Natural Killer Cells In Lymph Nodes Research Articles

SIV-induced terminally differentiated adaptive NK cells in lymph nodes associated with enhanced MHC-E restricted activity

Natural killer (NK) cells play a critical understudied role during HIV infection in tissues. In a natural host of SIV, the African green monkey (AGM), NK cells mediate a strong control of SIVagm infection in secondary lymphoid tissues. We demonstrate that SIVagm infection induces the expansion of terminally differentiated NKG2alow NK cells in secondary lymphoid organs displaying an adaptive transcriptional profile and increased MHC-E-restricted cytotoxicity in response to SIV Env peptides while expressing little IFN-γ. Such NK cell differentiation was lacking in SIVmac-infected macaques. Adaptive NK cells displayed no increased NKG2C expression. This study reveals a previously unknown profile of NK cell adaptation to a viral infection, thus accelerating strategies toward NK-cell directed therapies and viral control in tissues.

Accumulation of Cytotoxic CD16+ NK Cells in Simian Immunodeficiency Virus-Infected Lymph Nodes Associated with In Situ Differentiation and Functional Anergy.

Recent evidence suggests that even in treated infections, human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) replication may continue in lymph nodes (LN), serving as a potential virus reservoir. Here we investigated the effects of lentivirus infection on natural killer (NK) cell frequencies, phenotypes, and functions in naive and acutely or chronically SIVmac239-infected rhesus macaques. Compared to that in naive animals, we observed a 3-fold-greater frequency of cytotoxic CD16(+) CD56(-) NK cells in LN of chronically infected macaques. However, NK cells did not appear to be trafficking to LN, as homing markers CD62L and CCR7 did not increase on circulating NK cells during infection. LN NK cells demonstrated enhanced cytotoxicity in acute infection, with 2-fold increases in perforin expression and 3-fold increases in CD107a expression following mitogen stimulation. Lysis of K562 cells by LN NK cells from acutely infected animals was greater than lysis by preinfection samples from the same animals. LN NK cells from chronically infected animals lysed K562 cells more efficiently than LN NK cells from uninfected animals, but importantly, surrogate markers of cytotoxicity in infected macaques were disproportionately greater than ex vivo killing. Furthermore, Tim-3, an indicator of activation and/or exhaustion, was upregulated 3-fold on LN NK cells in chronically infected animals. Collectively, these data suggest that LN NK cells are skewed toward a cytotoxic phenotype during SIV infection but may become dysfunctional and exhausted in chronic disease. The accumulation of CD16(+) CD56(-) NK cells in the SIV-infected lymph node without changes in NK homing to the LN could suggest that these cells are differentiating in situ. Surprisingly, this increase in frequency of the cytotoxic subset of NK cells is not accompanied by an increase of similar magnitude in the cytolytic function of LN lymphocytes. This functional modulation, together with the higher Tim-3 expression observed on LN NK cells isolated from chronically infected animals than on those from naive macaques, is indicative of an exhausted phenotype. This exhaustion could contribute to the robust replication of HIV and SIV in the LN during acute and chronic stages of infection, allowing the survival of infected cells and maintenance of a viral reservoir.

Chronic SIV infection induces differentiation and accumulation of cytotoxic CD16+ NK cells in lymph nodes followed by transmigration to the mucosae

Background Natural killer (NK) cells inhibit lentiviral replication both directly and indirectly, but substantial evidence also indicates HIV/SIV can induce NK cell dysfunction. NK cells can be subdivided based on expression of CD56 and CD16. In blood, cytotoxic CD16+ NK cells are the dominant subpopulation, while cytokine-secreting CD56+ and double-negative (DN) NK cells are the primary NK cells found in lymph nodes (LN). Furthermore, CD56+ and DN NK are thought to be precursor populations, whereas CD16+ NK cells are terminally differentiated. The effects of HIV/SIV infection on NK cell distribution, trafficking, and development are unclear. Methods

T-bet–dependent S1P5 expression in NK cells promotes egress from lymph nodes and bone marrow

During a screen for ethylnitrosourea-induced mutations in mice affecting blood natural killer (NK) cells, we identified a strain, designated Duane, in which NK cells were reduced in blood and spleen but increased in lymph nodes (LNs) and bone marrow (BM). The accumulation of NK cells in LNs reflected a decreased ability to exit into lymph. This strain carries a point mutation within Tbx21 (T-bet), which generates a defective protein. Duane NK cells have a 30-fold deficiency in sphingosine-1-phosphate receptor 5 (S1P5) transcript levels, and S1P5-deficient mice exhibit an egress defect similar to Duane. Chromatin immunoprecipitation confirms binding of T-bet to the S1pr5 locus. S1P-deficient mice exhibit a more severe NK cell egress block, and the FTY720-sensitive S1P1 also plays a role in NK cell egress from LNs. S1P5 is not inhibited by CD69, a property that may facilitate trafficking of activated NK cells to effector sites. Finally, the accumulation of NK cells within BM of S1P-deficient mice was associated with reduced numbers in BM sinusoids, suggesting a role for S1P in BM egress. In summary, these findings identify S1P5 as a T-bet–induced gene that is required for NK cell egress from LNs and BM.

NK Cells Induce Alloreactive Donor T Cell Apoptosis and Decrease Proliferation in GVHD Induction.

Natural Killer (NK) cells have the ability to suppress graft-versus-host disease (GVHD) while inducing a graft-versus-tumor response (GVT) during allogeneic bone marrow transplantation (BMT). Previous studies in allogeneic BMT models have shown NK cell trafficking to and proliferation in lymphoid organs and GVHD target organs, which are also sites of donor T cell trafficking. This study aims to investigate the impact of NK cells on alloreactive, GVHD-inducing donor T cells. Interleukin-2 activated allogeneic NK cells isolated from C57Bl6 (H–2b) or FVB (H–2q) animals were transplanted along with T cell-depleted bone marrow into lethally irradiated BALB/c (H–2d) mice, followed 2 days later by luciferase-expressing CD4+ and CD8+ conventional T cells from the same donor strain (NK+Tcon group). Control mice received lethal irradiation and T cell-depleted bone marrow on day 0, and luciferase-expressing T cells on day 2 after transplant (Tcon group). Bioluminescence imaging of NK+Tcon mice revealed a significantly lower T cell bioluminescent signal (p=0.03 for FVB into BALB/c on day 6) than from Tcon mice. CFSE proliferation analysis of alloreactive T cells on day 3 after transplant showed no significant change in the percent of donor T cells that have divided in the spleen, and only a slight decrease in the percent of T cells that have divided in the lymph nodes when NK cells are present. However, at this timepoint 82% of the proliferating cells have divided past the third generation, in contrast to 64% in the NK+Tcon mice. Donor T cells in both groups become equally activated in vivo, expressing similar levels of the early-activation marker CD69. T cells re-isolated from NK+Tcon animals at day 5 stained 2 to 10-fold higher for the TUNEL apoptosis marker than those from Tcon mice in the mesenteric and peripheral lymph nodes, respectively (p<0.0001). Additionally, decreased numbers of T cells were re-isolated from the peripheral lymph nodes in the NK+Tcon group as compared to the Tcon group. This increase in TUNEL staining was not seen when the transplanted NK cells were isolated from a perforin-deficient donor. This indicates that NK cells in lymph nodes use a perforin-dependent mechanism to increase apoptosis in proliferating, alloreactive donor T-cells, which are syngeneic to the transplanted NK cells. Donor T cells re-isolated from the lymph nodes of transplanted mice up-regulate the NKG2D ligand Rae1γ as compared to naïve T cells, as shown by FACS. This suggests that NK cells may cause direct lysis of alloreactive donor T cells in vivo during GVHD induction, mediated by the NK cell activating receptor NKG2D. This study provides crucial mechanistic information regarding the function of NK cells in suppressing GVHD.