As the second most important human ectoparasite, ranked only after mosquitoes, the tick threatens the development of husbandry and even the health of humans worldwide. Immunoglobulin G binding proteins (IGBPs) are considered to be the major factors used by ticks to evade the host immune system and the damage caused by host antibodies. In this study, an IGBP-MB homologue was identified in the tick , which was predominantly detected in the salivary glands and hemolymph of male ticks. Recombinant IGBP (rIGBP/His) displayed significant binding activity to IgGs from rabbits and pigs, and bound to the F(ab)’2 but not the Fc fragment of rabbit IgG. Although the silencing of IGBP expression in ticks had no obvious effect on their blood-feeding and subsequent oviposition, antibodies raised to rIGBP/GST reduced the replete body weight (218.9 ± 20 mg in the control group vs. 142.5 ± 43.3 mg in the test group,  < 0.05 by Student’s  test) and increased the mortality of the ticks. This study extends our understanding of the immunoevasive function of IGBPs and is a step towards the development of a vaccine against ticks.

As the second most important human ectoparasite, ranked only after mosquitoes, the tick threatens the development of husbandry and even the health of humans worldwide. Immunoglobulin G binding proteins (IGBPs) are considered to be the major factors used by ticks to evade the host immune system and the damage caused by host antibodies. In this study, an IGBP-MB homologue was identified in the tick Rhipicephalus haemaphysaloides, which was predominantly detected in the salivary glands and hemolymph of male ticks. Recombinant IGBP (rIGBP/His) displayed significant binding activity to IgGs from rabbits and pigs, and bound to the F(ab)’2 but not the Fc fragment of rabbit IgG. Although the silencing of IGBP expression in ticks had no obvious effect on their blood-feeding and subsequent oviposition, antibodies raised to rIGBP/GST reduced the replete body weight (218.9 ± 20 mg in the control group vs. 142.5 ± 43.3 mg in the test group, P < 0.05 by Student’s t test) and increased the mortality of the ticks. This study extends our understanding of the immunoevasive function of IGBPs and is a step towards the development of a vaccine against ticks.

To subclone and express the gene encoding the immunoglobulin binding protein(IGBP) of Rhipicephalus haemaphysaloides tick and analyze its immune protective effect,the IGBP gene was cloned into vector pGEX-4T-1,then transformed to Escherichia coli BL21 cells and expressed by the induction with IPTG.The expressed product was purified and used as antigen to immunize rabbits in order to evaluate its immune protective effect.The rabbits in the vaccinated group were immunized with 500 μg of the recombinant protein emulsified with 206-adjuvant,while those in the control group injected with PBS emulsified with 206 adjuvant.The immunization consisted of the triple injections at weeks 0,2 and 4,respectively.All the rabbits were challenged with R.haenaphysaioides ticks 2 weeks after the final injection in order to evaluate the immune effect.It was found that the fusion protein GST-IGBP was highly expressed in E.coli in the form of the inclusion bodies.There were significant differences in tick weights and mortalities between the vaccinated and control groups.It is evident that the IGBP gene can be highly expressed in E.coli and the fusion proteins GST-IGBP can produce the anti-tick protective immunity to a certain degree.

The study was based on the EST data of Suppressed Subtractive Hybridizaiton cDNA library of fed and unfed male Rhipicephalus haemaphysaloides.Firstly,we obtained the full-length sequence of IgG binding protein(IGBP)from rapid amplification of cDNA ends protocol.The gene had 683 bp encoding 178 amino acid residues with 19.5 kDa predicted molecular weight and showed a rather high homology(92% cDNA identities)with Rhipicephalus appendiculatus IGBP-MB.Secondly,the expression feature of male specific,in the different organs and phages,were analysised by the reverse transcription polymerase chain reaction method(RT-PCR),the results suggested the expression of IGBP gene had no male specific characteristic,and IGBP gene was expressed in the salivary,shell,eggs,unfed larva,unfed nymphae and adult,but not expressed in the gut.

The immunoglobulin binding proteins(IGBPs)mainly distribute in the hyaemolymph and salivary gland of ticks.IGBPs can bind host immunoglobulin(Ig)in the haemolymph of ticks and prevent tick organs from damaging by host immunoglobin.The elucidation of the structure and function of the IGBPs will provide clues to the research of vaccine against ticks.This paper reviewed the research progress of the IGBPs.