While CD4-1+ cells have been revealed to play a pivotal role against viral diseases in ginbuna crucian carp (Carassius auratus) (62), a study using olive flounder as the animal model showed that CD4-2 helper T-cells proliferated earlier and higher in number than CD4-1 cells (66), suggesting that CD4-2 cells are important in the early phase of cell-mediated immunity. Here, ITGA2B is linked to viral load.