Identification of 24h Ixodes scapularis immunogenic tick saliva proteins

Abstract

Ixodes scapularis is arguably the most medically important tick species in the United States. This tick transmits 5 of the 14 human tick-borne disease (TBD) agents in the USA: Borrelia burgdorferi, Anaplasma phagocytophilum, B. miyamotoi, Babesia microti, and Powassan virus disease. Except for the Powassan virus disease, I. scapularis-vectored TBD agents require more than 24 h post attachment to be transmitted. This study describes identification of 24 h immunogenic I. scapularis tick saliva proteins, which could provide opportunities to develop strategies to stop tick feeding before transmission of the majority of pathogens. A 24 h fed female I. scapularis phage display cDNA expression library was biopanned using rabbit antibodies to 24 h fed I. scapularis female tick saliva proteins, subjected to next generation sequencing, de novo assembly, and bioinformatic analyses. A total of 182 contigs were assembled, of which ~19% (35/182) are novel and did not show identity to any known proteins in GenBank. The remaining ~81% (147/182) of contigs were provisionally identified based on matches in GenBank including ~18% (27/147) that matched protein sequences previously annotated as hypothetical and putative tick saliva proteins. Others include proteases and protease inhibitors (~3%, 5/147), transporters and/or ligand binding proteins (~6%, 9/147), immunogenic tick saliva housekeeping enzyme-like (17%, 25/147), ribosomal protein-like (~31%, 46/147), and those classified as miscellaneous (~24%, 35/147). Notable among the miscellaneous class include antimicrobial peptides (microplusin and ricinusin), myosin-like proteins that have been previously found in tick saliva, and heat shock tick saliva protein. Data in this study provides the foundation for in-depth analysis of I. scapularis feeding during the first 24 h, before the majority of TBD agents can be transmitted.

Ixodes scapularistick saliva proteins sequentially secreted every 24h during blood feeding

“…Published evidence has suggested that the tick may detoxify heme/iron through sequestration in digestive cells (hemosomes) [118,119] and hemolymph [120][121][122]. Data in this study and others [40,41,50,52,123] that show secretion of heme binding proteins in tick saliva suggest a third possibility of eliminating heme through tick saliva. Given that heme has pro-inflammatory functions [124], secretion of these proteins in tick saliva may be associated with heme sequestration, and thus allowing tick evasion of the host's inflammation defense.…”

“…Given that most housekeeping genes function inside the cell, one may argue that the high abundance of these proteins in BD and SD saliva may represent progressive SG degradation toward end of tick feeding. However, recent immuno-screening of phage display expression libraries with antibodies to 24 h I. scapularis [41] and 24-48 h A. americanum [40] tick saliva proteins that identified housekeepinglike indicates that secretion of some of the housekeeping proteins starts way before tick salivary gland degeneration, and thus, these proteins likely play important role(s) in tick feeding regulation.…”

“…However, we are encouraged by our findings that 13% (76/582) of I. scapularis tick saliva proteins in this study were reported in other tick saliva proteomes and immuno-transcriptome studies (S4 Table). Of the 76 proteins, 12 and 13 proteins were found among tick saliva immunogenic proteins that bound antibodies to 24 h I. scapularis [41] and 24-48 h A. americanum tick saliva proteins [40] respectively. Additionally one protein was identified in I. scapularis nymphs as an immunogenic protein that bound to human serum from exposure to tick bites [198].…”

“…al., [40] and Lewis et. al., [41] used antibodies to 24-48 h tick saliva proteins [42,43] to immunoscreen phage display cDNA expression libraries to identify 24-48 h Amblyomma americanum and 24 h I. scapularis immunogenic tick saliva proteins. Similar immunoscreening approaches were used to identify immunodominant I. scapularis tick saliva proteins [44][45][46][47].…”

Modulation of host immunity by tick saliva

“…A Rhipicephalus sanguineus salivary proteome showed recycling of host proteins and their secretion back into the host [32]. Lewis and colleagues used a transcriptomic approach to characterize immunogenic I. scapularis salivary proteins present after 24 hours of feeding [33]; these appeared to be involved in tick feeding even before the majority of pathogens could be transmitted.…”