ITGA2B and bacterial infectious disease: In the past two decades, several subpopulations of T cells (i.e., CD8+, CD4-1+, CD4-2+, and TCRγδ+ T cells) have been identified in various fish species such as carp, rainbow trout, pufferfish, and zebrafish; their immunological functions regarding cytotoxicity, resistance to bacterial infection and allogeneic cell transfer, or antigen presentation have also been preliminarily confirmed [14–23].