Comparative studies on the immunogenicity of theronts, tomonts and trophonts of Cryptocaryon irritans in grouper

Abstract

Cryptocaryon irritans is a ciliated obligate parasite of marine fish, causing white spot disease in tropical and sub-tropical regions. Recent studies have shown that fish can mount immune responses against C. irritans and acquire protection. The present study compared the protective immunity in grouper (Epinephelus coioides) against C. irritans induced by theronts, trophonts and tomonts via intraperitoneal (i.p.) injection and tentatively identified an immobilization antigen. Specific antibody titres of immunized fish serum were determined by enzyme-linked immunosorbent assay and immobilization assays at weeks 0, 1, 2, 4, 6 and 8 post-immunization, and immunized grouper were challenged with theronts to detect the survival percentage of fish. Fish immunized with theronts produced higher levels of serum antibody against C. irritans than fish immunized with trophonts or tomonts. A significantly higher level of immune protection was achieved in fish immunized with theronts but not in fish immunized with tomonts or trophonts. Western blot analysis using polyclonal immobilization antibodies of rabbit immunized with theront revealed an immunoreactive band of the protective (immobilization) antigens of C. irritans, the size of which is approximately 34 kDa. The sera of mice immunized with the protein could immobilize theronts of C. irritans. These results demonstrated that the theront stage of C. irritans elicited stronger protective immunity than the trophont and tomont stages in grouper. The tentative identification of protective antigen provides the solid foundation for the development of a defined vaccine against C. irritans.

Elicited cross-protection and specific antibodies in Mozambique tilapia (Oreochromis mossambicus) against two different immobilization serotypes of Cryptocaryon irritans isolated in Hawaii

“…Most studies on the protection mechanism against C. irritans have been focused on the antibody responses [20,31]. However, the potential involvement of innate immune responses during the early stages of infection following the invasion of the theronts should also be considered because innate immunity is the first line of defense against many pathogens [32].…”

Orange-spotted grouper (Epinephelus coioides) TLR2, MyD88 and IL-1β involved in anti-Cryptocaryon irritans response

“…C. irritans, just like Ichthyophthirius multifiliis, is one of the best models to study the antiparasitic immune response in fish. Recently, our lab has reported that fish can mount a humoral immune response to C. irritans and has also shown that a specific antibody could immobilize C. irritans theronts in vitro [33,34]. However, the role of an innate immunity response to C. irritans in fish is more poorly understood.…”

Immune protection of Mozambique tilapia (Oreochromis mossambicus) exposed to different infectious doses of ectoparasite (Cryptocaryon irritans)

“…Previous studies used tomonts (Yambot and Song 2006) or theronts (Luo et al 2007;Bai et al 2008) for challenge exposures. However, in the case of using tomonts, since each tomont has variable excystment time, occurring between 3 and 72 days (Colorni and Burgess 1997), experimental fish must be maintained under continual exposure to C. irritans until all tomonts excyst.…”