Interactive effects of Na and K in killing by human natural killer cells

Electrolyte imbalance causes suppression of NK and T cell effector function in malignant ascites

BACKGROUND

Malignant ascites commonly occurs in advanced or recurrent stages of epithelial ovarian cancer during peritoneal carcinomatosis and is correlated with poor prognosis. Due to its complex composition of cellular and acellular components malignant ascites creates a unique tumor microenvironment, which mediates immunosuppression and promotes progression of disease. However, the immunosuppressive mechanisms remain poorly understood.

METHODS

In the present study, we explored the antitumor activity of healthy donor NK and T cells directed against ovarian cancer cells in presence of malignant ascites derived from patients with advanced or recurrent peritoneal carcinomatosis. A wide range of methods was used to study the effect of ascites on NK and T cells (FACS, ELISA, EliSpot, qPCR, Live-cell and confocal microscopy, Western blot and electrolyte flux assays). The ascites components were assessed using quantitative analysis (nephelometry, potentiometry and clinical chemistry) and separation methods (dialysis, ultracentrifugal filtration and lipid depletion).

RESULTS

Ascites rapidly inhibited NK cell degranulation, tumor lysis, cytokine secretion and calcium signaling. Similarly, target independent NK and T cell activation was impaired in ascites environment. We identified imbalanced electrolytes in ascites as crucial factors causing extensive immunosuppression of NK and T cells. Specifically, high sodium, low chloride and low potassium content significantly suppressed NK-mediated cytotoxicity. Electrolyte imbalance led to changes in transcription and protein expression of electrolyte channels and impaired NK and T cell activation. Selected inhibitors of sodium electrolyte channels restored intracellular calcium flux, conjugation, degranulation and transcript expression of signaling molecules. The levels of ascites-mediated immunosuppression and sodium/chloride/potassium imbalance correlated with poor patient outcome and selected molecular alterations were confirmed in immune cells from ovarian cancer patients.

CONCLUSION

Our data suggest a novel electrolyte-based mechanism of immunosuppression in malignant ascites of patients with peritoneal carcinomatosis. We show for the first time that the immunosuppression of NK cytotoxicity in coculture assays is correlated to patient poor survival. Therapeutic application of sodium channel inhibitors may provide new means for restoring immune cell activity in ascites or similar electrolyte imbalanced environments.

High-salt diet mediates interplay between NK cells and gut microbiota to induce potent tumor immunity

High-salt diet (HSD) modulates effector and regulatory T cell functions and promotes tissue inflammation in autoimmune diseases. However, effects of HSD and its association with gut microbiota in tumor immunity remain undefined. Here, we report that HSD induces natural killer (NK) cell–mediated tumor immunity by inhibiting PD-1 expression while enhancing IFNγ and serum hippurate. Salt enhanced tumor immunity when combined with a suboptimal dose of anti-PD1 antibody. While HSD-induced tumor immunity was blunted upon gut microbiota depletion, fecal microbiota transplantation (FMT) from HSD mice restored the tumor immunity associated with NK cell functions. HSD increased the abundance of Bifidobacterium and caused increased gut permeability leading to intratumor localization of Bifidobacterium, which enhanced NK cell functions and tumor regression. Intratumoral injections of Bifidobacterium activated NK cells, which inhibited tumor growth. These results indicate that HSD modulates gut microbiome that induces NK cell–dependent tumor immunity with a potential translational perspective.

Blocking KCa3.1 channels increases tumor cell killing by a subpopulation of human natural killer lymphocytes

Natural killer (NK) cells are large granular lymphocytes that participate in both innate and adaptive immune responses against tumors and pathogens. They are also involved in other conditions, including organ rejection, graft-versus-host disease, recurrent spontaneous abortions, and autoimmune diseases such as multiple sclerosis. We demonstrate that human NK cells express the potassium channels Kv1.3 and KCa3.1. Expression of these channels does not vary with expression levels of maturation markers but varies between adherent and non-adherent NK cell subpopulations. Upon activation by mitogens or tumor cells, adherent NK (A-NK) cells preferentially up-regulate KCa3.1 and non-adherent (NA-NK) cells preferentially up-regulate Kv1.3. Consistent with this different phenotype, A-NK and NA-NK do not display the same sensitivity to the selective KCa3.1 blockers TRAM-34 and NS6180 and to the selective Kv1.3 blockers ShK-186 and PAP-1 in functional assays. Kv1.3 block inhibits the proliferation and degranulation of NA-NK cells with minimal effects on A-NK cells. In contrast, blocking KCa3.1 increases the degranulation and cytotoxicity of A-NK cells, but not of NA-NK cells. TRAM-34, however, does not affect their ability to form conjugates with target tumor cells, to migrate, or to express chemokine receptors. TRAM-34 and NS6180 also increase the proliferation of both A-NK and NA-NK cells. This results in a TRAM-34-induced increased ability of A-NK cells to reduce in vivo tumor growth. Taken together, our results suggest that targeting KCa3.1 on NK cells with selective blockers may be beneficial in cancer immunotherapy.

Pharmacologic modulation of the immune interaction between cytotoxic lymphocytes and ventricular myocytes

Numerous studies have demonstrated that immune effector mechanisms cause serious heart diseases, among which are heart transplant rejection, myocarditis, and the resulting dilated cardiomyopathy, as well as Chagas' disease. Whereas different effectors of the immune system can affect cardiac function, this review primarily focuses on the immune damage caused by cytotoxic T lymphocytes. The immune attack staged by cytotoxic T lymphocytes is carried out by one of two distinct modes of lymphocytotoxicity: (a) secretion of lytic granules containing the pore-forming protein perforin and a family of serine proteases (i.e., granzymes) and (b) interaction between the lymphocyte Fas ligand and the target cell Fas receptor. Ventricular myocytes challenged by the immune system sustain diverse intracellular changes, among which the rise in intracellular calcium ([Ca2+]i) constitutes an important contributor to myocyte dysfunction. Hence, this [Ca2+]i rise, which does not necessarily result in apoptosis, can affect cardiac function directly and indirectly. Importantly, the final outcomes of these perturbations vary markedly and depend on intracellular circumstances such as the magnitude of the absolute rise in [Ca2+]i and its temporal and spatial determinants, the metabolic status of the myocyte, as well as a fine balance between pro-apoptotic and anti-apoptotic factors. In view of the central role of [Ca2+]i rise in immune-mediated myocyte dysfunction and possibly cell death, this review addresses three topics related to the immune assault on the heart: (a) [Ca2+]i rise in affected myocytes; (b) the source for the [Ca2+]i rise; and (c) pharmacologic modification of the immune-mediated [Ca2+]i rise.

Interaction of cytotoxic T lymphocytes and guinea pig ventricular myocytes. Pharmacological modulation by blocking K+ currents in cytotoxic T lymphocytes

Infiltrating cytotoxic T lymphocytes (CTLs) are important immune effectors that damage the myocardium during heart transplant rejection as well as in cardiomyopathy and Chagas' heart disease. We have previously shown that in an in vitro model of murine-derived peritoneal exudate CTL (PEL)-guinea pig ventricular myocyte interaction, PEL induced in conjugated myocytes reduction of resting membrane potential and action potential (AP) amplitude, shortening of AP duration, delayed afterdepolarizations (DADs), and myocyte contracture and destruction. Since these findings indicated that cytotoxicity was largely caused by [Ca2+]i overload, in the present study we tested the hypothesis that blocking the L-type Ca2+ current (ICa,L) in the myocyte will eliminate the trigger for Ca2+ release from intracellular stores and will reduce [Ca2+]i overload and subsequent myocyte deterioration. CoCl2 (3 mmol/L) prevented PEL-induced AP changes, induction of DADs, and myocyte destruction. Since verapamil (2 mumol/L) was ineffective, indicating that the CoCl2 protection was not due to block of ICa,L, we tested whether the different action of these Ca2+ channel blockers was due to their differential effect on the PEL's K+ current (IK), previously shown to participate in lymphocyte activation and cytotoxicity. In agreement with their protective efficacy, CoCl2 but not verapamil blocked IK in PELs, suggesting that this is the mechanism for the protection provided by CoCl2. To support this notion, we tested the effect of the scorpion-derived peptide margatoxin (10 nmol/L), a specific K+ channel blocker in lymphocytes, on PEL-myocyte interaction and on PEL's IK; margatoxin prevented PEL-induced cytotoxicity and also blocked IK in PEL. Based on these findings, an alternative modality for attenuating CTL-induced lymphocytotoxicity is proposed.

Opposite effects of amiloride and amiloride analogues on activation of natural killer cytotoxicity by the phorbol ester TPA and gamma-interferon

Amiloride, a K(+)-sparing diuretic used as an Na+/H+ exchange inhibitor, blocked the activation of human natural killer (NK) activity against K562 cells by either the phorbol ester TPA or gamma-interferon. However, this stimulation was not blocked by 5-(N,N-hexamethylene)amiloride, a potent inhibitor of Na+/H+ exchange. Spontaneous NK activity was inhibited by this amiloride analogue as well as by 5-(N-methyl-N-guanidinocarbonylmethyl) amiloride, another potent inhibitor of exchange, but only in concentrations 30-80 times higher than those used to inhibit Na+/H+ exchange. The analogue phenamil amiloride blocked NK activity in concentrations found to inhibit epithelial Na+ channels, whereas tetrodotoxin, the specific inhibitor of voltage-dependent Na+ channels, had no effect. These results indicate that Na+/H+ exchange is not essential either for spontaneous NK activity or for its activation by TPA and gamma-interferon. They also suggest the involvement of voltage-independent Na+ channels in NK activity.

Reduced calcium and inhibition of protein kinase C mimic the enhancement of ornithine decarboxylase activity of prolactin in Ambystoma tigrinum tissues

We previously reported that prolactin (PRL) could increase the activity of ornithine decarboxylase (ODC) in liver slices taken from larval tiger salamanders (Ambystoma tigrinum). This action of the hormone was inhibited by oxytocin (OT), the calcium ionophore A23187, and diacyglycerol (DG) and was duplicated by 10 microM verapamil (VML), a calcium channel blocker. Here, we expand these results to show that 1) a higher dose of VML (50 microM) produces an additive effect with PRL; 2) addition of small amounts of calcium (0.1 mM) to the liver culture medium blocks PRL action; 3) neither nifedipine (NIF), a different type of calcium channel blocker, nor EDTA alter PRL action; and 4) gossypol, a reported inhibitor of protein kinase C, mimics PRL action. Additionally, we show that PRL increases ODC activity in tiger salamander tail skin in vitro, a tissue previously demonstrated to be a PRL target tissue in this species. The same set of treatments which we have shown to modify PRL effects on ODC in liver slices affects PRL action in the tail skin in a parallel manner. Thus, the mechanism whereby PRL enhances ODC activity appears to be the same in both these tissues. These results are discussed in conjunction with the findings from similar studies using mammalian tissues in an attempt to assess the current picture of the mechanism of PRL action and the possible role of inositol phospholipid turnover, calcium, and protein kinase C in the action of this hormone.

Role of ion channels in lymphocytes

Ion channels, and ion fluxes in general, appear to regulate a wide variety of processes important to lymphocyte function in normal and disease states. These include resting ionic homeostasis and the more complex signaling events involved in activation, proliferation, cytotoxic function, and volume regulation. The wider application of patch-clamp and microfluorimetry techniques to lymphocytes has helped to clarify some issues and raised many more. It seems likely that rapid progress will be made in our understanding of these areas through a combination of immunological, biochemical, and electrophysiological approaches.