Study On The Immunogencity Of Liposome-encapsulated Vaccine And PLGA Microspheres-encapsulated Vaccine Against Stenotrophomonas Maltophilia Infection In Channel Catfish (Ictalurus Punctatus)

The effect of the liposome-encapsulated antigen of Stenotrophomonas maltophilia and PLGA microspheres-encapsulated antigen of Stenotrophomonas maltophilia on immune function and potential protective efficacy against S.maltophilia infection in Channel Catfish(Ictalurus punctatus) were studied respectively.The results wvere as follows:1.PLGA microspheres-encapsulated vaccine was prepared by using a water-in oil-in water(w/o/w) emulsification/solvent evaporation method.Channel Catfish was divided into fifteen groups.Each method which was employed for administration of antigen:immersion, injection and oral vaccination had five groups,different dosage of PLGA microspheres-encapsulated vaccine(groupâ… -groupâ…¢),saline(groupâ…£) and S.maltophilia antigen alone(groupâ…¤),3 times at 2-week intervals.On weeks 0-7, phagocytic activity of leucocytes and bactericidal activity of phagocytes were tested by using MTT dying method;lysozyme,C₃,protein and IgM in serum were detected by using kit.On week 9,all fish were challenged by injection with 1×10⁹cfu/ml S.maltophilia to investigate the protective efficacy.The vaccines of PLGA microspheres-encapsulated bacterial antigen were obtained successfully.The mean diameter was 2.2±0.5μm.After immunization,phagocytic activity,bactericidal activity,lysozyme,C₃,protein and IgM were detected significantly.Channel Catfish immunized by injection were challenged with S.maltophilia alive,the relative survival rates of group 3(73.33%) was 9.16%higher than group 5(64.17%),group 2(66.68%) was 2.51%;however group 1(49.17%) was 15% lower than group 5.Another five groups which immunized by oral vaccination were challenged with S.maltophilia alive,the relative survival rates of group 1 to group 3 were 43.33%,65%,75%,but group 5 was a mere 6.68%,and the results suggest that PLGA microspheres-encapsulated antigen of S.maltophilia have the potential for induction of protective immune response against S.maltophilia infection.However the protective efficacy of Channel Catfish immunized by immersion was not good,due to it's mass.2.Liposome-encapsulated vaccine was prepared by using reverse-phase evaporation method and the size of liposome was measured by electron microscopy.Channel Catfish was divided into fifteen groups.Each immune method had five groups,different dosage of liposome-encapsulated vaccine(group 1-group 3),saline(group 4) and S.maltophilia antigen alone(group 5),3 times at 2-week intervals.On weeks 0-7,phagocytic activity of leucocytes and bactericidal activity of phagocytes were tested by using MTT dying method;lysozyme,C₃,protein and IgM were detected by using kit.On week 9,all fish were challenged by injection with S.maltophilia alive to investigate the protective efficacy.The vaccines of liposome-encapsulated bacterial antigen were obtained successfully.The size of liposome was round,and its mean diameter was 0.9±0.3μm.After immunization, phagocytic activity,bactericidal activity,lysozyme,C₃,protein and IgM were detected significantly.Charmel Catfish immunized by injection were challenged with S.maltophilia alive,the relative survival rates of group 2(70.83%) was 6.66%higher than group 5 (64.17%),group 3(80%) was 15.83%,however group 1(53.33%) was 10.84%lower than group 5.Another five groups which immunized by oral vaccination were challenged with S.maltophilia alive,the relative survival rates of group 1 to group 3 were 39.18%,51.68%, 58.33%,but group 5 was a mere 6.68%,and the results suggest that liposome-encapsulated vaccine could protect immunogeneity of antigen obviously.However the protective efficacy of Channel Catfish immunized by immersion was not good,because of positive ion and organics in water.