Abstract
Repeated exposure of rabbits and other animals to ticks results in acquired resistance or immunity to subsequent tick bites and is partially elicited by antibodies directed against tick antigens. In this study we demonstrate the utility of a yeast surface display approach to identify tick salivary antigens that react with tick-immune serum. We constructed an Ixodes scapularis nymphal salivary gland yeast surface display library and screened the library with nymph-immune rabbit sera and identified five salivary antigens. Four of these proteins, designated P8, P19, P23 and P32, had a predicted signal sequence. We generated recombinant (r) P8, P19 and P23 in a Drosophila expression system for functional and immunization studies. rP8 showed anti-complement activity and rP23 demonstrated anti-coagulant activity. Ixodes scapularis feeding was significantly impaired when nymphs were fed on rabbits immunized with a cocktail of rP8, rP19 and rP23, a hall mark of tick-immunity. These studies also suggest that these antigens may serve as potential vaccine candidates to thwart tick feeding.
Highlights
Ixodes scapularis and Ixodes ricinus ticks transmit pathogens such as Borrelia, Babesia, Anaplasma and selected flaviviruses [1]
A Yeast Surface Display (YSD) expression library of I. scapularis salivary gland cDNAs was probed with purified IgG from pooled sera from nymphimmune rabbits
Several studies have shown a critical role for the humoral response in tick immunity [16,36] and provided the impetus to identify antigens that elicit tick-immunity by exploiting approaches including immunoscreening of cDNA expression libraries generated in routine prokaryotic expression systems [22,23]
Summary
Ixodes scapularis and Ixodes ricinus ticks transmit pathogens such as Borrelia, Babesia, Anaplasma and selected flaviviruses [1]. Tick saliva contains proteins that inhibit T-cells [3], Bcells [4], the complement system [5,6,7,8], dendritic cells [9] and the coagulation system [10,11,12,13]. Even though ticks modulate and dampen host immune responses to ensure successful feeding, upon repeated tick infestations some animals develop an immune response resulting in tick rejection. This phenomenon, referred to as ‘tick immunity’, was first described by William Trager in 1939, when he observed that Dermacentor variabilis ticks were not able to efficiently engorge on guinea pigs that had previously been exposed to several tick infestations [14]. Basophils, eosinophils [15], and antibodies [16] against exposed and concealed [17] tick proteins play a role in tick-immunity
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