The Immune Response Of Host To The Infection Of Haemaphysalis Longicornis

Haemaphysalis longicornis is widely distributed and there is a diversity of its host species.It is specific to blood sucking and is parasitized in vitro,which may lead to multiple diseases through carrying a variety of pathogens.Therefore,the study of H.longicornis has an important economic and epidemiological significance.There is a complex immune relationship between ticks,host and pathogens.The interactions include the immune response of the tick to the host and the immune response of the host to the tick infection.After being infected by a tick,the host may produce a series of immune responses that affect the blood sucking,growth and fertility of ticks.In the present study,we mainly investigated the immunological response produced by rabbit to H.longicornis infection.We used the ELISA method to detect the dynamic changes of the content of TNF-α,ICAM-1 and IL-1β in the blood of rabbits after primary and re-bite of H.longicornis.The rabbits were divided into the primary bite group and the rebite group,respectively.And 15 pairs of H.longicornis were put on the ears of each rabbit.In the primary bite group,the blood samples were collected from the marginal vein for ELISA detection before bite,and 24 h,48h,72 h,5d and 8d after bite.Rabbits in the re-bite group were re-infected with H.longicornis at two weeks after primary bite,and ELISA was performed at the same time points.Results showed that the concentrations of TNF-α,ICAM-1 and IL-1β increased significantly at 24h~48h after primary bite.Moreover,the concentrations of the three inflammatory cytokines reached peak at 48 h,which were significantly higher than that of pre-bite(P < 0.05).After 72 h,the concentrations decreased slowly.When the rabbit was re-bite with H.longicornis,the concentration of three inflammatory factors increased rapidly,and was also reached peak at 72 h.In the re-bite group,the concentration of TNF-α was 962.35 pg/ml at 72 h after infection,which was two times higher than that of the same time point in the primary bite group(P < 0.05).The concentration of ICAM-1 was no significant difference between the re-bite group and primary bite group at 48 h after infection,and then reached peak at 72 h.The concentration of ICAM-1 was 4032.47 pg/ml at 72 h after infection.In the re-bite group,the concentration of IL-1β was significantly higher than those in the primary bite group(P<0.05).5d~8d after reinfection,the concentrations of the three inflammatory cytokines decreased slowly.The above results indicated that the degree of inflammatory reaction in the re-bite group was significantly higher than that of the primary bite group,the concentrations of TNF-α,ICAM-1 and IL-1β increased more rapidly,and the duration of high concentrations was longer.This indicated that innate immunity produced inflammatory cytokines to participate in the immune response after primary infection of H.longicornis.The resistance of rabbits was low at that moment,therefore,the production of inflammatory cytokines was slow,the concentrations were low and the duration of high concentration was short.When the rabbits were re-bite,with some produced resistance,acquired immunity played an important role.This resulted in a rapidly increase of the concentration of inflammatory cytokines and a longer duration time of high concentration.The important immune function of inflammatory cytokines eventually blocked the bite and blood sucking of H.longicornis.qRT-PCR was performed to detect the expression of TLR-2,TLR-4 and TLR-6 in lymphocytes at 72 h after infection in the primary bite group and the re-bite group,respectively.Results indicated that the expression level of TLR increased with the increase of the number of infection.The expression level of TLR-2,TLR-4 and TLR-6 in the primary bite group were increased than that of pre-bite group(P<0.05).The expression level of TLR in the re-bite group were significant higher than that of the primary infection group.This indicated that after infection by H.longicornis,TLR was involved in innate immune response,and induced a series of gene activation through signal transduction pathway,which resulted in the secretion of inflammatory cytokines and chemokines,eventually triggering systemic inflammatory response.Additionally,TLR played an important regulatory role in the acquired immune response after reinfection.The above results of comprehensive experiments demonstrated that inflammatory cytokines TNF-α,ICAM-1,IL-1β and TLR were involved in the innate immune response and the acquired immune response produced by infection of H.longicornis in rabbits.After primary infection,the resistance of rabbits was low,the concentration of inflammatory cytokines was slowly increased and the duration of high concentration was short,and the expression of TLR was low.When the rabbits were re-infected,with some produced resistance,acquired immunity played an important role,which resulted in a more obvious and rapidly increase of the inflammatory cytokines and the high expression of TLR.