Detection Of Inflammation Triggered By Very Virulent Infectious Bursal Disease Virus And Study On The Inflammation Promoted By HMGB1

Infectious bursal disease(IBD)is an acute,fatal,and highly contagious disease that is caused by infectious bursal disease virus(IBDV).IBDV has evolved classic IBDV(cIBDV),variant IBDV(vIBDV),and very virulent IBDV(vvIBDV)strains.The high lethality of vvIBDV has brought huge scale economic loss to the world poultry industry.The vvIBDV infection can cause typical inflammatory symptoms,such as bleeding,injury,and atrophy of bursa.It also can lead to different degrees of inflammation of muscle,glands,and stomach,but the process and molecular basis of triggering inflammation and mortality in detail is still unclear.The inflammatory response triggered by vvIBDV has been detected through the clinical,pathological,and molecular levels.Serious clinical symptoms,rapid onset,and peaked mortality could be found in vvIBDV Gx infected SPF chicks.The lesions during this period were manifested as multi-organ inflammation,especially in the bursa of Fabricius.Histopathological examination revealed that the structural integrity of the bursal follicles of infected chickens was impaired,there was a large infiltration of inflammatory cells,B cells disintegrated into cell debris and phagocytized by macrophages.At the molecular level,the up-regulated expression of inflammatory cytokines IL-1? and IL-18 could be detected by qRT-PCR.The increased levels of IL-1? and IL-18 in serum could be detected by ELISA.The above results indicate that the inflammation is an important process of vvIBDV disease.The damage associated molecule pattern(DAMP)is closely related to inflammation.In this study,expression of six DAMP molecules were detected by q RT-PCR in the inflammation induced by vvIBDV infection.The study found that most of the DAMP molecules were up-regulated in the spleen and down-regulated in the bursa of Fabricius.This was positively correlated with the changes of the expression of IL-1? and IL-18.This suggests that DAMP may be closely related to IBDV inflammation.Furthermore,we focused on the detection of high mobility group box 1(HMGB1),an important member of DAMP,during vvIBDV inflammatory process.The up-regulated levels of HMGB1 were deteced in serum and inflammatory exudate of bursa.Different virulence of IBDV infection also confirmed the above data.Based on these,we speculate that HMGB1 can play an important role in the inflammatory process induced by vv IBDV.To confirm this hypothesis,a model of vvIBDV infection in vitro has been established in B lymphocytes(DT40 cells).On this basis,the study found that vvIBDV Gx strain infection reduced intracellular HMGB1,and more HMGB1 were released outside from DT40 cell.Intracellular HMGB1 exerted anti-IBDV replication.This was demonstrated by the effects of up-regulated expression,knockdown,and suppression of HMGB1 on IBDV replication.The extracellular HMGB1 released as an inflammatory mediator plays a proinflammatory role.Consequently,purified HMGB1 was used to stimulate chicken macrophage cell line HD11 in vitro,as a result,IL-1? and IL-18 in the supernatant of HD11 were increased.At the same time,HMGB1 significantly increased casepase-1 kinase activity inNLRP3 inflammasome of HD11 cell.This suggests a possible mechanism of inflammation induced by vv IBDV.The vv IBDV infection triggers B cell to release HMGB1 so that the levels of HMGB1 in local tissue and blood were increased.HMGB1 is involved in the activation of NLRP3 inflammasomes of macrophage.The caspase-1 kinase activity promotes the maturation of IL-1? and IL-18,which promotes the inflammatory response.In this study,multi-angle detection proved that vvIBDV infection induced inflammation,revealed the important role of HMGB1 in anti-virus,pro-inflammatory in vvIBDV infection,and the relevant molecular mechanism was further explored.This study is of great significance for in-depth understanding of the pathogenic process of IBDV and for exploring more effective disease prevention and control strategies.