Fu-Dong Shi

Organ-specific features of natural killer cells

Natural killer (NK) cells can be swiftly mobilized by danger signals and are among the earliest arrivals at target organs of disease. However, the role of NK cells in mounting inflammatory responses is often complex and sometimes paradoxical. Here, we examine the divergent phenotypic and functional features of NK cells, as deduced largely from experimental mouse models of pathophysiological responses in the liver, mucosal tissues, uterus, pancreas, joints and brain. Moreover, we discuss how organ-specific factors, the local microenvironment and unique cellular interactions may influence the organ-specific properties of NK cells.

Natural killer cells determine the outcome of B cell-mediated autoimmunity.

Natural killer (NK) cells can affect the outcome of adaptive immune responses. NK cells, but not NK1.1+ T cells, were found to participate in the development of myasthenia gravis (a T cell–dependent, B cell– and antibody-mediated autoimmune disease) in C57BL/6 mice. The requirement for NK cells was reflected by the lack of a type 1 helper T cell response and antibodies to the acetylcholine receptor in both NK1.1+ cell–depleted and NK cell–deficient IL-18−/− mice. These findings establish a previously unrecognized link between NK cells and autoreactive T and B cells.

IL-18 Directs Autoreactive T Cells and Promotes Autodestruction in the Central Nervous System Via Induction of IFN-γ by NK Cells

IL-18 promotes NK cell and Th1 cell activity and may bridge innate and adaptive immune responses. Myelin oligodendrocyte glycoprotein (MOG) is a myelin component of the CNS and is a candidate autoantigen in multiple sclerosis. In the present study we show that IL-18-deficient (IL-18−/−) mice are defective in mounting autoreactive Th1 and autoantibody responses and are resistant to MOG35–55 peptide-induced autoimmune encephalomyelitis. IL-18 administration enhances the disease severity in wild-type mice and restores the ability to generate Th1 response in the IL-18−/− mice. This restoration was abrogated in NK cell-depleted mice, indicating that the action of IL-18 in promoting the generation of MOG-specific Th cells was dependent on NK cells. Furthermore, transfer of NK cells from recombinase-activating gene 1−/− mice, but not from recombinase-activating gene 1/IFN-γ−/− mice, rescued the defective Th1 responses in IL-18−/− mice and rendered IL-18−/− mice susceptible to the induction of autoimmune encephalomyelitis. Thus, IL-18 can direct autoreactive T cells and promote autodestruction in the CNS at least in part via induction of IFN-γ by NK cells.

Central nervous system (CNS)–resident natural killer cells suppress Th17 responses and CNS autoimmune pathology

Natural killer (NK) cells of the innate immune system can profoundly impact the development of adaptive immune responses. Inflammatory and autoimmune responses in anatomical locations such as the central nervous system (CNS) differ substantially from those found in peripheral organs. We show in a mouse model of multiple sclerosis that NK cell enrichment results in disease amelioration, whereas selective blockade of NK cell homing to the CNS results in disease exacerbation. Importantly, the effects of NK cells on CNS pathology were dependent on the activity of CNS-resident, but not peripheral, NK cells. This activity of CNS-resident NK cells involved interactions with microglia and suppression of myelin-reactive Th17 cells. Our studies suggest an organ-specific activity of NK cells on the magnitude of CNS inflammation, providing potential new targets for therapeutic intervention.

Differential Effects of IL-21 during Initiation and Progression of Autoimmunity against Neuroantigen

The cytokine IL-21 is closely related to IL-2 and IL-15, a cytokine family that uses the common γ-chain for signaling. IL-21 is expressed by activated CD4+ T cells. We examined the role of IL-21 in the autoimmune disease experimental autoimmune encephalomyelitis (EAE), an animal model for human multiple sclerosis. IL-21 administration before induction of EAE with a neuroantigen, myelin oligodendrocyte glycoprotein peptide 35-55, and adjuvant enhanced the inflammatory influx into the CNS, as well as the severity of EAE. Autoreactive T cells purified from IL-21-treated mice transferred more severe EAE than did the control encephalitogenic T cells. No such effects were observed when IL-21 was administered after EAE progressed. Additional studies demonstrated that IL-21 given before the induction of EAE boosted NK cell function, including secretion of IFN-γ. Depletion of NK cells abrogated the effect of IL-21. Therefore, IL-21, by affecting NK cells, has differential effects during the initiation and progression of autoimmune responses against neuroantigens.

Reciprocal regulation between natural killer cells and autoreactive T cells

The initiation and the progression of autoimmune diseases stem from complex interactions that involve cells of both the innate and the adaptive immune system. As we discuss here, natural killer (NK) cells, which are components of the innate immune system, can inhibit or promote the activation of autoreactive T cells during the initiation of autoimmunity. After they have been activated, autoreactive T cells contribute to the homeostatic contraction of NK-cell populations. The dynamic interaction between NK cells and autoreactive T cells might indicate the transition from the innate immune triggering of autoimmunity to the progressive phase of the disease. Understanding the mechanisms and signals that control the reciprocal regulation of NK cells and autoreactive T cells could have important implications for treatment in the clinic.

Natural killer cells in human autoimmunity

Natural killer (NK) cells are innate immune cells. Although NK cells are best characterized for their ability to control tumors and infections, recent data have indicated that they also are important regulatory cells by virtue of interactions with many types of immune and nonimmune cells. Thereby, they can affect the outcome of adaptive immune responses and maintain immune homeostasis. Thus, NK cells can either exacerbate or limit immune responses, including those to autoantigens. Here, we discuss current insights into the role of NK cells in human autoimmunity.

Fingolimod for the Treatment of Intracerebral Hemorrhage: A 2-Arm Proof-of-Concept Study

IMPORTANCE Pronounced inflammatory reactions occurring shortly after intracerebral hemorrhage (ICH) contribute to the formation and progression of perihematomal edema (PHE) and secondary brain injury. We hypothesized that modulation of brain inflammation reduces edema, thus improving clinical outcomes in patients with ICH. OBJECTIVE To investigate whether oral administration of fingolimod, a Food and Drug Administration-approved sphingosine 1-phosphate receptor modulator for multiple sclerosis, is safe and effective in alleviating PHE and neurologic deficits in patients with ICH. DESIGN, SETTING, AND PARTICIPANTS In this 2-arm, evaluator-blinded study, we included 23 patients with primary supratentorial ICH with hematomal volume of 5 to 30 mL. Clinical and neuroimaging feature-matched patients were treated with standard care with or without oral fingolimod. The study was conducted in Tianjin Medical University General Hospital, Tianjin, China. INTERVENTIONS All patients received standard management alone (control participants) or combined with fingolimod (FTY720, Gilenya), 0.5 mg, orally for 3 consecutive days. Treatment was initiated within 1 hour after the baseline computed tomographic scan and no later than 72 hours after the onset of symptoms. MAIN OUTCOMES AND MEASURES Neurologic status and hematomal and PHE volumes (Ev) and relative PHE, defined as Ev divided by hematomal volume, were monitored by clinical assessment and magnetic resonance imaging, respectively, for 3 months. RESULTS Patients treated with fingolimod exhibited a reduction of neurologic impairment compared with control individuals, regained a Glasgow Coma Scale score of 15 by day 7 (100% vs 50%, P = .01), and had a National Institutes of Health Stroke Scale score reduction of 7.5 vs 0.5 (P < .001). Neurologic functions improved in these patients in the first week coincident with a reduction of circulating lymphocyte counts. At 3 months, a greater proportion of patients receiving fingolimod achieved full recovery of neurologic functions (modified Barthel Index score range, 95-100; 63% vs 0%; P = .001; modified Rankin Scale score range, 0-1; 63% vs 0%; P = .001), and fewer reported ICH-related lung infections. Perihematomal edema volume and rPHE were significantly smaller in fingolimod-treated patients than in control individuals (Ev at day 7, 47 mL vs 108 mL, P = .04; Ev at day 14, 55 mL vs 124 mL, P = .07; rPHE at day 7, 2.5 vs 6.4, P < .001; rPHE at day 14, 2.6 vs 7.7, P = .003, respectively). We recorded no differences between groups in the occurrence of adverse events. CONCLUSIONS AND RELEVANCE In patients with small- to moderate-sized deep primary supratentorial ICH, administration of oral fingolimod within 72 hours of disease onset was safe, reduced PHE, attenuated neurologic deficits, and promoted recovery. The efficacy of fingolimod in preventing secondary brain injury in patients with ICH warrants further investigation in late-phase trials. TRIAL REGISTRATION clinicaltrials.gov Identifier:NCT02002390.

The Natural Killer Cell – Friend or Foe in Autoimmune Disease?

Autoimmune diseases are chronic conditions resulting from a loss of immunological tolerance to self‐antigens. Recent observations have supported an ever‐broader role for innate immune responses in directing and regulating adaptive immunity, including responses to self. This review summarizes recent findings supporting important functions of natural killer (NK) cells in regulating autoimmunity. A close survey of the current literature reveals multiple steps where NK cells can regulate inflammation and intervene in loss of self‐tolerance. Importantly, the findings also caution against inferring a similar role for NK cells in all autoimmune phenomena or during separate stages of the same disease. Indeed, NK cells may have different influences during the priming and the effector phases of disease. Hence, an increased understanding of the involvement of NK cells in inflammation and infection should provide new insights into the pathogenesis of autoimmune disease.

Nicotinic attenuation of central nervous system inflammation and autoimmunity.

The expression of nicotinic acetylcholine receptors by neurons, microglia, and astrocytes suggests possibly diverse mechanisms by which natural nicotinic cholinergic signaling and exposure to nicotine could modulate immune responses within the CNS. In this study, we show that nicotine exposure significantly delays and attenuates inflammatory and autoimmune responses to myelin Ags in the mouse experimental autoimmune encephalomyelitis model. In the periphery, nicotine exposure inhibits the proliferation of autoreactive T cells and alters the cytokine profile of helper T cells. In the CNS, nicotine exposure selectively reduces numbers of CD11c+ dendritic and CD11b+ infiltrating monocytes and resident microglial cells and down-regulates the expression of MHC class II, CD80, and CD86 molecules on these cells. The results underscore roles of nicotinic acetylcholine receptors and nicotinic cholinergic signaling in inflammatory and immune responses and suggest novel therapeutic options for the treatment of inflammatory and autoimmune disorders, including those that affect the CNS.