Preliminary study on the annual variation of five immune factors in female parent and offspring of Ctenopharyngodon idella with maternal immunization by grass carp reovirus (GCRV) attenuated vaccine

Ctenopharyngodon idella is the most productive cultured freshwater fish species in China, while the healthy development of grass carp industry has been restricted for a long time by grass carp hemorrhage disease caused by grass carp reovirus (GCRV) infection. The selective breeding of C. idella with high resistance is a research focus of industry and academia. Our previous research found that maternal immunization could significantly enhance the offspring resistance to GCRV. To investigate the expression characteristics of maternal immune factors in the female parent treated with GCRV attenuated vaccine and its offspring, the protein concentration and gene expression levels of five different immune factors (IgM, C3, LZM, MBL and Bf) were detected by ELISA and qPCR in the blood of female parent, the early development embryos and juvenile fish of offspring. The results showed that the protein concentration and gene expression level of five immune factors in female parent blood by GCRV attenuated vaccine (experimental group) were 1.5 times higher than those in the control group, but there was no significant difference between the two groups after 11 months of immunization. The gene expression level of IgM, C3, MBL and Bf in experimental group offspring were higher than those of the control group on day 4. The protein concentration level of IgM, C3 and Bf in experimental group offspring were slightly higher than those of the control group on day 15. Five immune factors were still highly expressed in experimental group offspring immune organs such as liver, spleen, kidney and head kidney at the age of 5-11 months. The results indicated that the expression levels of immune factors in the female parent treated with GCRV attenuated vaccine and its offspring significantly increased after maternal immunization by GCRV attenuated vaccine, but it has a certain time-effectiveness. The high expression of immune factors in the female parents and offspring might last up to 11 months, which provides a reference for the maternal immune procedure in C. idella and molecular information for the breeding of C. idella with viral resistance.