卵形鲳鲹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）的幼虫对卵形鲳鲹（Trachinotus ovatus）进行腹腔注射和体表感染，然后每隔1周用阻动试验（Immobilization assay）检测免疫鱼的抗血清和皮肤培养液对激刺隐核虫幼虫的阻动效价，在第14周，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鲹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粘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，特别是粘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 irritans were determined after immunization with live theronts and killed theronts of. C. irritans. Two groups of pompanos (150 animals per group) were immunized three times with live theronts of C. irritans by immersion at a dose of 8×10³ theronts per fish or with killed theronts of C. irritans by intraperitoneal (i.p.) injection at a dose of 1.5×10⁵ theronts per fish. The immobilization titers of 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 survival of pompanos were determined after C. irritans challenge. The results showed that the specific immobilizing antibodies could be detected in both antiserum and skin culture supernatant in the immunized fish. Both immunization methods (immersion with live theronts or i.p. injection with killed theronts) could confer protection to fish because when all fish were challenged with a lethal dose of theronts of C. irritans, some of the immunised fish survived, but all control fish died. There was a positive correlation between higher levels of the specific immobilizing antibodies and host survival rate in the immunized fish. However, compared with i.p. injection with killed theronts, immersion with live theronts was more effective in stimulating immune responses, which indicated by the higher immobilization titers in both antiserum and skin culture supernatant and the higher survival rate of the immunised fish. 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 50.6% and 37.2% respectively. When fish were challenged with a lethal dose of theronts 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 antibodies in serum and the immobilizing antibodies in skin culture supernatant of the immunized fish were different in terms of onset of immunity, timing and pattern of the peaks, and immobilization titers. Therefore, it is speculated that pathway of the systemic immune responses and mucosal immune responses were different. The present study indicates that humoral immune response, especially mucosal immune response, plays an important role in protection against C. irritans infection. Vaccination may be an effective way to prevent white spot disease of marine fish.