Opioid modulation of immune responses: effects on phagocyte and lymphoid cell populations

Salvinorin A has antiinflammatory and antinociceptive effects in experimental models of colitis in mice mediated by KOR and CB1 receptors

BACKGROUND

Salvinorin A (SA) has a potent inhibitory action on mouse gastrointestinal (GI) motility and ion transport, mediated primarily by kappa-opioid receptors (KOR). The aim of the present study was to characterize possible antiinflammatory and antinociceptive effects of SA in the GI tract of mice.

METHODS

Colonic damage scores and myeloperoxidase activity were determined after intraperitoneal (i.p.), intracolonic (i.c.), and oral (p.o.) administration of SA using the trinitrobenzene sulfonic acid (TNBS) and dextran sodium sulfate (DSS) models of colitis in mice. Additionally, KOR, cannabinoid (CB)1, and CB2 western blot analysis of colon samples was performed. The antinociceptive effect of SA was examined based on the number of behavioral responses to i.c. instillation of mustard oil (MO).

RESULTS

The i.p. (3 mg/kg, twice daily) and p.o. (10 mg/kg, twice daily) administration of SA significantly attenuated TNBS and DSS colitis in mice. The effect of SA was blocked by KOR antagonist nor-binaltorphimine (10 mg/kg, i.p.). Western blot analysis showed no influence of SA on KOR, CB1, or CB2 levels. SA (3 mg/kg, i.p. and 10 mg/kg, i.c.) significantly decreased the number of pain responses after i.c. instillation of MO in the vehicle- and TNBS-treated mice. The antinociceptive action of SA was blocked by KOR and CB1 antagonists. The analgesic effect of i.c. SA was more potent in TNBS-treated mice compared to controls.

CONCLUSIONS

Our results suggest that the drugs based on the structure of SA have the potential to become valuable antiinflammatory or analgesic therapeutics for the treatment of GI diseases.

Morphine induces splenocyte trafficking into the CNS

Opioids significantly alter functional responses of lymphocytes following activation. The opiate Morphine, alters the Th1 to Th2 response and modulates functional responses such as cytolytic activity and T-cell proliferation. Although there has been extensive research involving morphine's effects on lymphocytes, little is known about the effects morphine has on lymphocyte trafficking. The objective of the study was to use in vivo bioluminescent imaging to determine morphine's effect on the trafficking pattern of splenocytes systemically and into the CNS either in a naïve state or following a neuroinflammatory stimulus. A neuroinflammatory response was induced by intracerebrally administering a DNA IFN-γ DNA plasmid into morphine-dependent or placebo wildtype mice. Mice with or without a neurostimulus received adoptively transferred firefly luciferase transgenic splenocytes and imaged. Morphine dependence significantly altered the inherent ability of splenocytes to traffic into the spleen, and lead to non-directed chaotic trafficking throughout the animal, including into the CNS. The morphine-mediated effects on trafficking were blocked by the antagonist naltrexone. Morphine dependence intensified splenocyte infiltration into the CNS following neuroinflammation induced by IFN-γ gene transfer. The study precented determined that morphine severely altered the ability of non-activated splenocytes to home to the spleen, inducing extrasplenic trafficking thoughout the animal. In addition to altering the ability of naive splenocyte to traffic to the spleen, this study demonstrated that morphine profoundly exacerbated lymphocyte infiltration into the CNS following a neurostimulus.

Interactive Effects of Morphine on HIV Infection: Role in HIV-Associated Neurocognitive Disorder

HIV epidemic continues to be a severe public health problem and concern within USA and across the globe with about 33 million people infected with HIV. The frequency of drug abuse among HIV infected patients is rapidly increasing and is another major issue since injection drug users are at a greater risk of developing HIV associated neurocognitive dysfunctions compared to non-drug users infected with HIV. Brain is a major target for many of the recreational drugs and HIV. Evidences suggest that opiate drug abuse is a risk factor in HIV infection, neural dysfunction and progression to AIDS. The information available on the role of morphine as a cofactor in the neuropathogenesis of HIV is scanty. This review summarizes the results that help in understanding the role of morphine use in HIV infection and neural dysfunction. Studies show that morphine enhances HIV-1 infection by suppressing IL-8, downregulating chemokines with reciprocal upregulation of HIV coreceptors. Morphine also activates MAPK signaling and downregulates cAMP response element-binding protein (CREB). Better understanding on the role of morphine in HIV infection and mechanisms through which morphine mediates its effects may help in devising novel therapeutic strategies against HIV-1 infection in opiate using HIV-infected population.

Rodent models of HAND and drug abuse: exogenous administration of viral protein(s) and cocaine

Humans and chimpanzees are the natural hosts for HIV. Non-human primate models of SIV/SHIV infection in rhesus, cynomologus and pigtail macaques have been used extensively as excellent model systems for pathogenesis and vaccine studies. However, owing to the variability of disease progression in infected macaques, a phenomenon identical to humans, coupled with their prohibitive costs, there exists a critical need for the development of small-animal models in which to study the untoward effects of HIV-1 infection. Owing to the fact that rodents are not the natural permissive hosts for lentiviral infection, development of small animal models for studying virus infection has used strategies that circumvent the steps of viral entry and infection. Such strategies involve overexpression of toxic viral proteins, SCID mice engrafted with the human PBLs or macrophages, and EcoHIV chimeric virus wherein the gp120 of HIV-1 was replaced with the gp80 of the ecotropic murine leukemia virus. Additional strategy that is often used by investigators to study the toxic effect of viral proteins involves direct stereotactic injection of the viral protein(s) into specific brain regions. The present report is a compilation of the applications of direct administration of Tat into the striatum to mimic the effects of the viral neurotoxin in the CNS. Added advantage of this model is that it is also amenable to repeated intraperitoneal cocaine injections, thereby allowing the study of the additive/synergistic effects of both the viral protein and cocaine. Such a model system recapitulates aspects of HAND in the context of drug abuse.

Mu opioid receptor activation modulates Toll like receptor 4 in murine macrophages

Opioids have been shown to affect both innate and adaptive immunity. We previously showed that morphine affects the macrophage production of pro-inflammatory cytokines after LPS in a NFkB dependent manner. Toll like receptors (TLRs) play a crucial role in the signaling pathways which lead to NFkB activation. TLR4 is considered the Lipopolysaccaride (LPS) receptor. The data here presented show that, in murine macrophages, morphine impacts on the immune function acting on the early step of pathogen recognition. Morphine, when added to RAW 264.7 cells and when injected into mice (s.c. 20mg/kg) is in fact able to decrease TLR4 both at mRNA and protein level in RAW cells and peritoneal macrophages. In the same cells, the mu opioid receptor (MOR) antagonist Naltrexone increases TLR4 levels, thus suggesting a role of the endogenous opioid system in TLR4 regulation. The effect of the two drugs is moreover lost in case of co-administration. Experiments with MOR KO mice and with DAMGO (MOR specific agonist) confirm that the effect of morphine on TLR4 mRNA in peritoneal macrophages is due to the MOR activation. Moreover the effect on TLR4 is blocked by PTX thus indicating the involvement of a G(i) protein after MOR binding. This work unveils a clear link between MOR activation and TLR4, suggesting a new possible mechanism at the basis of the peripheral immunosuppressive effect of opioids.

Morphine decreases bacterial phagocytosis by inhibiting actin polymerization through cAMP-, Rac-1-, and p38 MAPK-dependent mechanisms

Morphine increases the susceptibility to opportunistic infection by attenuating bacterial clearance through inhibition of Fcγ receptor (FcgR)-mediated phagocytosis. Mechanisms by which morphine inhibits this process remain to be investigated. Actin polymerization is essential for FcgR-mediated internalization; therefore, disruption of the signaling mechanisms involved in this process is detrimental to the phagocytic ability of macrophages. To our knowledge, this study is the first to propose the modulation of actin polymerization and upstream signaling effectors [cAMP, Rac1-GTP, and p38 mitogen-activated protein kinase (MAPK)] as key mechanisms by which morphine leads to inhibition of pathogen clearance. Our results indicate that long-term morphine treatment in vitro and in vivo, through activation of the μ-opioid receptor, leads to an increase in intracellular cAMP, activation of protein kinase A, and inhibition of Rac1-GTPase and p38 MAPK, thereby attenuating actin polymerization and reducing membrane ruffling. Furthermore, because of long-term morphine treatment, FcgR-mediated internalization of opsonized dextran beads is also reduced. Morphine's inhibition of Rac1-GTPase activation is abolished in J774 macrophages transfected with constitutively active pcDNA3-EGFP-Rac1-Q61L plasmid. Dibutyryl-cAMP inhibits, whereas H89 restores, activation of Rac-GTPase and abolishes morphine's inhibitory effect, implicating cAMP as the key effector in morphine's modulation of actin polymerization. These findings indicate that long-term morphine treatment, by increasing intracellular cAMP and activating protein kinase A, leads to inhibition of Rac1-GTPase and p38 MAPK, causing attenuation of actin polymerization, FcgR-mediated phagocytosis, and decreased bacterial clearance.

Role of the mu-opioid receptor in opioid modulation of immune function

Endogenous opioids are synthesized in vivo to modulate pain mechanisms and inflammatory pathways. Endogenous and exogenous opioids mediate analgesia in response to painful stimuli by binding to opioid receptors on neuronal cells. However, wide distribution of opioid receptors on tissues and organ systems outside the CNS, such as the cells of the immune system, indicate that opioids are capable of exerting additional effects in the periphery, such as immunomodulation. The increased prevalence of infections in opioid abuser-based epidemiological studies further highlights the immunosuppressive effects of opioids. In spite of their many debilitating side effects, prescription opioids remain a gold standard for treatment of chronic pain. Therefore, given the prevalence of opioid use and abuse, opioid-mediated immune suppression presents a serious concern in our society today. It is imperative to understand the mechanisms by which exogenous opioids modulate immune processes. In this review, we will discuss the role of opioid receptors and their ligands in mediating immune-suppressive functions. We will summarize recent studies on direct and indirect opioid modulation of the cells of the immune system, as well as the role of opioids in exacerbation of certain disease states.

NOP Receptor Ligands as Potential Agents for Inflammatory and Autoimmune Diseases

Nociceptin/orphanin FQ (N/OFQ) is a seventeen-amino acid peptide that is the endogenous ligand of a G-protein-coupled receptor (NOP). Various immune cells express the precursor protein and secrete N/OFQ as well as display binding sites for this peptide. The functional capacity of NOP receptor was demonstrated in vitro and in vivo studies by the ability of N/OFQ to induce chemotaxis of immune cells, to regulate the expression of cytokines and other inflammatory mediators, and to control cellular and humoral immunity. In this context, N/OFQ could modulate the outcome of some inflammatory diseases, such as sepsis and autoimmune pathologies by mechanisms not clearly elucidated yet. In fact, human body fluid revealed increased levels of N/OFQ under sepsis, arthritis, and Parkinson's diagnose. Preclinical studies pointed to the blockade of NOP receptor signaling as successful in treating these experimental conditions. Further preclinical and clinical studies are required to investigate the potential of NOP ligands in treating inflammatory diseases.

Nonopioid effect of β-endorphin

This review presents the generalized literature data and the results of our own research of the nonopioid effect of β-endorphin, an opioid neuropeptide interacting not only with opioid but also with nonopioid (insensitive to the opioid antagonist naloxone) receptors. The roles of the hormone and its receptors in regulation of the immune, nervous, and endocrine systems are discussed. The effect of neuromediator on the immune system mediated by both opioid and nonopioid receptors is considered in detail. The data on distribution and function of the nonopioid β-endorphin receptor in human and animal organisms are presented. All available data on the characteristics of the nonopioid β-endorphin receptor obtained by means of radioligand analysis are given. The discussed information is supposed to extend our conceptions of the role of β-endorphin in mammals and to be of extensive use in medicine and pharmacology.

Morphine and tumor growth and metastasis

Morphine is an analgesic widely used to alleviate cancer pain. In addition, the perioperative management of pain in cancer surgery patients most often includes opioids. However, there are reports that these drugs may alter cancer recurrence or metastasis. Several mechanisms have been proposed, such as the modulation of the immune response or cellular pathways that control the survival and migratory behavior of cancer cells. The published literature, however, presents some discrepancies, with reports suggesting that opioids may either promote or prevent the spread of cancer. It is of great importance to determine whether opioids, in particular the most widely used, morphine, may increase the risk of metastasis when used in cancer surgery. This review examines the available data on the effects of morphine which influence cancer metastasis or recurrence, including immunomodulation, tumor cell aggressiveness, and angiogenesis, with special emphasis on recently published clinical and laboratory based studies. We further discuss the parameters that may explain the difference between reports on the effects of morphine on cancer.

The role of morphine in regulation of cancer cell growth

Morphine is considered the "gold standard" for relieving pain and is currently one of the most effective drugs available clinically for the management of severe pain associated with cancer. In addition to its use in the treatment of pain, morphine appears to be important in the regulation of neoplastic tissue. Although morphine acts directly on the central nervous system to relieve pain, its activities on peripheral tissues are responsible for many of the secondary complications. Therefore, understanding the impact, other than pain control, of morphine on cancer treatment is extremely important. The effect of morphine on tumor growth is still contradictory, as both growth-promoting and growth-inhibiting effects have been observed. Accumulating evidence suggests that morphine can affect proliferation and migration of tumor cells as well as angiogenesis. Various signaling pathways have been suggested to be involved in these extra-analgesic effects of morphine. Suppression of immune system by morphine is an additional complication. This review provides an update on the influence of morphine on the growth and migration potential of tumor cells.

Opioid drug abuse and modulation of immune function: consequences in the susceptibility to opportunistic infections

Infection rate among intravenous drug users (IDU) is higher than the general public, and is the major cause of morbidity and hospitalization in the IDU population. Epidemiologic studies provide data on increased prevalence of opportunistic bacterial infections such as TB and pneumonia, and viral infections such as HIV-1 and hepatitis in the IDU population. An important component in the intravenous drug abuse population and in patients receiving medically indicated chronic opioid treatment is opioid withdrawal. Data on bacterial virulence in the context of opioid withdrawal suggest that mice undergoing withdrawal had shortened survival and increased bacterial load in response to Salmonella infection. As the body of evidence in support of opioid dependency and its immunosuppressive effects is growing, it is imperative to understand the mechanisms by which opioids exert these effects and identify the populations at risk that would benefit the most from the interventions to counteract opioid immunosuppressive effects. Thus, it is important to refine the existing animal model to closely match human conditions and to cross-validate these findings through carefully controlled human studies. Better understanding of the mechanisms will facilitate the search for new therapeutic modalities to counteract adverse effects including increased infection rates. This review will summarize the effects of morphine on innate and adaptive immunity, identify the role of the mu opioid receptor in these functions and the signal transduction activated in the process. The role of opioid withdrawal in immunosuppression and the clinical relevance of these findings will also be discussed.

Cocaine and HIV-1 interplay: molecular mechanisms of action and addiction

Human immunodeficiency virus (HIV) infection is now being driven by drug-abusing populations. Epidemiological studies on drug abusers with AIDS link abuse of cocaine, even more than other drugs, to increased incidence of HIV seroprevalence and progression to AIDS. Both cell culture and animal studies demonstrate that cocaine can both potentiate HIV replication and can potentiate HIV proteins to cause enhanced glial cell activation, neurotoxicity, and breakdown of the blood-brain barrier. Based on the ability of both HIV proteins and cocaine to modulate NMDA receptor on neurons, NMDA receptors have been suggested as a common link underlying the crosstalk between drug addiction and HIV infection. While the role of dopamine system as a major target of cocaine cannot be overlooked, recent studies on the role of sigma receptors in mediating the effects of cocaine in both cell and organ systems warrants a deeper understanding of their functional role in the field. In this review, recent findings on the interplay of HIV infection and cocaine abuse and their possible implications in mode of action and/or addiction will be discussed.

Protein kinase Czeta mediates micro-opioid receptor-induced cross-desensitization of chemokine receptor CCR5

We have previously shown that the μ-opioid receptor (MOR) is capable of mediating cross-desensitization of several chemokine receptors including CCR5, but the biochemical mechanism of this process has not been fully elucidated. We have carried out a series of functional and biochemical studies and found that the mechanism of MOR-induced cross-desensitization of CCR5 involves the activation of PKCζ. Inhibition of PKCζ by its pseudosubstrate inhibitor, or its siRNA, or dominant negative mutants suppresses the cross-desensitization of CCR5. Our results further indicate that the activation of PKCζ is mediated through a pathway involving phosphoinositol-dependent kinase-1 (PDK1). In addition, activation of MOR elevates the phosphorylation level and kinase activity of PKCζ. The phosphorylation of PKCζ can be suppressed by a dominant negative mutant of PDK1. We observed that following MOR activation, the interaction between PKCζ and PDK1 is immediately increased based on the analysis of fluorescent resonance energy transfer in cells with the expression of PKCζ-YFP and PDK1-CFP. In addition, cells expressing PKCζ kinase motif mutants (Lys-281, Thr-410, Thr-560) fail to exhibit full MOR-induced desensitization of CCR5 activity. Taken together, we propose that upon DAMGO treatment, MOR activates PKCζ through a PDK1-dependent signaling pathway to induce CCR5 phosphorylation and desensitization. Because CCR5 is a highly proinflammatory receptor, and a critical coreceptor for HIV-1, these results may provide a novel approach for the development of specific therapeutic agents to treat patients with certain inflammatory diseases or AIDS.

Surgery induced immunosuppression

Surgery and anaesthesia result in a variety of metabolic and endocrine responses, which result in a generalised state of immunosuppression in the immediate post-operative period. Surgery induced immunosuppression has been implicated in the development of post-operative septic complications and tumour metastasis formation. In addition the effectiveness of many treatments in the adjuvant setting is dependent on a functioning immune system. By understanding the mechanisms contributing to surgery-induced immunosuppression, surgeons may undertake strategies to minimise its effect and reduce potential short-term and long-term consequences to patients.

Interactive comorbidity between opioid drug abuse and HIV-1 Tat: chronic exposure augments spine loss and sublethal dendritic pathology in striatal neurons

HIV-1 infection predisposes the central nervous system to damage by opportunistic infections and environmental insults. Such maladaptive plasticity may underlie the exaggerated comorbidity seen with HIV-1 infection and opioid abuse. Although morphine and HIV-1 Tat synergize at high concentrations to increase neuronal death in vitro, we questioned whether chronic low Tat exposure in vivo might contribute to the spectrum of neuropathology through sublethal neuronal injury. We used a doxycycline-driven, inducible, HIV-1 Tat transgenic mouse, in which striatal neuron death was previously shown to be absent, to examine effects of differential Tat expression, alone and combined with morphine. Low constitutive Tat expression caused neurodegeneration; higher levels induced by 7 days of doxycycline significantly reduced dendritic spine numbers. Moreover, Tat expression widely disrupted the endogenous opioid system, altering mu and kappa, but not delta, opioid receptor and proopiomelanocortin, proenkephalin, and prodynorphin transcript levels in cortex, hippocampus, and striatum. In addition to markedly reducing spine density by itself, morphine amplified the effect of higher levels of Tat on spines, and also potentiated Tat-mediated dendritic pathology, thus contributing to maladaptive neuroplasticity at multiple levels. The dendritic pathology and reductions in spine density suggest that sustained Tat +/- morphine exposure underlie key aspects of chronic neurodegenerative changes in neuroAIDS, which may contribute to the exacerbated neurological impairment in HIV patients who abuse opioids.

Morphine-sparing effect by COX-1 inhibitor sustains analgesic function without compromising antigen-specific immunity and antitumor effect of naked DNA vaccine

Morphine and ketorolac, two analgesics with different mechanisms, have been widely used in controlling cancer pain and postoperative pain in surgery. Our previous study revealed that morphine could suppress the anti-tumor effect of antigen-specific DNA vaccine. In this study, we further evaluated and compared another analgesic drug, ketorolac, with morphine for its analgesic functions and the antitumor immunities of antigen-specific DNA vaccine. We first observed that ketorolac-treated mice did not enhance tumorigenesis nor suppress the anti-tumor effects of antigen-specific (calreticulin linked to HPV16 E7) CRT/E7 DNA vaccine. We then demonstrated that ketorolac was less potent in inducing apoptosis of T lymphocytes and the generation of reactive oxygen species, in reducing mitochondrial membrane potentials, and leading to the activation of caspases 3 and 7 in T lymphocytes than morphine. When CRT/E7 DNA vaccinated mice treated with ketorolac, the declines of frequencies of E7-specific IFN-gamma-secreting CD8+ T cell precursors were slower in the morphine-treated group. CRT/E7 DNA vaccinated mice, treated with a mixture of morphine and ketorolac, could maintain the analgesic function without experiencing a decrease in the anti-tumor effects. CRT/E7 DNA vaccine with the opioid-sparing effect of ketorolac could provide potent anti-tumor effects and good analgesic function.

Serine proteases and protease-activated receptor 2-dependent allodynia: a novel cancer pain pathway

Mediators involved in the generation of pain in patients with cancer are poorly understood. Using a combined molecular, pharmacologic, behavioral, and genetic approach, we have identified a novel mechanism of cancer-dependent allodynia induced by protease-activated receptor 2 (PAR2). Here we show that human head and neck carcinoma cells have increased levels of proteolytic activity compared to normal human cell controls. Supernatant from human carcinoma cells, but not controls, caused marked and prolonged mechanical allodynia in mice, when administered into the hindpaw. This nociceptive effect was abolished by serine protease inhibition, diminished by mast cell depletion and absent in PAR2-deficient mice. In addition, non-contact co-culture of trigeminal ganglion neurons with human head and neck carcinoma cells increased the proportion of neurons that exhibited PAR2-immunoreactivity. Our results point to a direct role for serine proteases and their receptor in the pathogenesis of cancer pain. This previously unrecognized cancer pain pathway has important therapeutic implications wherein serine protease inhibitors and PAR2 antagonists may be useful for the treatment of cancer pain.

Nociceptin/orphanin FQ suppresses adaptive immune responses in vivo and at picomolar levels in vitro

Nociceptin/orphanin FQ (N/OFQ), added in vitro to murine spleen cells in the picomolar range, suppressed antibody formation to sheep red blood cells in a primary and a secondary plaque-forming cell assay. The activity of the peptide was maximal at 10(-12) M, with an asymmetric U-shaped dose-response curve that extended activity to 10(-14) M. Suppression was not blocked by pretreatment with naloxone. Specificity of the suppressive response was shown using affinity-purified rabbit antibodies against two N/OFQ peptides and with a pharmacological antagonist. Antisera against both peptides were active, in a dose-related manner, in neutralizing N/OFQ-mediated immunosuppression, when the peptide was used at concentrations from 10(-12.3) to 10(-11.6) M. In addition, nociceptin given in vivo by osmotic pump for 48 h suppressed the capacity of spleen cells placed ex vivo to make an anti-sheep red blood cell response. These studies show that nociceptin directly inhibits an adaptive immune response, i.e., antibody formation, both in vitro and in vivo.

Trigeminal injury causes kappa opioid-dependent allodynic, glial and immune cell responses in mice

BACKGROUND

The dynorphin-kappa opioid receptor (KOR) system regulates glial proliferation after sciatic nerve injury. Here, we investigated its role in cell proliferation following partial ligation of infraorbital nerve (pIONL), a model for trigeminal neuropathic pain. Mechanical allodynia was enhanced in KOR gene deleted mice (KOR-/-) compared to wild type mice. Using bromodeoxyuridine (BrdU) as a mitotic marker, we assessed cell proliferation in three different areas of the trigeminal afferent pathway: trigeminal nucleus principalis (Vp), trigeminal root entry zone (TREZ), and trigeminal ganglion (TG).

RESULTS

In KOR-/- mice or norBNI-treated mice, the number of proliferating cells in the Vp was significantly less than in WT mice, whereas cell proliferation was enhanced in TREZ and TG. The majority of the proliferating cells were nestin positive stem cells or CD11b positive microglia in the Vp and macrophages in the TG. GFAP-positive astrocytes made a clear borderline between the CNS and the PNS in TREZ, and phosphorylated KOR staining (KOR-p) was detectable only in the astrocytes in CNS in WT mice but not in KOR-/- or norBNI-treated mice.

CONCLUSIONS

These results show that kappa opioid receptor system has different effects after pIONL in CNS and PNS: KOR activation promotes CNS astrocytosis and microglial or stem cell proliferation but inhibits macrophage proliferation in PNS. The trigeminal central root has a key role in the etiology and treatment of trigeminal neuralgia, and these newly identified responses may provide new targets for developing pain therapies.

Morphine and rapid disease progression in nonhuman primate model of AIDS: inverse correlation between disease progression and virus evolution

HIV and simian immunodeficiency virus (SIV) have a formidable capacity for mutation and adaptation, a characteristic that has contributed to the extensive genetic variability. Evolutionary pressures imposed within the host and the viral capacity to mutate lead to the generation of such variants. To date, very little information is available regarding the evolution of HIV with drug abuse as a cofounding factor. Using our macaque model of drug dependency and AIDS, we have investigated the dynamics of SIV mutations in the genes tat, vpr, envelope, and nef. The results presented in this review, from our laboratory and others, contribute to the overall understanding of how drugs of abuse might influence immune selective pressure contribution to variation in different SIV genes. Additionally, the studies presented could help enlighten the development of HIV vaccines that take into consideration viral diversity.

The mysterious case of spontaneous disappearance of hepatocellular carcinoma

We describe the case of a 77-year-old woman with chronic hepatitis C and well compensated cirrhosis in whom a single encapsulated 5.5 cm hepatocellular carcinoma was found in the right liver lobe. The patient was symptomatic with left upper quadrant pain and had elevated alfa-fetoprotein levels (3133 ng/ml). While she was waiting for liver resection and 2 months after the initial diagnosis the pain improved and alfa-fetoprotein levels normalized. A computerized tomography scan showed reduction in size of the lesion to 2.5 cm, with no central arterial enhancement, but with the demonstration of a peripheral rim enhancing in all dynamic phases. Follow up computerized tomography and magnetic resonance imaging examinations showed further reduction in size of the lesion to 1.3 cm with persistence of the enhancing rim 20 months after the initial diagnosis. The spontaneous and durable regression of the HCC and the persistent peripheral enhancing rim could be explained by a strong and persistent activation of the immune system directed against the neoplastic cells.

Methionine-enkephalin secreted by human colorectal cancer cells suppresses T lymphocytes

The role of methionine-enkephalin (MENK) as an immunomodulator in colorectal carcinomas (CRC) was examined. MENK was produced in CT26, IEC6A, Colo320, and HT29 CRC cell lines but not in IEC6 intestinal cells. MENK secretion was associated with tumorigenicity and metastasis of CRC cells in syngeneic rodent models. The MENK concentration in subcutaneous tumors of CT26 and IEC6A CRC cells exhibited an inverse correlation with the number of tumor-infiltrating T lymphocytes. MENK inhibited the growth of MOLT-4 T-lymphoblastic cells in a dose-dependent manner. Furthermore, it increased the phosphorylation level of c-Jun N-terminal kinase and induced apoptosis in MOLT-4 cells. MENK-induced apoptosis was abrogated by a c-Jun N-terminal kinase inhibitor. Immunohistochemical analysis revealed moderate to strong expression of MENK in 33 (54%) of 61 CRC. MENK expression was associated with Dukes' staging, nodal metastasis, and liver metastasis. The MENK concentration in tumor tissues was higher in Dukes' C cases than in Dukes' B cases. MENK expression was associated with tumor-infiltrating T lymphocytes, especially those belonging to the CD4(+) subset. These findings suggest that MENK secreted by CRC cells caused escape of the host from the effects of immunity.

The MOR-1 opioid receptor regulates glucose homeostasis by modulating insulin secretion

In addition to producing analgesia, opioids have also been proposed to regulate glucose homeostasis by altering insulin secretion. A considerable controversy exists, however, regarding the contribution of the mu-opioid receptor (MOR-1) to insulin secretion dynamics. We employed congenic C57BL/6J MOR-1 knockout (KO) mice to clarify the role of MOR in glucose homeostasis. We first found that both sexes of MOR-1 KO mice weigh more than wild-type mice throughout postnatal life and that this increase includes preferentially increased fat deposition. We also found that MOR-1 KO mice exhibit enhanced glucose tolerance that results from insulin hypersecretion that reflects increased beta-cell mass and increased secretory dynamics in the MOR-1 mutant mice compared with wild type. Analysis of the isolated islets indicated that islet insulin hypersecretion is mediated directly by MOR expressed on islet cells via a mechanism downstream of ATP-sensitive K(+) channel activation by glucose. These findings indicate that MOR-1 regulates body weight by a mechanism that involves insulin secretion and thus may represent a novel target for new diabetes therapies.

Cloning of opioid receptors in common carp (Cyprinus carpio L.) and their involvement in regulation of stress and immune response

In mammals opiate alkaloids and endogenous opioid peptides exert their physiological and pharmacological actions through opioid receptors (MOR, DOR and KOR) expressed not only on neuroendocrine cells but also on leukocytes. Therefore, opioids can modulate the immune response. We cloned and sequenced all three classical opioid receptors (MOR, DOR and KOR) in common carp, and studied changes in their expression during stress and immune responses. Messenger RNA of opioid receptors was constitutively expressed in brain areas, specially in the preoptic nucleus NPO (homologous to mammalian hypothalamus). After exposure to prolonged restraint stress, mRNA levels of MOR and DOR decreased in the NPO and in the head kidney. Increased expression of all studied opioid receptors was observed in the pituitary pars distalis (containing ACTH-producing cells). In immune organs, constitutive but lower expression of opioid receptor genes was observed. During in vivo zymosan-induced peritonitis or after in vitro LPS-induced stimulation, when pro-inflammatory functions are activated, expression of the OR genes in leukocytes was concomitantly up-regulated. Additionally, specific agonists of opioid receptors especially reduced leukocyte migratory properties, manifested by reduced chemotaxis and down-regulated expression of chemokine receptors. Our data indicate an evolutionary conserved role for the opioid system in maintaining a dynamic equilibrium while coping with stress and/or infection.

Morphine affects the inflammatory response in carp by impairment of leukocyte migration

Opioid peptides are evolutionary conserved and in teleost fish their specific receptor types have been identified not only on neuroendocrine cells but also on immunocytes. In the present work we have studied the effects of morphine, ligand for the mu3 opioid receptor, on innate immune responses of common carp. Both in vitro and in vivo, during zymosan-induced peritonitis, morphine reduced gene expression of pro-inflammatory cytokines/chemokines and chemokine receptors. Furthermore, in vitro morphine administration also affects nitric oxide production, chemotaxis and apoptosis of head kidney leukocytes. These results provide evidence for an anti-inflammatory function of morphine and suggest an evolutionary conserved cross-talk between chemokines and opioids.

CCL5/RANTES gene deletion attenuates opioid-induced increases in glial CCL2/MCP-1 immunoreactivity and activation in HIV-1 Tat-exposed mice

To assess the role of CC-chemokine ligand 5 (CCL5)/RANTES in opiate drug abuse and human immunodeficiency virus type 1 (HIV-1) comorbidity, the effects of systemic morphine and intrastriatal HIV-1 Tat on macrophage/microglial and astroglial activation were assessed in wild-type and CCL5 knockout mice. Mice were injected intrastriatally with vehicle or Tat and assessed after 7 days. Morphine was administered to some Tat-injected mice via time-release implant (5 mg/day, s.c. for 5 days) starting at 2 days post injection. Glial activation was significantly reduced in CCL5(-/-) compared to wild-type mice at 7 days following combined Tat and morphine exposure. Moreover, the percentage of 3-nitrotyrosine immunopositive macrophages/microglia was markedly reduced in CCL5(-/-) mice injected with Tat +/- morphine compared to wild-type counterparts, suggesting that CCL5 contributes to nitrosative stress in HIV-1 encephalitis. In CCL5(-/-) mice, the reductions in Tat +/- morphine-induced gliosis coincided with significant declines in the proportion of CCL2/MCP-1-immunoreactive astrocytes and macrophages/microglia compared to wild-type counterparts. In knockout mice, neither Tat alone nor in combination with morphine increased the proportion of CCL2-immunoreactive astrocytes above percentages seen in vehicle-injected controls. Macrophages/microglia differed showing modest, albeit significant, increases in the proportion of CCL2-positive cells with combined Tat and morphine exposure, suggesting that CCL5 preferentially affects CCL2 expression by astroglia. Thus, CCL5 mediates glial activation caused by Tat and morphine, thereby aggravating HIV-1 neuropathogenesis in opiate abusers and non-abusers. CCL5 is implicated as mediating the cytokine-driven amplification of CCL2 production by astrocytes and resultant macrophage/microglial recruitment and activation.

Anesthetics, immune cells, and immune responses

General anesthesia accompanied by surgical stress is considered to suppress immunity, presumably by directly affecting the immune system or activating the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. Along with stress such as surgery, blood transfusion, hypothermia, hyperglycemia, and postoperative pain, anesthetics per se are associated with suppressed immunity during perioperative periods because every anesthetic has direct suppressive effects on cellular and neurohumoral immunity through influencing the functions of immunocompetent cells and inflammatory mediator gene expression and secretion. Particularly in cancer patients, immunosuppression attributable to anesthetics, such as the dysfunction of natural killer cells and lymphocytes, may accelerate the growth and metastases of residual malignant cells, thereby worsening prognoses. Alternatively, the anti-inflammatory effects of anesthetics may be beneficial in distinct situations involving ischemia and reperfusion injury or the systemic inflammatory response syndrome (SIRS). Clinical anesthesiologists should select anesthetics and choose anesthetic methods with careful consideration of the clinical situation and the immune status of critically ill patients, in regard to long-term mortality, morbidity, and the optimal prognosis.

Morphine suppresses intracellular interferon-alpha expression in neuronal cells

Interferon alpha (IFN-alpha) not only plays a key role in innate host immunity against infections but also is involved in the cellular functions of the central nervous system (CNS). In this study, we examined the impact of morphine on IFN-alpha expression in human neuronal cells (NT2-N). Similar to human immune cells, NT2-N cells also expressed IFN-alpha at both mRNA and protein levels. IFN-alpha expression in NT2-N cells, however, was inhibited by morphine. Naltrexone antagonized the inhibitory effect of morphine on IFN-alpha expression in NT2-N cells. The specific mu opioid receptor antagonist, Cys2, Tyr3, Arg5, Pen7-amide (CTAP), also blocked the morphine action on intracellular IFN-alpha expression. Investigation of the mechanisms involved in the morphine action showed that although morphine had little effect on the expression of key IFN regulatory factors (IRFs), morphine inhibited IFN-alpha promoter activation and suppressed the expression and phosphorylation of signal transducer and activator of transcription 1 (STAT1) in the neuronal cells. These findings provide direct in vitro evidence that opioids may impair neuronal cell-mediated innate protection in the CNS.

Alvimopan and COX-2 inhibition reverse opioid and inflammatory components of postoperative ileus

Our objective was to investigate the therapeutic potential of peripheral opioid antagonism with alvimopan and anti-inflammatory cyclooxygenase 2 (COX-2) inhibition in an animal model of postoperative ileus with pain management. Intestinal manipulation was conducted in mice and rats with or without postoperative morphine injection. Rodents were orally fed non-digestible fluorescein (FITC)-labelled dextran and transit measured after a period of 90 min. The immunomodulatory effects of morphine and alvimopan were determined on nitric oxide released from the organ cultured muscularis externa. Surgical manipulation of the intestine resulted in a delay in gastrointestinal transit after 24 h that worsened with exogenous morphine. Alvimopan did not significantly alter transit of control or manipulated animals, but significantly antagonized the transit delaying effects of morphine. However, when the inflammatory component was robust enough to obscure a further opioid induced delay in gastrointestinal transit, alvimopan ceased to be effective in improving postoperative intestinal function. Cyclooxygenase 2 inhibition significantly diminished the inflammatory component of postoperative ileus. Surgical manipulation resulted in an increased release of nitric oxide from the inflamed isolated muscularis externa in 24-h organ culture which was not altered by morphine or alvimopan. Two distinct mechanisms exist which participate in postoperative bowel dysfunction: a local inflammatory response which is antagonized by COX-2 inhibition, and a morphine-induced alteration in neural function which can be blocked with alvimopan.

Buprenorphine and methadone maintenance treatment of heroin addicts preserves immune function

Opiate addiction influences many physiological functions including immune responses. The objective of this study was to investigate the immune system function in heroin addicted patients submitted to methadone or buprenorphine maintenance treatment compared to untreated heroin addicts and healthy controls. Four groups were studied: group A included nine heroin addicted subjects, who were still injecting heroin; groups B and C were composed of 12 patients previously addicted to heroin, being treated with methadone (mean dosage 58+/-12.7 mg/day) or buprenorphine (mean dose 9.3+/-2.3mg/day) since at least 6 months; group D was composed of 15 sex and age matched healthy controls. Lymphoproliferation and peripheral mononuclear cell cultures production of the Th1 cytokines IL-2 and IFN-gamma, the Th2 cytokine IL-4, and of the pro-inflammatory cytokine TNF-alpha were evaluated in all the patients and controls. PHA-lymphoproliferation was lower in untreated heroin addicts than in controls, while it was normal in methadone and buprenorphine treated patients. An altered Th1/Th2 balance, characterized by reduced IL-4, IFN-gamma and TNF-alpha but normal IL-2 levels, was present in untreated heroin addicted subjects, while the Th1/Th2 balance was well conserved in the methadone and buprenorphine groups. These findings suggest that the immune system abnormalities in heroin addicted patients can be restored to almost normal values by controlled treatment with methadone and buprenorphine.

Non-peptidic delta-opioid receptor antagonists suppress mitogen-induced tryptophan degradation in peripheral blood mononuclear cells in vitro

Opioid receptors are expressed not only on neuroendocrine cells but also on immunocompetent cells such as lymphocytes, monocytes and macrophages. micro-Opioid receptor agonists were found to exert immunosuppressive effects, whereas delta-opioid receptor agonists have been shown to act as immunostimulants. delta-Opioid receptor agonists stimulate T and B cells and activate granulocytes and monocytes, conversely, immunostimulation can be blocked by the non-peptidic delta-opioid receptor antagonist (NTI). We investigated the impact of NTI and of the two structurally related compounds HS-378 and HS-459 on degradation of tryptophan and formation of neopterin in mitogen-stimulated human peripheral blood mononuclear cells (PBMC). Both these biochemical pathways were found to be suppressed by all three opioid receptor antagonists, HS-378 and HS-459 exhibiting slightly greater potency than NTI. The suppression of tryptophan degradation suggests that the tested delta-opioid antagonists are able to influence the serotonergic system via a non-opioid action.

Cocaine-mediated enhancement of virus replication in macrophages: implications for human immunodeficiency virus-associated dementia

Injection drug use has been recognized as a major risk factor for acquired immunodeficiency syndrome (AIDS) from the outset of the epidemic. Cocaine, one of the most widely abused drugs in the United States, can both impair the functions of macrophages and CD4(+) lymphocytes and also activate human immunodeficiency virus (HIV)-1 expression in these cells. Because the brain is the target organ for both cocaine and HIV, the objective of the present study was to explore the effects of cocaine on virus replication in macrophages, the target cells for the virus in the central nervous system (CNS). Cocaine markedly enhanced virus production in simian human immunodeficiency virus (SHIV)-infected monocyte-derived macrophages (MDMs) and in U1 cells, a chronically infected promonocytic cell line as monitored by enzyme-linked immunosorbent assay (ELISA) and immunocytochemistry. Cocaine treatment also resulted in the activation of nuclear factor (NF)-kappa B and transcriptional activation of the HIV-LTR (long terminal repeat) gag-GFP (green fluorescent protein). Analyses of chemokines in cocaine-treated macrophages by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and Luminex assays suggested increased expression of interleukin (IL)-10, a cytokine that is known to promote HIV replication in MDMs. In addition to enhancing IL-10 expression, cocaine also caused an up-regulation of the macrophage activation marker, human leukocyte antigen (HLA)-DR, in MDMs. The synergistic effect of cocaine on virus replication and its enhancement of host activation markers suggest that cocaine functions at multiple pathways to accelerate HIV-associated dementia (HAD).

Deletion of mu-opioid receptor in mice alters the development of acute neuroinflammation

The realization that the mu-opioid system plays a key role in the control of the process of neuroinflammation is a new concept that may lead to identification of novel therapies for this extremely widespread and intractable syndrome. Fever is the hallmark among the defense mechanisms evoked by the entry into the body of pathogens to initiate the innate immune responses. In an attempt to determine the possible involvement of mu-opioid receptors in the control of brain inflammation, we examined the effect of their deletion on the fever induced by i.c.v. injection of lipopolysaccharide (LPS). The first series of experiments examined the thermal consequence of the absence of mu-opioid receptors on circadian body temperature rhythm and basal body temperature. Mu-opioid receptor knockout mice (MOP-KO) showed a normal circadian body temperature rhythm and basal body temperature compared with the wild type (WT). The second series of experiments investigated i.c.v. administration of LPS on body temperature in WT and MOP-KO. In the WT, i.c.v. injection of 100 ng of LPS induced fever, but there was no increase in body temperature in the MOP-KO mice. Saline, given i.c.v., did not alter the body temperature, either in WT or MOP-KO. These results show that the mu-opioid system participates in the control of acute neuroinflammation, further reinforcing our earlier finding that the opioid system is involved in the pathogenesis of fever induced by bacterial LPS, and that mu-opioid receptors are the target for morphine-induced hyperthermia.

Intrathecal morphine suppresses immune function in rats with inflammatory-induced pain

Acute and chronic systemic administration of morphine is known to suppress immune function; however, the effect of chronic intrathecal (IT) morphine on immune function in inflammatory-induced pain is still unclear. This study examined the effects on the immune system of IT morphine in rats with formalin-induced pain. Lumbar IT catheters were implanted in rats and saline or 2.5, 5.0 or 10.0 microg/h morphine were administered for 7 days. On the last day, formalin-induced inflammatory pain was induced in rat hind paws and pain intensity was assessed. Rat spleens were then harvested for immune function assay. The IT morphine induced a dose-dependent analgesic effect and lactic acid dehydrogenase release assay showed dose-dependent suppression of natural killer cell activity. Concanavalin-A-induced splenocyte proliferation assay showed IT morphine to suppress T lymphocyte function in a dose-dependent manner. Flow cytometry showed IT morphine significantly to decrease T lymphocyte function and the percentages of T lymphocyte subsets in a dose-dependent manner. Hence, in inflammatory-induced pain IT morphine was found to suppress immune function. Chronic IT morphine should be used cautiously to treat chronic pain in immunocompromised cases.

Buprenorphine ameliorates the effect of surgery on hypothalamus-pituitary-adrenal axis, natural killer cell activity and metastatic colonization in rats in comparison with morphine or fentanyl treatment

Not all opioids employed in clinical practice share the same immunosuppressive properties. The potent partial micro-agonist buprenorphine appears to exhibit a neutral effect on the immune responses. Surgery stress is associated with decreased natural killer cell activity (NK) and enhancement of tumor metastasis in rats. We analyzed the ability of buprenorphine to prevent the effects of experimental surgery on HPA activation (plasma corticosterone levels), NK activity and lung diffusion of the NK sensitive tumor MADB106. Buprenorphine (0.1mg/kg) was compared with equianalgesic doses of fentanyl (0.1mg/kg) and morphine (10mg/kg) in this animal model. In normal animals morphine and fentanyl stimulate the HPA axis, decrease NK activity and augment tumor metastasis, while buprenorphine is devoid of these effects. Surgery significantly raised corticosterone levels, suppressed NK activity and increased MADB106 metastasis. Only buprenorphine was able to prevent the neuroendocrine and immune system alterations and ameliorate the increase of tumor metastasis induced by surgical stress. These preclinical findings suggest that an adequate treatment of surgically induced stress immunosuppression with an opioid drug devoid of immunosuppressive effects may also play a protective role against the metastatic diffusion following cancer surgery.

Opioid receptor blockade increases the number of lymphocytes without altering T cell response in draining lymph nodes in vivo

A number of studies have been dedicated to estimate the consequences on immunity of the clinical use of opioids by focusing on mitogen-induced polyclonal proliferation of T cells from blood or spleen. Here we examined, under physiological conditions, the contribution of endogenous opioids in the development of a CD4(+) T cell response within draining lymph nodes. We show in OVA-primed DO11.10 mice that delta-opioid receptors were up-regulated upon T cell activation in vivo and that opioid receptor neutralization increased the number of specific anti-OVA T lymphocytes without promoting their capacity to proliferate. The sensitivity to Fas-mediated apoptosis of T lymphocytes and the synthesis of homeostatic lymphoid chemokines were not either affected suggesting that opioids operate mainly before the entry of T lymphocytes into lymph nodes.

Influence of pain treatment by epidural fentanyl and bupivacaine on homing of opioid-containing leukocytes to surgical wounds

Endogenous opioids released from leukocytes extravasating into injured tissue can interact with peripheral opioid receptors to inhibit nociception. Animal studies have shown that the homing of opioid-producing leukocytes to the injured site is modulated by spinal blockade of noxious input. This study investigated whether epidural analgesia (EDA) influences the migration of beta-endorphin (END) and/or met-enkephalin (ENK)-containing leukocytes into the subcutaneous wound tissue of patients undergoing abdominal surgery. In part I patients received general anesthesia combined either with intra- and postoperative EDA (with bupivacaine and fentanyl) or with postoperative patient controlled intravenous analgesia (PCIA; with the opioid piritramide). In part II patients received general anesthesia combined with either epidural fentanyl or bupivacaine which was continued postoperatively. Samples of cutanous and subcutanous tissue were taken from the wound site at the beginning, at the end and at various times after surgery, and were examined by immunohistochemistry for the presence of END and ENK. We found that (i) epidural bupivacaine, fentanyl and PCIA provided similar and clinically acceptable postoperative pain relief; (ii) compared to PCIA, epidural bupivacaine or fentanyl did not change the gross inflammatory reaction within the surgical wound; (iii) opioid-containing leukocytes were almost absent in normal subcutaneous tissue but migrated to the inflamed wound tissue in ascending numbers within a few hours, reaching a peak at about 24 h after surgery; (iv) compared to PCIA, EDA resulted in significantly decreased homing of END-containing leukocytes to the injured site at 24 h after surgery; and (v) the magnitude of this decrease was similar regardless of the epidural medication. These findings suggest that nociceptive but not sympathetic neurons are primarily involved in the attraction of opioid-containing leukocytes during early stages of inflammation.

Autoradiographic analysis of GABAA receptors in mu-opioid receptor knockout mice

Anatomical evidence indicates that gamma-aminobutyric acid (GABA)-ergic and opioidergic systems are closely linked and act on the same neurons. However, the regulatory mechanisms between GABAergic and opioidergic system have not been well characterized. In the present study, we investigated whether there are changes in GABA(A) receptors in mice lacking mu-opioid receptor gene. The GABA(A) receptor binding was carried out by autoradiography using [(3)H]-muscimol (GABA(A)), [(3)H]-flunitrazepam (FNZ, native type 1 benzodiazepine) and [(35)S]-t-butylbicyclophosphorothionate (TBPS, binding to GABA(A)-gated chloride channels) in brain slices of wild type and mu-opioid receptor knockout mice. The binding of [(3)H]-FNZ in mu-opioid receptor knockout mice was significantly higher than that of the wild type controls in most of the cortex and hippocampal CA1 and CA2 formations. mu-Opioid receptor knockout mice show significantly lower binding of [(35)S]-TBPS than that of the wild type mice in few of the cortical areas including ectorhinal cortex layers I, III, and V, but not in the hippocampus. There was no significant difference in binding of [(3)H]-muscimol between mu-opioid receptor knockout and wild type mice in the cortex and hippocampus. These data indicate that there are specific regional changes in GABA(A) receptor binding sites in mu-opioid receptor knockout mice. These data also suggest that there are compensatory up-regulation of benzodiazepine binding site of GABA(A) receptors in the cortex and hippocampus and down-regulation of GABA-gated chloride channel binding site of GABA(A) receptors in the cortex of the mu-opioid receptor knockout mice.

Dynorphin activates quorum sensing quinolone signaling in Pseudomonas aeruginosa

There is now substantial evidence that compounds released during host stress directly activate the virulence of certain opportunistic pathogens. Here, we considered that endogenous opioids might function as such compounds, given that they are among the first signals to be released at multiple tissue sites during host stress. We tested the ability of various opioid compounds to enhance the virulence of Pseudomonas aeruginosa using pyocyanin production as a biological readout, and demonstrated enhanced virulence when P. aeruginosa was exposed to synthetic (U-50,488) and endogenous (dynorphin) κ-agonists. Using various mutants and reporter strains of P. aeruginosa, we identified involvement of key elements of the quorum sensing circuitry such as the global transcriptional regulator MvfR and the quorum sensing-related quinolone signaling molecules PQS, HHQ, and HQNO that respond to κ-opioids. The in vivo significance of κ-opioid signaling of P. aeruginosa was demonstrated in mice by showing that dynorphin is released from the intestinal mucosa following ischemia/reperfusion injury, activates quinolone signaling in P. aeruginosa, and enhances the virulence of P. aeruginosa against Lactobacillus spp. and Caenorhabditis elegans. Taken together, these data demonstrate that P. aeruginosa can intercept opioid compounds released during host stress and integrate them into core elements of quorum sensing circuitry leading to enhanced virulence.

Precisely how bacterial pathogens such as Pseudomonas aeruginosa cause fatal infections in critically ill humans is unknown. Evidence suggests that a major source of infection may be the patient's own intestinal microflora, which is subjected to unusual environmental conditions during critical illness. Here, we show that intestinal P. aeruginosa can be alerted to the presence of a physiological disturbance in its host by dynorphin, a human morphine-like chemical released during severe stress. Exposure of P. aeruginosa to dynorphin activates its virulence machinery to produce harmful toxins and to suppress the growth of probiotic bacteria, which are known to promote intestinal health. The molecular mechanisms of these events involve the activation of highly regulated virulence machinery in Pseudomonas, called quorum sensing, that allows bacteria to sense host stress and respond with enhanced harmfulness. These observations suggest that opportunistic pathogens like P. aeruginosa are equipped with sophisticated surveillance systems that take advantage of a weakened host by intercepting and responding to naturally occurring host chemicals that are normally used as signaling molecules for immune activation and analgesia. Elucidation of the effect of dynorphin on Pseudomonas exposes a major mechanism by which this organism behaves as a true opportunist.

Morphine reciprocally regulates IL-10 and IL-12 production by monocyte-derived human dendritic cells and enhances T cell activation

We evaluated the effect of morphine on human dendritic cells (DCs). Interestingly, immature DCs were found to express all 3 (mu, kappa, delta) opioid receptors on the cell surface. Chronic morphine treatment (10(-8) to 10(-12) M) during the development of DCs from monocytes augmented LPS-induced upregulation of HLA-DR, CD86, CD80, and CD83 and increased the T cell stimulatory capacity of DCs, which could be inhibited by naloxone, an opioid receptor antagonist. The change in surface phenotype was paralleled by a p38 MAPK-dependent decrease in IL-10 and increase in IL-12 secretion. Our data indicate that morphine exerts an immunostimulatory effect by modulating LPS-induced DC maturation.

Morphine reciprocally regulates IL-10 and IL-12 production by monocyte-derived human dendritic cells and enhances T cell activation

We evaluated the effect of morphine on human dendritic cells (DCs). Interestingly, immature DCs were found to express all 3 (mu, kappa, delta) opioid receptors on the cell surface. Chronic morphine treatment (10(-8) to 10(-12) M) during the development of DCs from monocytes augmented LPS-induced upregulation of HLA-DR, CD86, CD80, and CD83 and increased the T cell stimulatory capacity of DCs, which could be inhibited by naloxone, an opioid receptor antagonist. The change in surface phenotype was paralleled by a p38 MAPK-dependent decrease in IL-10 and increase in IL-12 secretion. Our data indicate that morphine exerts an immunostimulatory effect by modulating LPS-induced DC maturation.