Preliminary Study On The Impact Of Host Immune Cells By Adult Trichinella Spiralis Seirne Protease

Trichinosis is a zoonosis caused by eating raw or undercooked meat containingL1infective larvae of Trichinella. Although fatality rate of this disease is low, andsevere infection can cause serious heart and brain damage which lead to death, adultworms can inhibit host immune system which interferes the immunization effect ofbacteria, viruses and other parasites and greatly increases the possibility of otherpathogens to invade host posing a significant threat to human health during theintestinal phase. The uncertainty of immunomodulatory molecules by Trichinella andits unknown mechanism make no progress on research and development of preventiveagents about Trichinella. The cDNA library of adult worm was constructed, and aserine protease gene named Zh68was acquired by immunological screening whichhas high abundance and strong antigenicity. Serine protease secreted by parasitesinvolves the interaction between host and parasite, such as the invasion of host tissues,absorption of nutrients and escape of host immune response. Serine proteases havebeen recommended to be a diagnostic marker of infectious diseases and the candidatesof vaccine.Trichinella spiralis primarily modulate host immune response through immunecells. So we monitor the dynamics of host immune cells during the intestinal phase toanalyze variation of host immune suppression. Kunming mouse were infected with500L1larvae orally. The adult worms recovery rate was65%at1day post infection(dpi), and the adult worm were eliminated from mouse intestine until17dpi; Thenumber of adult worms was stable from5dpi to9dpi, and during this period femalesrelease a large number of newborn larvae with a peak at7dpi. Flow cytometry showus that CD4~+T lymphocytes decrease significantly and the proliferative response of Tlymphocytes to ConA reduced at7dpi. Interestingly, we also acquired a specificserine protease from newborn larvae cDNA library constructed by us previously.Thereby the phenomenon at7dpi may result from a joint role of Zh68and newbornlarvae’s specific serine protease. T lymphocytes increased with CD8~+T lymphocytes dominant before7dpi, thus the ratio of CD4~+/CD8~+decreased indicated the immunityof mouse decreased. After11dpi, CD4~+T lymphocytes began to increase whichsuggested mouse immune system restored gradually. What surprised us is substantialdecline in macrophages and the loss of proliferative response of B lymphocytes toT.spiralis antigens, despite the sensitivity of B lymphocytes to LPS stimulationincreased. The number of macrophages began to recovery followed by the rise of Blymphocytes.Considering that murine macrophages change dramatically during the intestinalphase, the mechanism of serine protease in adult worm ES on macrophages wasfurther studied. CCK-8revealed toxicity of adult worm’s ES on S774A.1macrophages in dose-dependent and time-dependent manner, but this effect wassignificantly decreased when ES were treated by Zh68antibody. Flow cytometryshowed that adult worm serine protease could induce S774A.1macrophagesapoptosis.The studies of gene associated with immune evasion mechanism of T.spiralis arescare. So the further study about adult T.spiralis serine protease’s function and its rolein parasite invasion will clarify the invasion mechanism of T.spiralis and provide asolid basis for the exploitation of new anti-T.spiralis drugs and biologic agents.