1. Recombinant Ixodes scapularis Calreticulin Binds Complement Proteins but Does Not Protect Borrelia burgdorferi from Complement Killing.
- Author
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Ansari MA, Nguyen TT, Kocurek KI, Kim WTH, Kim TK, and Mulenga A
- Abstract
Ixodes scapularis is a blood-feeding obligate ectoparasite responsible for transmitting the Lyme disease (LD) agent, Borrelia burgdorferi . During the feeding process, I. scapularis injects B. burgdorferi into the host along with its saliva, facilitating the transmission and colonization of the LD agent. Tick calreticulin (CRT) is one of the earliest tick saliva proteins identified and is currently utilized as a biomarker for tick bites. Our recent findings revealed elevated levels of CRT in the saliva proteome of B. burgdorferi -infected I. scapularis nymphs compared to uninfected ticks. Differential precipitation of proteins (DiffPOP) and LC-MS/MS analyses were used to identify the interactions between Ixs ( I. scapularis ) CRT and human plasma proteins and further explore its potential role in shielding B. burgdorferi from complement killing. We observed that although yeast-expressed recombinant (r) Ixs CRT binds to the C1 complex (C1q, C1r, and C1s), the activator of complement via the classical cascade, it did not inhibit the deposition of the membrane attack complex (MAC) via the classical pathway. Intriguingly, r Ixs CRT binds intermediate complement proteins (C3, C5, and C9) and reduces MAC deposition through the lectin pathway. Despite the inhibition of MAC deposition in the lectin pathway, r Ixs CRT did not protect a serum-sensitive B. burgdorferi strain (B314/pBBE22 Luc ) from complement-induced killing. As B. burgdorferi establishes a local dermal infection before disseminating to secondary organs, it is noteworthy that r Ixs CRT promotes the replication of B. burgdorferi in culture. We hypothesize that r Ixs CRT may contribute to the transmission and/or host colonization of B. burgdorferi by acting as a decoy activator of complement and by fostering B. burgdorferi replication at the transmission site.
- Published
- 2024
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