The most considerable changes occurred early after infection (day 1.5) and waned during late infection (day
7) . At the early time point (day 1.5), NK cells were activated, and genes encoding inflammatory (Cd69, Ifih1, Ifitm3), proliferation (Il2ra), and effector (Ifng, GzmB) function were upregulated . Meanwhile, genes encoding the suppressors of cytokine signaling Socs1 and Socs3 were also highly expressed at this early time point to avoid uncontrolled inflammation. At the late stage of the infection (day 7), Ly49H+ NK cells achieved the peak of clonal expansion with higher expression of genes encoding cell cycle or proliferation-related genes (including cell-division cycle genes and MKI67). A contraction phase then occurs in which most effector Ly49H+ NK cells undergo cell death and leave see more behind long-lived memory NK cells (day 27) that persist for months . These memory NK cells are able PCI-32765 chemical structure to mount a robust secondary response against previously encountered pathogens and have higher IFN-γ transcripts than naïve NK cells . At day 27 after infection, genes including Ly6c1, Fasl, and Casp1 were more highly expressed in memory than in naïve NK cells . Thus, profiling the transcriptional dynamics within NK cells during MCMV infection has shed light on the potential cellular
processes that may be involved in the differentiation of naïve NK cells into effector and memory cells. Resting NK cells have minimal cytotoxic function; upon activation, NK cells gain the ability to kill target cells using the granule exocytosis pathway immediately upon recognition of transformed or infected cells through the interactions between receptors and ligands. At the molecular level, resting human CD56bright and CD56dim NK cell subpopulations as well as mouse NK cells are in a persistently “alerted” state containing abundant granzyme A, granzyme B, and perforin at the mRNA level, but contain only granzyme A at the protein level [29, 41, 43, 72]. Upon cytokine activation in vitro, NK cells drastically increase their
granzyme B and perforin protein levels without major changes in the abundance of their respective 4-Aminobutyrate aminotransferase mRNA [41, 72]. The same pattern of regulation occurred in NK cells in vivo after MCMV infection . These data suggest that resting NK cells have minimal cytotoxic function due to a block in perforin and granzyme B mRNA translation and that NK-cell activation functions to release this block, although the specific mechanism is unknown . Overall, the genes overexpressed in activated NK cells confer not only potent cytotoxic ability but also immunomodulatory function to these activated NK cells . The gene expression profiling of NK cells in resting and stimulated states provide us with a better understanding of NK-cell function and improve our understanding of the molecular mediators underlying NK-cell activation.