acting as a C1q receptor on the surface of phagocytes ( Tsuji et al., 1998 ; Yadav et al., 2014 ). Parasite-derived calreticulin inhibits the complement activation pathway by interacting with the first component C1q of the human complement system ( Tsuji et al., 1998 ; Yadav et al., 2014 ; Abdel-Latif, 2020 ). C1q is the recognition protein of the classical complement activation pathway which normally exists as part of the C1 complex, and Ca 2+ is essential for C1q stability and function.…”

“…This results in a reduction of C3 cleavage as well as soluble C5b-9. Prevention of C3 cleavage prevents opsonisation, phagocytosis, complement-mediated cytolysis and inflammation, whereas binding with C9 inhibits formation of the complement membrane attack complex ( Abdel-Latif, 2020 ). The first is probably the most important for survival of filarial nematodes since C3a is neutrophil chemotactic and stimulates the release of inflammatory mediators from various leukocytes ( Abdel-Latif, 2020 ).…”

“…Prevention of C3 cleavage prevents opsonisation, phagocytosis, complement-mediated cytolysis and inflammation, whereas binding with C9 inhibits formation of the complement membrane attack complex ( Abdel-Latif, 2020 ). The first is probably the most important for survival of filarial nematodes since C3a is neutrophil chemotactic and stimulates the release of inflammatory mediators from various leukocytes ( Abdel-Latif, 2020 ). Furthermore, glyceraldehyde-3-phosphate dehydrogenase has been identified as a C3 binding protein ( Abdel-Latif, 2020 ) and paramyosin was found to bind both C1q and C9 in the roundworm Trichinella spiralis and was also identified in O. volvulus and D. immitis ( Sommer et al., 2001 ; Morchon et al., 2014 ; North et al, 2019 ; Abdel-Latif, 2020 ).…”

“…The first is probably the most important for survival of filarial nematodes since C3a is neutrophil chemotactic and stimulates the release of inflammatory mediators from various leukocytes (Abdel-Latif, 2020). Furthermore, glyceraldehyde-3-phosphate dehydrogenase has been identified as a C3 binding protein (Abdel-Latif, 2020) and paramyosin was found to bind both C1q and C9 in the roundworm Trichinella spiralis and was also identified in O. volvulus and D. immitis (Sommer et al, 2001;Morchon et al, 2014;North et al, 2019;Abdel-Latif, 2020). Human serine protease inhibitors or serpins regulate fundamental processes, including coagulation, complement activation and inflammation.…”