In our study, we found that the mRNA expression of TNFRSF10B and CASP3 was significantly increased in the infected flounders at 72 hpi, and the apoptotic rates of mIgM+ B lymphocytes were also found to be significantly increased, suggesting the possibility of mIgM+ B lymphocytes relying on apoptosis to combat viral infections at low temperature. Here, CASP3 is linked to viral infectious disease.