The Impact Of Enriched Environment On Natural Killer-cell Proliferation And Terminal Maturation

Psychological stress is sufficiently profound to confer an important effect on a variety of diseases,including cancers,via modulating host’s immune system.However,little is known about the underlying mechanisms so far.Enriched Environment(EE)is a reliable experimental animal model of eustress or positive psychological stress.Exploring the effect of EE on immune effector cells will help further elucidate the impact of psychological stress on the immune system and related diseases,as well as the underlying mechanisms.Recent studies have demonstrated that EE-housed mice display a tumor-resistant phenotype.Our previous study revealed a critical role of NK cells,which are key anti-tumor immune effector cells,in EE-induced tumor inhibition.However,the regulatory effects of EE on NK cells and their mechanisms under physiological and pathological conditions have not been studied.Since the functions of NK cells(including the anti-tumor activity)depend on their terminal maturation process,the current study aims to investigate the impact of EE on NK-cell proliferation and terminal maturation in different lymphoid organs and peripheral blood in both intact and tumor-bearing mice.NK cells were classified into immature(CD27~+CD11b~-),intermediate mature(CD27~+CD11b~+)and mature(CD27~-CD11b~+)NK cells based on the expression of CD27 and CD11b.The proportions of NK cells with different maturation stages in bone marrow,peripheral blood,spleen and lymph node were analyzed by flow cytometry.The results revealed that EE significantly increased the proportion of mature NK cells in all examined tissues both in intact and tumor-bearing mice.Consistently,the expression level of Cxcr3,an immature marker of NK cells,was significantly decreased in splenic NK cells from EE-housed mice.These results suggested that EE promotes the terminal maturation of NK cells in central and peripheral lymphoid organs.Furthermore,in vivo Ed U incorporation assay revealed that EE significantly promoted the proliferation of non-mature NK cells in the bone marrow of intact mice.However,in tumor-bearing mice,EE specifically promoted the proliferation of non-mature NK cells in the spleen.Meanwhile,splenectomy can eliminate the tumor inhibitory effect of EE,suggesting that the proliferation and terminal maturation of splenic NK cells induced by EE may contribute to tumor-resistant phenotype of EE-housed mice.In order to further investigate the mechanisms of EE-induced phenotypic and functional changes of splenic NK cells in tumor-bearing mice,we performed the high-throughput cytokine antibody microarray of the spleens from mice EE and standard environment(SE)conditions.As a result,a total of 28 differentially expressed cytokines were identified.Among these differentially expressed cytokines,the expression of prolactin was changed most greatly with a 3.15-fold increase in the comparison of EE mice versus SE mice.Additionally,the“IL-17 signaling pathway”was significantly overrepresented in the KEGG enrichment analysis of the differentially expressed cytokines.It should be noted that prolactin and IL-17signaling pathway have been reported to exert an important modulatory impact on NK cells.In summary,our study demonstrated that EE-stimulated eustress confers a remarkable promoting effect on the proliferation and terminal maturation of NK cells.In particular,EE–induced NK-cell proliferation and maturation of splenic NK cells is critical for the tumor resistant phenotype of EE mice with mechanical involvement of the up-regulation of prolactin and modulation of IL-17 signaling in the spleen.