卵形鲳鯵对刺激隐核虫的免疫应答和免疫保护研究

用刺激隐核虫(Cryptocaryon irritans)的幼虫对卵形鲳鯵(Trachinotus ovatus)进行腹腔注射和体表感染,然后每隔一周用阻动试验(Immobilization assay)检测免疫鱼的抗血清和皮肤培养液对刺激隐核虫幼虫的阻动效价,在第14周中,分别用亚致死剂量和致死剂量的刺激隐核虫幼虫对免疫鱼攻毒以检测所产生的免疫保护力。实验结果显示:两种免疫方法都能让卵形鲳鯵的血清和皮肤生成阻动刺激隐核虫幼虫的特异性抗体,并能使被免疫鱼获得明显的免疫保护,但是体表感染免疫组的血清和皮肤培养液的阻动效价都要比腹腔注射免疫组高,所获得的免疫保护力也更强。同时还发现,免疫鱼血清和皮肤培养液中的抗体存在明显的差异:两者的最初生成时间、达到峰值的时间、变化规律以及阻动效价等都不一致。因此,我们推测鱼类的系统免疫应答和皮肤黏膜免疫应答有可能是相互独立的,或者是不同步的。鱼类的体液免疫应答,特别是黏膜免疫应答对抵御刺激隐核虫的感染起了重要的作用,采用刺激隐核虫虫体疫苗可能成为预防海水鱼类白点病的一种选择。  

IMMUNE RESPONSE AND IMMUNOPROTECTION OF POMPANOS (TRACHINOTUS OVATUS) AGAINST CRYPTOCARYON IRRITANS

The humoral immune responses and host protection of pompanos ( Trachinotus ovatus),against Cryptocaryon irritanswere determined after immunization with live theronts and killed theronts of. C. irritans. Two groups of pompanos (150 animalsper group) were immunized three times with live theronts of C. irritans by immersion at a dose of 8 103 theronts per fish or withkilled theronts of C. irritans by intraperitoneal (i. p. ) injection at a dose of 115 105 theronts per fish. The immobilization titersof antiserum and skin culture supernatant of the immunized fish were determined with an immobilization assay every two weeks.Also the immunized fish were challenged with a sublethal dose of theronts (6 103 theronts per fish) or lethal dose of theronts(2 104 theronts per fish) in Week 14. The level of C. irritans infection (indicated by relative infection level,RII) and survivalof pompanos were determined after C. irritans challenge. The results showed that the specific immobilizing antibodies could bedetected in both antiserum and skin culture supernatant in the immunized fish.Both immunization methods (immersion with livetheronts or i. p. injection with killed theronts) could confer protection to fish because when all fish were challenged with a lethaldose of theronts of C. irritans, some of the immunised fish survived,but all control fish died. There was a positive correlation be2tween higher levels of the specific immobilizing antibodies and host survival rate in the immunized fish. However,compared withi. p. injection with killed theronts,immersion with live theronts was more effective in stimulating immune responses,which indicat2ed by the higher immobilization titers in both antiserum and skin culture supernatant and the higher survival rate of the immunisedfish.When fish immunised with live theronts and killed theronts were challenged with a sublethal dose of theronts of C. irritans,the reduction rate of RII of C. irritans were 5016 % and 3712 % respectively. When fish were challenged with a lethal dose oftheronts of C. irritans,the survival rate of fish immunised with live theronts and killed theronts were 60 % and 40 % respectively.In both groups of fish,antibody levels in skin culture supernatant were much lower than those in serum. The immobilizing antibod2ies in serum and the immobilizing antibodies in skin culture supernatant of the immunized fish were different in terms of onset ofimmunity,timing,pattern of the peaks,and immobilization titers. Therefore,it is speculated that pathway of the systemic immuneresponses and mucosal immune responses were different. The present study indicates that humoral immune response,especiallymucosal immune response,plays an important role in protection against C. irritans infection.Vaccination may be an effective wayto prevent white spot disease of marine fish.