The immune battlefield: The impact of inflammatory cytokines on CD8+ T-cell immunity

Soldiers of the immune system: CD8 + T-cell basicsWithin the microscopic world, there is an ongoing war between the host and foreign invaders, and the battlefield is the immune system.When a pathogen encounters innate immune cells, such as dendritic cells (DCs), it is quickly recognized as foreign.The DCs provide alarm signals in the form of inflammatory cytokines, degrade the pathogen, and present pathogen-derived peptides to adaptive immune cells, including CD8 + T cells.The primary function of CD8 + (or cytotoxic) T cells is to recognize and kill infected cells.They are critical soldiers of the immune system, but before carrying out their function, they must receive 3 signals to become appropriately activated.A naïve CD8 + T cell must have T-cell receptor (TCR) engagement by peptide: major histocompatibility complex (MHC) complexes from the antigen-presenting cell (signal 1) [1-5], ligation of costimulatory receptors (signal 2) [4,[6][7][8][9][10][11], and receive specific cytokine signals (signal 3), which are required for optimal cell accumulation, proliferation, and function [9,[12][13][14][15].After integrating the proper signals, the newly activated antigen-specific CD8 + T cells undergo clonal expansion [16-18] and develop into "effectors" that have acquired the capacity to kill pathogen-infected host cells [1,12,[19][20][21][22].Following clonal expansion, 90%-95% of the pathogen-specific effector CD8 + T-cell population numerically contracts via apoptosis [18,23,24], and the remaining 5%-10% of cells constitute a long-lived memory CD8 + T-cell pool that provides enhanced protection from secondary infection (Fig 1A) [18,23,25,26].The development of the long-lived memory CD8 + T-cell pool is not a stochastic event, and the cells that seed this population can be identified among effector T cells early following infection.Thus, effector CD8 + T cells can be broadly divided into the following 2 subsets: memory precursor effector cells (MPECs), which will predominantly become long-lived memory CD8 + T cells and short-lived effector cells (SLECs), which are mostly lost during contraction after the T-cell response [27].The establishment of a pool of memory CD8 + T cells is the goal of T-cell vaccination strategies, and understanding how to modulate their function is critical for vaccine development and immunotherapies. CD8 + T-cell battalion: How the host benefits from pathogeninduced inflammationFollowing infection, inflammatory cytokines (i.e., signal 3) are induced to counter the invading pathogen and to alarm the immune system.Pathogen-induced inflammatory cytokines impact several aspects of memory CD8 + T-cell biology.In addition to serving as signal 3 during the activation of naïve T cells, inflammatory cytokines regulate the antigen sensitivity, proliferation, and trafficking of both effector and established memory T-cell populations, giving the

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