Fish CD8+ T cells: Current knowledge and research perspectives

Cell-mediated cytotoxicity is a defense mechanism in which host immune cells kill infected cells. Cell-mediated cytotoxicity refers to the Major Histocompatibility Complex Class (MHC) restricted killing of infected cells with CD8 + T cells serving as key players. Intracellularly processed antigenic peptides are displayed by MHC-I molecules at the cell's surface for surveillance of immune cells. Naïve CD8 + T cells patrolling the lymphoid and peripheral tissues recognize the MHC-I loaded cognate peptide (pMHC-I) via their specialized T cell receptor (TCR). This results in TCR/pMHC-I binding and initiation of a cascade of events to facilitate T cell activation and subsequent differentiation into effector/cytotoxic CD8 + T cells (CTLs). Effector CTLs typically produce effector molecules and cytokines including granzymes, perforins and IFN-γ to eliminate infected cells. Fish cell-mediated cytotoxic response is complex and is far from understood. This review provides a general overview of the current knowledge of CD8 + cell mediated cytotoxic responses in fish and highlights the research gaps that need to be filled.