Immunosuppressive effects of tick protein RHcyst-1 on murine bone marrow-derived dendritic cells

Ticks, as blood-feeding arthropod vectors, have evolved their own unique mechanism to suppress host immune responses and evade immune defenses in order to complete blood-feeding. The immunoregulatory effect of tick bioactive molecules on hosts has been widely reported, and the cystatin family has been identified as one of the major immunomodulators. In previous studies, we obtained a novel tick salivary bioactive protein named RHcyst-1, which belongs to the type 1 cystatin family. Here, we demonstrated the effects of RHcyst-1 on the host immune response mainly on dendritic cell (DC) function. Understanding the function of tick-derived bioactive molecule may help to clarify the mechanisms of how ticks escape the host immune response and help to control ticks and tick-borne disease transmission.

Bone marrow-derived DCs (BMDCs) were generated and induced by GM-CSF and IL-4 with or without RHcyst-1 addition. Flow cytometry was used to analyze the differentiation and maturation of BMDCs and T cell cytokine production. Quantitative real-time PCR (qRT-PCR) and western blot were used to measure changes in expression within STAT and p38 MAPK signaling pathways.

Flow cytometry analysis revealed that RHcyst-1 inhibited the differentiation of BMDCs, but had no effect on the maturation of BMDCs. T cells co-cultured with DCs treated with RHcyst-1 produced significantly less TNF-α, IFN-γ and IL-2 than the control group. Further analysis showed that the mRNA level and phosphorylation of p38, ERK and STAT were significantly changed after RHcyst-1 added to bone marrow monocytes during the differentiation stage.

Our results suggest that RHcyst-1 is one of the major immunosuppressive proteins of BMDC function from blood-feeding ticks.