Immunoglobulin G binding protein (IGBP) from Rhipicephalus haemaphysaloides: identification, expression, and binding specificity

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 ttest) 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.