Activation of mu-opioid receptors are required for the conditioned enhancement of NK cell activity

Interactions Between Endogenous Opioids and the Immune System

The endogenous opioid system, which consists of opioid receptors and their ligands, is widely expressed in the nervous system and also found in the immune system. As a part of the body's defense machinery, the immune system is heavily regulated by endogenous opioid peptides. Many types of immune cells, including macrophages, dendritic cells, neutrophils, and lymphocytes are influenced by endogenous opioids, which affect cell activation, differentiation, proliferation, apoptosis, phagocytosis, and cytokine production. Additionally, immune cells also synthesize and secrete endogenous opioid peptides and participate peripheral analgesia. This chapter is structured into two sections. Part one focuses on immunoregulatory functions of central endogenous opioids; and part two describes how opioid peptide-containing immune cells participate in local analgesia.

Therapeutic Peptides for Treatment of Lung Diseases: Infection, Fibrosis, and Cancer

Various lung diseases endanger people's health. Side effects and pharmaceutical resistance complicate the treatment of acute lung injury, pulmonary fibrosis, and lung cancer, necessitating the development of novel treatments. Antimicrobial peptides (AMPs) are considered to serve as a viable alternative to conventional antibiotics. These peptides exhibit a broad antibacterial activity spectrum as well as immunomodulatory properties. Previous studies have shown that therapeutic peptides including AMPs had remarkable impacts on animal and cell models of acute lung injury, pulmonary fibrosis, and lung cancer. The purpose of this paper is to outline the potential curative effects and mechanisms of peptides in the three types of lung diseases mentioned above, which may be used as a therapeutic strategy in the future.

Methionine enkephalin (MENK) suppresses lung cancer by regulating the Bcl-2/Bax/caspase-3 signaling pathway and enhancing natural killer cell-driven tumor immunity

The aim of this study was to investigate how methionine enkephalin (MENK) regulates the biological behavior of lung cancer cells and to further explore its anti-lung cancer mechanisms in vitro and in vivo. The results showed that MENK enhanced the expression of opioid receptor (OGFr) and induced apoptosis of lung cancer cells by activating the Bcl-1/Bax/caspase-3 signaling pathway in vitro and in vivo. However, the regulatory effects of MENK disappeared after blockade of the OGFr. This confirmed that a prerequisite for the anti-tumor action of MENK is binding to OGFr. Additionally, we observed that MENK treatment enhanced the immunogenicity of lung cancer by enhancing the exposure of calreticulin and high mobility group box 1, and increasing the expression of NKG2D ligands. Further studies showed that MENK treatment increased the expression of natural killer (NK) cell-related cytokines such as granzyme B and interferon-γ and NK cell activation. Thus, we concluded that MENK might inhibit the proliferation of lung cancer cells by activating the Bcl-2/Bax/caspase-3 signaling pathway and enhancing immunogenicity and NK cell-driven tumor immunity.

Pavlovian Conditioning of Immunological and Neuroendocrine Functions

The phenomenon of behaviorally conditioned immunological and neuroendocrine functions has been investigated for the past 100 yr. The observation that associative learning processes can modify peripheral immune functions was first reported and investigated by Ivan Petrovic Pavlov and his co-workers. Their work later fell into oblivion, also because so little was known about the immune system’s function and even less about the underlying mechanisms of how learning, a central nervous system activity, could affect peripheral immune responses. With the employment of a taste-avoidance paradigm in rats, this phenomenon was rediscovered 45 yr ago as one of the most fascinating examples of the reciprocal functional interaction between behavior, the brain, and peripheral immune functions, and it established psychoneuroimmunology as a new research field. Relying on growing knowledge about efferent and afferent communication pathways between the brain, neuroendocrine system, primary and secondary immune organs, and immunocompetent cells, experimental animal studies demonstrate that cellular and humoral immune and neuroendocrine functions can be modulated via associative learning protocols. These (from the classical perspective) learned immune responses are clinically relevant, since they affect the development and progression of immune-related diseases and, more importantly, are also inducible in humans. The increased knowledge about the neuropsychological machinery steering learning and memory processes together with recent insight into the mechanisms mediating placebo responses provide fascinating perspectives to exploit these learned immune and neuroendocrine responses as supportive therapies, the aim being to reduce the amount of medication required, diminishing unwanted drug side effects while maximizing the therapeutic effect for the patient’s benefit.

Dynorphins in regulation of immune system functions

Dynorphins constitute a family of opioid peptides manifesting the highest affinity for κ-opiate receptors. Immune system cells are known to express a κ-receptor similar to that in the central nervous system, and as a consequence dynorphins are involved in the interaction between cells of the nervous and immune systems. In this review, data on dynorphin structure are analyzed and generalized, the κ-opiate receptor is characterized, and data on the regulation by dynorphins of functioning of the innate and adaptive immunity cells are summarized.

Induction on differentiation and modulation of bone marrow progenitor of dendritic cell by methionine enkephalin (MENK)

Methionine enkephalin (MENK), the endogenous neuropeptide, is known to exert direct effects on the neuroendocrine and the immune systems and participates in regulation of various functions of cells related to both the innate and adaptive immune systems. Dendritic cells (DCs) play important role in initiating and regulating T cell responses. The aim of this work is to investigate the effects of MENK on differentiation, maturation, and function of DCs derived from murine bone marrow progenitors (BM-derived DCs). Our result showed that MENK could induce BM-derived DCs to polarize predominantly to mDC subtype, rather than pDC both in vivo and in vitro, and this was in favor of Th1 response. BM-derived DCs, after treatment with MENK, up-regulated the expressions of MHC class II and key costimulatory molecules. Result by RT-PCR showed MENK could increase expressions of delta and kappa receptors on BM-derived DCs. Also MENK promoted BM-derived DCs to secret higher levels of proinflammatory cytokines of IL-12p70, TNF-α. Furthermore, differentiated BM-derived DCs treated with MENK displayed higher activity to induce allogeneic T cell proliferation and MENK also inhibited tumor growth in vivo and induced apoptosis of tumor cells in vitro. Thus, it is concluded that MENK could be an effective inducer of BM-derived DCs and might be a new therapeutic agent for cancer, as well as other immune handicapped disease. Also we may consider MENK as a potential adjuvant in vaccine preparation.

Comparison of stimulating effect on subpopulations of lymphocytes in human peripheral blood by methionine enkephalin with IL-2 and IFN-γ

The aim of this study was to investigate the effects of mechanisms of methionine enkephalin (MENK) on lymphocytes in human peripheral blood. We detected CD4+T cells, CD8+T cells, CD4+CD25+ regulatory T cells (Treg), dendritic cells (DCs), natural killer cells (NK), NKT cells and γδT cells before and after treatment with 10 (-12) M MENK, in cell culture by FCM and RT-PCR. Our findings show that MENK stimulating expansion of lymphocyte subpopulationns by inhibiting CD4+CD25+ regulatory T cells (Treg), which is unique discovery of our study. We may use MENK as a drug to treat cancer patients, whose immune systems are damaged by chemotherapy or radiotherapy.

Association of polymorphism in the human mu-opioid receptor OPRM1 gene with proinflammatory cytokine levels and health perception

Recent studies in psychoneuroimmunology have indicated that proinflammatory cytokines cause several diseases and behaviors that overlap symptomatically with depression. It is known that the endogenous opioid peptide beta-endorphin regulates proinflammatory cytokine secretion from peripheral immune cells via mu-opioid receptor-dependent mechanisms. Therefore, it is possible that the functional polymorphism of the mu-opioid receptor gene (OPRM1, SNP: A118G) influences peripheral circulating proinflammatory cytokine levels and the health-related quality of life (QOL) even in healthy populations. In this study, we compared the serum concentrations of several proinflammatory cytokines (interleukin-2 (IL-2), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma)) and the health-related QOL between OPRM1 genotypes. Interestingly, serum concentrations of IL-6, TNF-alpha, and IFN-gamma were significantly lower and the general health score was significantly higher in carriers of the G allele, who show a strong binding of beta-endorphin to the mu-opioid receptor as compared to individuals without the G allele. Correlation analysis indicated that the general health score was negatively correlated with the IL-6 serum concentration. These results suggest that the sensitive endogenous opioid system in carriers of the G allele may suppress proinflammatory cytokine secretion from peripheral immune cells; consequently, it may influence the health perception.

The conditioned enhancement of neutrophil activity is catecholamine dependent

Neutrophil activity was elevated in the conditioned mice for the first time through an established conditioned training process. Catecholamines were proved to be important in the regulation of this conditioned innate immunity. In the study, the camphor odor (as the conditioned stimulus, CS) and poly I: C (as the unconditioned stimulus, US) was used to conditionally elevate the activity of the splenic neutrophils. The mechanism(s) responsible for the conditioned enhancement of neutrophil activity was further investigated using the neurochemical blocking assay and immunohistochemical analysis. Results showed that the neutrophil activity was significantly enhanced through the conditioned training process; both reserpine and 6-hydroxydopamine (6-OHDA) significantly blocked this conditioned innate immunity at the conditioned recall stage. Dexamethasone (Dex), however, showed no effect on the conditioned neutrophil response. Tyrosine hydroxylase (TH)-positive cells significantly increased in the locus coeruleus (LC), hypothalamus, and cortex but not in the spleen of the conditioned animals. These results indicate that during the conditioned recall stage, the brain signals the splenic neutrophils via the sympathetic nervous system (SNS) by releasing the peripheral catecholamines in spleen. The activation of the SNS, on the other hand, is also under the influence of catecholamines released in the LC. The hypothalamic pituitary (HP) axis, on the other hand, plays no role in the regulation of the conditioned neutrophil response.

Opioids as modulators of cell death and survival--unraveling mechanisms and revealing new indications

Opioids are powerful analgesics but also drugs of abuse. Because opioid addicts are susceptible to certain infections, opioids have been suspected to suppress the immune response. This was supported by the finding that various immune-competent cells express opioid receptors and undergo apoptosis when treated with opioid alkaloids. Recent evidence suggests that opioids may also effect neuronal survival and proliferation or migrating properties of tumor cells. A multitude of signaling pathways has been suggested to be involved in these extra-analgesic effects of opioids. Growth-promoting effects were found to be mediated through Akt and Erk signaling cascades. Death-promoting effects have been ascribed to inhibition of nuclear factor-kappaB, increase of Fas expression, p53 stabilization, cytokine and chemokine release, and activation of nitric oxide synthase, p38, and c-Jun-N-terminal kinase. Some of the observed effects were inhibited with opioid receptor antagonists or pertussis toxin; others were unaffected. It is still unclear whether these properties are mediated through typical opioid receptor activation and inhibitory G-protein-signaling. The present review tries to unravel controversial findings and provides a hypothesis that may help to integrate diverse results.

Cholinergic and serotonergic activities are required in triggering conditioned NK cell response

The purpose of the study was to examine the importance of the cholinergic system in triggering the conditioned NK cell response. The fact that serotonergic system can modulate cholinergic functions suggested that it might be involved in conditioned NK cell response. To evaluate the potential pathways, cholinergic and serotonergic antagonists were applied centrally at either the conditioned association or recall stage, to interfere with the conditioned NK cell response. The results showed that both the cholinergic and serotonergic systems were necessary for eliciting the conditioned enhancement of NK cell activity. Involvements of the two systems were found to be critical for establishing the conditioned association and recall of the conditioned response. The blocks are believed to be receptor mediated. The receptors identified to be involved in the regulation of the conditioned NK cell response were: M(1), M(2) and M(3) muscarinic; nicotinic; 5 HT(1) and 5 HT(2) receptors.

Immune deviation following stress odor exposure: role of endogenous opioids

Olfactory cues can alter immune function. BALB/c mice exposed to odors produced by footshock stressed donor mice have increased antibody responses and increased splenic interleukin (IL)-4 production following immunization relative to recipients of odors from unstressed animals. Here we document that exposure to stress odors results in analgesia that is blocked by the non-selective opioid receptor antagonist naltrexone. The stress odor-induced increase in antigen-driven IL-4 and antibody is also blocked by oral administration of naltrexone. Thus, we provide evidence that immune deviation can occur following a psychosocial stressor, and that the deviation appears to be mediated by endogenous opioid production.

Psychoneuroendocrine immunology: perception of stress can alter body temperature and natural killer cell activity

Psychoimmunology has been credited with using the mind as a way to alter immunity. The problem with this concept is that many of the current psychoimmunology techniques in use are aimed at alleviating stress effects on the immune system rather than at direct augmentation of immunity by the brain. Studies in animals provide a model that permits us to approach the difficulties associated with gaining an understanding of the CNS-immune system connection. A particular advantage of using animals over humans is that psychological and social contributions play a less prominent role for animals than for human subjects, since the animals are all inbred and reared under identical controlled conditions. If the insightful information provided by animal studies is correct, then psychotherapy for the treatment of diseases might be made more effective if some aspect of this knowledge is included in the design of the treatment. We emphasize conditioning as a regimen and an acceptable way to train the brain to remember an output pathway to raise immunity. We propose that a specific drug or perception (mild stress, represented by rotation, total body heating or handling) could substitute and kindle the same output pathway without the need for conditioning. If this view is correct, then instead of using conditioning, it may be possible to use an antigen to activate desired immune cells, and substitute a drug or an external environmental sensory stimulus (perception) to energize the output pathway to these cells. Alternatively, monitoring alterations of body temperature in response to a drug or perception might allow us to follow how effectively the brain is performing in altering immunity. Studies with animals suggest that there are alternative ways to use the mind to raise natural or acquired immunity in man.

Involvement of catecholamines in recall of the conditioned NK cell response

The primary goal of the study was to identify the types of catecholamines and the associated receptors which might be involved in the recall of the conditioned NK cell response. Specific catecholamine receptor antagonists were selected to block the conditioned NK cell response at the recall step. The regional contents of dopamine (DA), norepinephrine (NE), and epinephrine were determined in the brain of the conditioned animals by using the high performance liquid chromatography with electrochemical detection (HPLC/ED). Results showed that pre-disruption of the central alpha1-, alpha2-, beta1-, beta2-, D1-, or D2-receptors at the conditioned recall stage, interrupted the conditioned enhancement in NK cell activity. The NE contents at the cerebellum, and DA contents at the striatum and hippocampus, were significantly higher in the brain of the conditioned animals when compared to that of the control animals. These information indicated the possible roles of the central noradrenergic and dopaminergic systems in regulating the recall of the conditioned NK cell response.

Enkephalin receptors and receptor-mediated signal transduction in cultured human lymphocytes

Enkephalins are opioid peptides that bridge the neuroendocrine and immune systems. Using flow cytometry and a fluorescein conjugate of the endogenous pentapeptide methionine-enkephalin (ME), we have identified enkephalin receptors on cultured human lymphocytes. Cell surface recognition sites that bound ME with high affinity and specificity were detected for NALM 6 (pre-B acute lymphoblastic leukemia) and Jurkat (T lymphoma) cells. Brain-like enkephalin receptors were measured for these lymphocytes using conventional radioligand-receptor assays and the highly delta opioid receptor-selective enkephalin analog [3H]DPDPE. Upon activation, the lymphocyte enkephalin receptors transmitted signals that enhanced the accumulation of intracellular cAMP. These studies provide evidence that cultured human lymphocytes of the B (NALM 6 cells) and T (Jurkat cells) lineages express functional enkephalin receptors and suggest that such receptors may be instrumental in the lymphocyte response to opioid peptides and alkaloids.