Cathepsins B1 and B2 of Trichobilharzia SPP., Bird Schistosomes Causing Cercarial Dermatitis

Abstract

Trichobilharzia regenti and T. szidati are schistosomes that infect birds. although T. regenti/T. szidati can only complete their life cycle in specific bird hosts (waterfowl), their larvae-cercariae are able to penetrate, transform and then migrate as schistosomula in nonspecific hosts (e.g., mouse, man). Peptidases are among the key molecules produced by these schistosomes that enable parasite invasion and survival within the host and include cysteine peptidases such as cathepsins B1 and B2. These enzymes are indispensable bio-catalysts in a number of basal biological processes and host-parasite interactions, e.g., tissue invasion/migration, nutrition and immune evasion. Similar biochemical and functional characteristics were observed for cathepsins B1 and B2 in bird schistosomes (T. regenti, T. szidati) and also for their homologs in human schistosomes (Schistosoma mansoni, S. japonicum). Therefore, data obtained in the research of bird schistosomes can also be exploited for the control of human schistosomes such as the search for targets of novel chemotherapeutic drugs and vaccines.

Schistosomatoidea and Diplostomoidea

“…Whereas some human schistosomes use serine peptidases (e.g., cercarial elastase) as the main penetration enzymes, in T. szidati and T. regenti (and also in Schistosoma japonicum ) cysteine peptidases (cathepsin B-like) from the penetration glands are supposed to play a role [ 6 ]. After the attachment, the body of cercariae enters the skin, whereas the tail is removed.…”

Cysteine proteases as digestive enzymes in parasitic helminths

“…regenti and T . szidati schistosomula [ 79 , 80 ] with at least 6 isoforms of TrCB1 (1.1–1.6) identified by PCR in the former species [ 81 ]. Interestingly, when recombinantly expressed, isoforms 1.1 and 1.4 efficiently degraded myelin basic protein but not hemoglobin, consistent with T .…”

“…Like the purified zymogen of SmCB1 (above), the TrCB1.1 zymogen requires processing in trans (e.g., by SmAE) to become fully active, whereas the TcCB1.4 zymogen can autoprocess its own maturation. Like SmCB1 [ 60 ], TrCB1 is released from the parasite and may be useful as a serodiagnostic marker of infection [ 80 ].…”

Molecular evidence for distinct modes of nutrient acquisition between visceral and neurotropic schistosomes of birds

“…In the lungs, schistosomules can cause serious parasitic pneumonia, accompanied by lymphatic lesions and an influx of macrophages, heterophils and eosinophils, and/or death of the animal in severe cases 9 . Inside the host, T. szidati schistosomules evade the host’s immune response and ingest blood to acquire nutrients 10 , but the molecular basis for nutrient acquisition and their survival is unknown.…”