Date Published: April 8, 2018
Author(s): Martin Omulindi Oyugi, Johnson Kangethe Kinyua, Esther Nkirote Magiri, Milcah Wagio Kigoni, Evenilton Pessoa Costa, Naftaly Wang’ombe Githaka.
Ticks cause approximately $17–19 billion economic losses to the livestock industry globally. Development of recombinant antitick vaccine is greatly hindered by insufficient knowledge and understanding of proteins expressed by ticks. Ticks secrete immunosuppressant proteins that modulate the host’s immune system during blood feeding; these molecules could be a target for antivector vaccine development. Recombinant p36, a 36 kDa immunosuppressor from the saliva of female Dermacentor andersoni, suppresses T-lymphocytes proliferation in vitro. To identify potential unique structural and dynamic properties responsible for the immunosuppressive function of p36 proteins, this study utilized bioinformatic tool to characterize and model structure of D. andersoni p36 protein. Evaluation of p36 protein family as suitable vaccine antigens predicted a p36 homolog in Rhipicephalus appendiculatus, the tick vector of East Coast fever, with an antigenicity score of 0.7701 that compares well with that of Bm86 (0.7681), the protein antigen that constitute commercial tick vaccine Tickgard™. Ab initio modeling of the D. andersoni p36 protein yielded a 3D structure that predicted conserved antigenic region, which has potential of binding immunomodulating ligands including glycerol and lactose, found located within exposed loop, suggesting a likely role in immunosuppressive function of tick p36 proteins. Laboratory confirmation of these preliminary results is necessary in future studies.
Ticks are considered among the most important vectors of livestock diseases worldwide as well as major vectors of pet diseases . In tropical Africa, ticks and the tick-transmissible diseases constitute a major obstacle to livestock development . Like elsewhere in the world, chemical acaricides have been the mainstay of tick control in this region; however, increasing resistance to this group of insecticides threatens livestock production systems, especially small-holding sectors that rely on rearing of exotic cattle breeds that are more susceptible to tick infestation and tick-borne diseases [TBDs] . Integrated tick control incorporating reduced acaricide use, breeding cattle for tick resistance, rotational grazing, and use of vaccines presents a sustainable and long-term strategy to the control of ticks and TBDs in the tropics .
The p36 immunosuppressive proteins from ticks exhibit antigen traits worth evaluating in future experimental in vitro and in vivo trials. This includes potential conservation across several tick species and presence of a likely conserved antigenic region that may be bound by immunomodulator ligands such as glycerol and lactose. A further study is necessary on suitability of this potentially conserved region in development of a multi/chimeric antitick vaccine that incorporates critical antigenic regions. The predicted 3D model of D. andersoni p36 protein may be used as a template to model structures of other orphan proteins related to p36. This work is a step towards developing cross-protective next-generation antitick vaccines, as the results expand our knowledge of p36 tick saliva protein and lay ground for future studies to determine their exact role in tick feeding process, which is useful in designing blockade approaches targeting these proteins.