The effect of surgical stress and endotoxin-induced sepsis on the NK-cell activity, distribution and pulmonary clearance of YAC-1 and melanoma cells

Adoptive transfer of natural killer cells promotes the anti-tumor efficacy of T cells

The density of NK cells in tumors correlates positively with prognosis in many types of cancers. The average number of infiltrating NK cells is, however, quite modest (approximately 30 NK cells/sq.mm), even in tumors deemed to have a "high" density of infiltrating NK cells. It is unclear how such low numbers of tumor-infiltrating NK cells can influence outcome. Here, we used ovalbumin-expressing tumor cell lines and TCR transgenic, OVA-specific cytotoxic T lymphocytes (OT-I-CTLs) to determine whether the simultaneous attack by anti-tumor CTLs and IL-2-activated NK (A-NK) cells synergistically increases the overall tumor cell kill and whether upregulation of tumor MHC class-I by NK cell-derived interferon-gamma (IFNγ) improves tumor-recognition and kill by anti-tumor CTLs. At equal E:T ratios, A-NK cells killed OVA-expressing tumor cells better than OT-I-CTLs. The cytotoxicity against OVA-expressing tumor cells increased by combining OT-I-CTLs and A-NK cells, but the increase was additive rather than synergistic. A-NK cells adenovirally-transduced to produce IL-12 (A-NK^IL-12) produced high amounts of IFNγ. The addition of a low number of A-NK^IL-12 cells to OT-I-CTLs resulted in a synergistic, albeit modest, increase in overall cytotoxicity. Pre-treatment of tumor cells with NK cell-conditioned medium increased tumor MHC expression and sensitivity to CTL-mediated killing. Pre-treatment of CTLs with NK cell-conditioned medium had no effect on CTL cytotoxicity. In vivo, MHC class-I expression by OVA-expressing B16 melanoma lung metastases increased significantly within 24-48h after adoptive transfer of A-NK^IL-12 cells. OT-I-CTLs and A-NK^IL-12 cells localized selectively and equally well into OVA-expressing B16 lung metastases and treatment of mice bearing 7-days-old OVA-B16 lung metastases with both A-NK^IL-12 cells and OT-I-CTLs lead to a significant prolongation of survival. Thus, an important function of tumor-infiltrating NK cells may be to increase tumor cell expression of MHC class-I through secretion of IFNγ, to prepare them for recognition by tumor-specific CTLs.

Toll-like receptors expression and interferon-γ production by NK cells in human sepsis

Introduction

During the course of infection, natural killer (NK) cells contribute to innate immunity by producing cytokines, particularly interferon-gamma (IFN-γ). In addition to their beneficial effects against infection, NK cells may play a detrimental role during systemic inflammation, causing lethality during sepsis. Little is known on the immune status of NK cells in patients with systemic inflammatory response syndrome (SIRS) or sepsis in terms of cell surface markers expression and IFN-γ production.

Methods

We investigated 27 sepsis patients and 11 patients with non-infectious SIRS. CD56^bright and CD56^dim NK cell subsets were identified by flow cytometry and Toll-like receptor (TLR)2, TLR4, TLR9, CX3CR1, CD16 and CD69 expression were analyzed, as well as ex vivo IFN-γ production by NK cells in whole blood samples.

Results

We first showed that in NK cells from healthy controls, TLR2 and TLR4 expression is mainly intracellular, similarly to TLR9. Intracellular levels of TLR2 and TLR4, in both CD56^bright and CD56^dim NK cell subsets from sepsis patients, were increased compared to healthy subjects. In addition, the percentage of CD69⁺ cells was higher among NK cells of sepsis patients. No difference was observed for TLR9, CX3CR1, and CD16 expression. The ex vivo stimulation by TLR4 or TLR9 agonists, or whole bacteria in synergy with accessory cytokines (IL-15+IL-18), resulted in significant production of IFN-γ by NK cells of healthy controls. In contrast, for SIRS and sepsis patients this response was dramatically reduced.

Conclusions

This study reports for the first time an intracellular expression of TLR2 and TLR4 in human NK cells. Surface TLR4 expression allows discriminating sepsis and SIRS. Furthermore, during these pathologies, NK cells undergo an alteration of their immune status characterized by a profound reduction of their capacity to release IFN-γ.

NK cell tolerance to TLR agonists mediated by regulatory T cells after polymicrobial sepsis

As sensors of infection, innate immune cells are able to recognize pathogen-associated molecular patterns by receptors such as TLRs. NK cells present in many tissues contribute to inflammatory processes, particularly through the production of IFN-γ. They may display a protective role during infection but also a detrimental role during sterile or infectious systemic inflammatory response syndrome. Nevertheless, the exact status of NK cells during bacterial sepsis and their capacity directly to respond to TLR agonists remain unclear. The expression of TLRs in NK cells has been widely studied by analyzing the mRNA of these receptors. The aim of this study was to gain insight into TLR2/TLR4/TLR9 expression on/in murine NK cells at the protein level and determine if their agonists were able to induce cytokine production. We show, by flow cytometry, a strong intracellular expression of TLR2 and a low of TLR4 in freshly isolated murine spleen NK cells, similar to that of TLR9. In vitro, purified NK cells respond to TLR2, TLR4, and TLR9 agonists, in synergy with activating cytokines (IL-2, IL-15, and/or IL-18), and produce proinflammatory cytokines (IFN-γ and GM-CSF). Finally, we explored the possible tolerance of NK cells to TLR agonists after a polymicrobial sepsis (experimental peritonitis). For the first time, to our knowledge, NK cells are shown to become tolerant in terms of proinflammatory cytokines production after sepsis. We show that this tolerance is associated with a reduction of the CD27(+)CD11b(-) subset in the spleen related to the presence of regulatory T cells and mainly mediated by TGF-β.

Natural killer (NK) cells in antibacterial innate immunity: angels or devils?

Natural killer (NK) cells were first described as immune leukocytes that could kill tumor cells and soon after were reported to kill virus-infected cells. In the mid-1980s, 10 years after their discovery, NK cells were also demonstrated to contribute to the fight against bacterial infection, particularly because of crosstalk with other leukocytes. A wide variety of immune cells are now recognized to interact with NK cells through the production of cytokines such as interleukin (IL)-2, IL-12, IL-15 and IL-18, which boost NK cell activities. The recent demonstration that NK cells express pattern recognition receptors, namely Toll-like and nucleotide oligomerization domain (NOD)-like receptors, led to the understanding that these cells are not only under the control of accessory cells, but can be directly involved in the antibacterial response thanks to their capacity to recognize pathogen-associated molecular patterns. Interferon (IFN)-γ is the predominant cytokine produced by activated NK cells. IFN-γ is a key contributor to antibacterial immune defense. However, in synergy with other inflammatory cytokines, IFN-γ can also lead to deleterious effects similar to those observed during sepsis. Accordingly, as the main source of IFN-γ in the early phase of infection, NK cells display both beneficial and deleterious effects, depending on the circumstances.

Potential prophylactic measures against postoperative immunosuppression: could they reduce recurrence rates in oncological patients?

BACKGROUND

Removing the primary tumor is indispensable for eliminating the major pool of metastasizing cells, but the surgical procedure itself is suspected of promoting metastases. This adverse effect is attributed to several mechanisms acting in synergy, including mechanical release of tumor cells, enhanced angiogenesis, secretion of growth factors, and immunosuppression. Here we provide new insights into mechanisms of postoperative immunosuppression and assess the assumptions underlying the hypothesis that, by suppressing cell-mediated immunity (CMI), surgery may render the patient vulnerable to metastases that otherwise could have been controlled.

METHODS

An extensive review of relevant articles in English identified by using the MEDLINE database and cross-referencing.

RESULTS

Current literature suggests that (1) CMI can control minimal residual disease, especially if surgery is performed early; (2) major surgery transiently but markedly suppresses CMI through multiple mechanisms now better understood; (3) surgical stress promotes experimental metastasis through immunosuppression, but the clinical evidence remains indirect because of ethical limitations.

CONCLUSIONS

Minimizing postoperative immunosuppression seems feasible, may limit recurrence, and should be introduced into the broader array of considerations when planning oncological surgeries. In the short run, physicians could try to avoid immunosuppressive anesthetic approaches, inadvertent hypothermia, excessive blood transfusions, and untended postoperative pain. When feasible, minimally invasive surgery should be considered. In the long run, clinical trials should evaluate prophylactic measures, including perioperative immunostimulation and several antagonists to cytokines and hormones specified herein.

Prostaglandin e(2) suppresses NK activity in vivo and promotes postoperative tumor metastasis in rats

BACKGROUND

Prostaglandins (PGs) were shown in vitro to suppress several functions of cellular immunity. It is unclear, however, whether physiological levels of PGs can suppress cellular immunity in vivo and whether such suppression would compromise postoperative host resistance to metastasis.

METHODS

Fischer 344 rats were administered PGE(2) in doses (18 to 300 micro g/kg subcutaneously) that increased the serum levels approximately 2- to 4-fold. We then assessed the number and activity of circulating natural killer (NK) cells, as well as rats' resistance to experimental metastasis of a syngeneic NK-sensitive tumor (MADB106). To study whether endogenously released PGs after surgery compromise these indices, we tested whether laparotomy adversely affects them and whether a cyclooxygenase-synthesis inhibitor, indomethacin (4 mg/kg), attenuates these effects.

RESULTS

PGE(2) dose-dependently suppressed NK activity per NK cell and dose-dependently increased 4- and 24-hour MADB106 lung tumor retention (LTR); 240 micro g/kg of PGE(2) quadrupled the number of lung metastases counted 3 weeks later. Selective depletion of NK cells abrogated the promotion of LTR by PGE(2). Surgery significantly suppressed NK activity and increased MADB106 LTR, and indomethacin halved these effects without affecting nonoperated rats.

CONCLUSIONS

PGE(2) is a potent in vivo suppressor of NK activity, and its postoperative release may promote tumor recurrence.

Glucocorticoid involvement in suppression of NK activity following surgery in rats

We studied plasma factors mediating suppression of NK activity (NKA) following surgery. Plasma from operated rats suppressed NKA of splenocytes, leukocytes, and purified natural killer (NK) cells, and charcoal stripping nullified suppression. The glucocorticoid antagonist mifepristone prevented suppression, whereas blockers of reactive oxygen metabolites, opioids, catecholamines, prostaglandin-E2, and histamine did not. NKA dropped as corticosterone levels peaked postoperatively, and administration of relevant doses of corticosterone suppressed NKA. Inhibition of glucocorticoid synthesis prevented plasma from suppressing NKA but merely attenuated NKA suppression in operated rats. Thus, postoperative concentrations of corticosterone can directly suppress NKA but additional factors probably act in vivo.

Lymphocyte subset numbers depend on the bacterial origin of sepsis

OBJECTIVE

To determine the quantitative variances in peripheral blood lymphocyte subsets during sepsis, and their clinical significance.

METHODS

Peripheral blood lymphocyte subsets were enumerated in 32 non-surgical septic patients during the first 14 days of hospitalization; results from septic patients were compared with those from 34 healthy controls. Influences of the severity and the bacterial etiology of sepsis on changes in lymphocyte subsets were also assessed.

RESULTS

Significant decreases (P < 0.05) from normal values of CD4+, CD8+ and total T-lymphocytes were observed in septic patients, but the decline persisted only for CD4+ T-lymphocytes and natural killer (NK) cells for 3 and 7 days, respectively. In addition, the numbers of CD3+/DR+ lymphocytes were significantly elevated on day 14. There were no correlations between these alterations and the severity of sepsis. Gram-positive sepsis (n = 10), which was mainly due to Streptococcus pneumoniae and Staphylococcus aureus, caused prolonged decreases in CD4+, CD8+ and total T-lymphocytes, and a reduction in NK cells, that lasted for >or=14 days. Conversely, patients with sepsis due to Gram-negative pathogens (Neisseria meningitidis, n = 8; enterobacteria, n = 2) achieved full recovery of the subsets within 3 days. Moreover, the patients with Gram-negative sepsis demonstrated a significant increase in B-lymphocytes, and a rise in the numbers of CD3+/DR+ and CD4+ T-lymphocytes, which were more rapid than in patients with Gram-positive sepsis.

CONCLUSION

Our results indicate that Gram-positive sepsis causes stronger suppression of peripheral blood lymphocyte subsets in comparison to sepsis due to Gram-negative pathogens.

Mechanism of norepinephrine-mediated inhibition of human NK cytotoxic functions: inhibition of cytokine secretion, target binding, and programming for cytotoxicity

Norepinephrine (NE) has been shown to inhibit human peripheral blood-derived natural-killer (NK) cell cytotoxicity (NKCC) in vitro. We demonstrate in this study that NE not only inhibits IL-2-activated NKCC but antibody-dependent cellular cytotoxicity (ADCC) as well. NK cytotoxicity by purified NK cells against K562 (NKCC) and against Raji cells (ADCC) were inhibited by NE (1-100 microM) by more than 50% in a 4-h (51)Cr release assay. The mechanism underlying the inhibition has been examined. NK cytotoxicity is dependent on target recognition and formation of NK-target conjugates, and activation by IL-2 is dependent on the secretion of cytokines (such as TNF-alpha) by NK cells. We hypothesized that the inhibition of NK functions by NE may be due to disruption of NK-target conjugation, blocking programming for lysis, and/or inhibition of cytokine secretion. Pretreatment of human peripheral blood mononuclear cells (PBMC) with NE for 15 min significantly reduced the binding to K562 cells by CD16(+) NK lymphocytes. In the presence of K562 cells, NE down-regulated the expression of CD16 (FcgammaRIII) by human PBMC, an NK cell receptor responsible and necessary for ADCC and cytokine secretion. We also demonstrate that NE inhibited the IL-2-mediated up-regulation of the activation marker CD69. At concentrations of 10(-6) to 10(-5) M, NE inhibited TNF-alpha, IFN-gamma, and GM-CSF secretion by NK cells, which are essential for IL-2-driven NK maturation and functions. In addition, using single-cell analysis, NE pretreatment of lymphocytes reduced the frequency of killer cells in the NK-K562 conjugate population in a concentration-dependent manner, indicating an inhibition of the programming for lysis by NK cells. In summary, these data demonstrate that NE-induced inhibition of NK cytotoxicity is manifested at multiple levels, including a modification of NK cell receptor ligation to target cells, blockade of NK cytokine secretion necessary for NK maturation and differentiation, and inhibition of the target-induced activation of the cytotoxic mechanism(s) in NK cells. Thus, sympathetic activation, as often induced experimentally, may profoundly impair natural cellular immunity through varied measurable pathways.

Influence of surgery and endotoxin-induced sepsis combined on natural killer cell activity, oxidative burst of granulocytes and antigen presentation capability of monocytes

BACKGROUND

Cell mediated immunity is affected in the course of sepsis and following surgical stress. The natural killer (NK) cells, the granulocytes and the monocytes constitute the immediate unspecific cell mediated immunity. We therefore investigated the effect of surgery- and endotoxin-induced sepsis on NK cells, granulocytes and monocytes in a two-hit model.

METHODS

Three groups of 40 mice. Each group was divided into four groups of 10 mice. All the animals were anesthetized and subjected to either: laparotomy; treatment with Escherichia coli endotoxin i.p.; laparotomy followed 20 min later by endotoxin i.p.; or left untreated as a control group. In the first 40 mice the NK cell activity in the spleen and number of NK cells in the liver were measured, in the second the oxidative burst of granulocytes, and in the third the antigen presentation capacity of monocytes.

RESULTS

Endotoxin stimulated the NK cell activity and up-regulated the antigen presentation capability on monocytes. In contrast, surgical stress reduced the NK cell activity, the number of NK cells and down-regulated the antigen presentation capability on monocytes. After surgery, followed by administration of endotoxin, the oxidative burst of granulocytes was stimulated while antigen presentation capability on monocytes was down-regulated. Endotoxin prevented or reverted the postoperative suppression of NK cell activity.

CONCLUSION

Our two-hit model shows that some cell types of the unspecific immune system exhibit an excessive inflammatory response (NK cells, granulocytes) while specific functions of other cell types (monocytes) are simultaneously diminished. This diversity makes a potential therapeutic immunomodulation very complex as some cell types would need to be down-regulated while others need to be stimulated.