Opiate receptors on lymphocytes and platelets in man

HIV-1 and opiates modulate miRNA profiles in extracellular vesicles

Opiate abuse increases the risk of HIV transmission and exacerbates HIV neuropathology by increasing inflammation and modulating immune cell function. Exosomal EVs(xEV) contain miRNAs that may be differentially expressed due to HIV infection or opiate abuse. Here we develop a preliminary exosomal-miRNA biomarker profile of HIV-infected PBMCs in the context of opiate use. PBMCs infected with HIV were treated with increasing dosages of morphine for 72 hours, the culture supernatants were collected, and the exosomes isolated using differential centrifugation. Exosomal miRNAs were extracted, expression levels determined via Nanostring multiplexed microRNA arrays, and analyzed with Webgestalt. The effect of the exosomes on neuronal function was determined by measuring calcium. Preliminary findings show that HIV-1 infection altered the miRNA profile of PBMC-derived EVs concurrently with opiate exposure. MicroRNA, hsa-miR-1246 was up-regulated 12-fold in the presence of morphine, relative to uninfected control. PBMCs infected with HIV-1 MN, an X4-tropic HIV-1 strain and exposed to morphine, displayed a trend which suggests potential synergistic effects between HIV-1 infection and morphine exposure promoting an increase in viral replication. Dose-dependent differences were observed in miRNA expression as a result of opiate exposure. The xEVs derived from PBMCs exposed to morphine or HIV modulated neuronal cell function. SH-SY5Y cells, treated with xEVs derived from ART-treated PBMCs, exhibited increased viability while for SH-SY5Ys exposed to xEVs derived from HIV-1 infected PBMCs viability was decreased compared to the untreated control. Exposing SH-SY5Y to xEVs derived from HIV-infected PBMCs resulted in significant decrease in calcium signaling, relative to treatment with xEVs derived from uninfected PBMCs. Overall, HIV-1 and morphine induced differential miRNA expression in PBMC-derived exosomes, potentially identifying mechanisms of action or novel therapeutic targets involved in opiate use disorder, HIV neuropathology, TNF signaling pathway, NF-κB signaling pathway, autophagy, and apoptosis in context of HIV infection.

Interactions of fentanyl with blood platelets and plasma proteins: platelet sensitivity to prasugrel metabolite is not affected by fentanyl under in vitro conditions

BACKGROUND

Clinical trials indicate that fentanyl, like morphine, may impair intestinal absorption and thus decrease the efficacy of oral P2Y₁₂ inhibitors, such as clopidogrel, ticagrelor, and prasugrel. However, the ability of fentanyl to directly negate or reduce the inhibitory effect of P2Y₁₂ receptor antagonists on platelet function has not been established. A series of in vitro experiments was performed to investigate the ability of fentanyl to activate platelets, potentiate platelet response to ADP, and/or diminish platelet sensitivity to prasugrel metabolite (R-138727) in agonist-stimulated platelets. The selectivity and specificity of fentanyl toward major carrier proteins has been also studied.

METHODS

Blood was obtained from healthy volunteers (19 women and 12 men; mean age 40 ± 13 years). Platelet function was measured in whole blood, platelet-rich plasma and in suspensions of isolated platelets by flow cytometry, impedance and optical aggregometry. Surface plasmon resonance and molecular docking were employed to determine the binding kinetics of fentanyl to human albumin, α₁-acid glycoprotein, apolipoprotein A-1 and apolipoprotein B-100.

RESULTS

When applied at therapeutic and supratherapeutic concentrations under various experimental conditions, fentanyl had no potential to stimulate platelet activation and aggregation, or potentiate platelet response to ADP, nor did it affect platelet susceptibility to prasugrel metabolite in ADP-stimulated platelets. In addition, fentanyl was found to interact with all the examined carrier proteins with dissociation constants in the order of 10^-4 to 10^-9 M.

CONCLUSIONS

It does not seem that the delayed platelet responsiveness to oral P2Y₁₂ inhibitors, such as prasugrel, in patients undergoing percutaneous coronary intervention, results from direct interactions between fentanyl and blood platelets. Apolipoproteins, similarly to albumin and α₁-acid glycoprotein, appear to be important carriers of fentanyl in blood.

Opioid Use, Gut Dysbiosis, Inflammation, and the Nervous System

Opioid use disorder (OUD) is defined as the chronic use or misuse of prescribed or illicitly obtained opioids and is characterized by clinically significant impairment. The etiology of OUD is multifactorial as it is influenced by genetics, environmental factors, stress response and behavior. Given the profound role of the gut microbiome in health and disease states, in recent years there has been a growing interest to explore interactions between the gut microbiome and the central nervous system as a causal link and potential therapeutic source for OUD. This review describes the role of the gut microbiome and opioid-induced immunopathological disturbances at the gut epithelial surface, which collectively contribute to OUD and perpetuate the vicious cycle of addiction and relapse.

Characterization of the Presence and Function of Platelet Opioid Receptors

Opioids are typically used for the treatment of pain related to disease or surgery. In the body, they enter the bloodstream and interact with a variety of immune and neurological cells that express the μ-, δ-, and κ-opioid receptors. One blood-borne cell-like body that is not well understood in the context of opioid interactions is the platelet. The platelet is a highly sensitive anucleate cell-like fragment responsible for maintaining hemostasis through shape change and the secretion of chemical messengers. This research characterizes platelet opioid receptors, how specific receptor agonists impact platelet exocytosis, and the role of the κ-and μ-receptors in platelet function. Platelets were found to express all three opioid receptors, but upon stimulation with their respective agonist no activation was detected. Furthermore, exposure to the opioid agonists did not impact traditional platelet secretion stimulated by thrombin, a natural platelet activator. In addition, data collected from knockout mice suggest that the opioid agonists may be interacting nonspecifically with platelets. Dark-field images revealed differences in activated platelet shape between the κ- and μ-knockout platelets and the control platelets. Finally, κ-knockout platelets showed variations in their ability to adhere and aggregate compared to control platelets. Overall, these data show that platelet function is not likely to be heavily affected by blood-borne opioids.

Evaluation of complete blood cell count parameters and lymphocyte-related ratios in patients with Opioid Use Disorder

Complete blood count (CBC) parameters and lymphocyte-related ratios are found to be associated with inflammation and increased cytokine production. In Opioid Use Disorder (OUD), CBC parameters can be examined as the inflammatory (oxidative stress) biomarkers which could be used as an objective marker to support the OUD diagnosis and could be used as a disease severity marker. CBC parameters of 142 patients with OUD were examined. Lymphocytes, monocytes, basophiles, eosinophils and platelet counts (PLT), red blood cell levels (HGB), mean erythrocyte volume (MCV) and lymphocyte-related ratios were calculated. The control group consisted of 140 healthy individuals. WBC, neutrophil, lymphocyte, monocyte, platelet count, neutrophil, basophil percentage, neutrophil/ lymphocyte ratio (NLR), monocyte/lymphocyte ratio (MLR) values were significantly higher in OUD group. Lymphocyte, basophil percentage, basophile/lymphocyte ratio (BLR), red blood cell (RBC), hemoglobin were significantly higher in control group. Mean platelet volume (MPV), eosinophil/lymphocyte ratio (ELR), platelet/ lymphocyte ratio (PLR) values were not significant yet higher in the OUD group. CBC and related parameters (WBC, neutrophil, lymphocyte, monocyte, platelet count, neutrophil, basophil percentage, NLR, MLR) were found to be significantly higher in the OUD group. Evaluation of CBC parameters could be useful in treatment and follow-up of patients with OUD.

Single cell transcriptomics reveals opioid usage evokes widespread suppression of antiviral gene program

Chronic opioid usage not only causes addiction behavior through the central nervous system, but also modulates the peripheral immune system. However, how opioid impacts the immune system is still barely characterized systematically. In order to understand the immune modulatory effect of opioids in an unbiased way, here we perform single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells from opioid-dependent individuals and controls to show that chronic opioid usage evokes widespread suppression of antiviral gene program in naive monocytes, as well as in multiple immune cell types upon stimulation with the pathogen component lipopolysaccharide. Furthermore, scRNA-seq reveals the same phenomenon after a short in vitro morphine treatment. These findings indicate that both acute and chronic opioid exposure may be harmful to our immune system by suppressing the antiviral gene program. Our results suggest that further characterization of the immune modulatory effects of opioid is critical to ensure the safety of clinical opioids.

Over 100 million of opioid prescriptions are issued yearly in the USA alone, but the impact of opioid use on the immune system is barely characterized. Here the authors report antiviral immune response is blunted in several types of blood cells from opioid-dependent individuals, and when healthy donor cells are exposed to morphine in a dish.

Does pharmacotherapy influence the inflammatory responses during cardiopulmonary bypass in children?

Cardiopulmonary bypass (CPB) induces a systemic inflammatory response syndrome (SIRS) by factors such as contact of the blood with the foreign surface of the extracorporeal circuit, hypothermia, reduction of pulmonary blood flow during CPB and endotoxemia. SIRS is maintained in the postoperative phase, co-occurring with a counter anti-inflammatory response syndrome. Research on the effects of drugs administered before the surgery, especially in the induction phase of anesthesia, as well as drugs used during extracorporeal circulation, has revealed that they greatly influence these postoperative inflammatory responses. A better understanding of these processes may not only improve postoperative recovery but also enable tailor-made pharmacotherapy, with both health and economic benefits. In this review, we describe the pathophysiology of SIRS and counter anti-inflammatory response syndrome in the light of CPB in children and the influence of drugs used on these syndromes.

Behavioural, Mucosal and Systemic Immune Parameters in HIV-infected and Uninfected Injection Drug Users

OBJECTIVE

Injection drug use (IDU) remains a major risk factor for HIV-1 acquisition. The complex interplay between drug use, non-sterile injection, and Hepatitis C remains poorly understood. We conducted a pilot study to determine the effect of IDU on immune parameters among HIV-uninfected and -infected individuals. We hypothesized that IDU could further augment immunological changes associated with HIV-1 infection, which could in turn affect HIV pathogenesis.

METHODS

HIV-uninfected and -infected subjects with IDU, and non-IDU controls were recruited to obtain socio-demographic and drug-related behaviours. Blood (PBMC) and mucosal (MMC) mononuclear cells were analysed for cellular markers of immune activation (CD38 and Ki67). Serum ELISA was performed to determine levels of soluble CD14, a marker of immune activation.

RESULTS

No significant quantitative differences in CD4⁺ and CD8⁺ T cell levels were observed between IDU and non-IDU subjects when accounting for the presence of HIV-1 infection. However, increased levels of cellular and soluble markers of immune activation were documented in cells and plasma of HIV-uninfected IDU subjects compared to non-injectors. Additionally, sharing of injection paraphernalia was related to immune activation among HIV-uninfected IDU subjects.

CONCLUSION

IDU, with or without HIV-1 infection, results in a significant increase in immune activation in both the peripheral blood and the GI tract. This may have significant impact on HIV transmission, pathogenesis, and immunologic responses to combination antiviral therapy. This study provides compelling preliminary results which in turn support larger studies to better define the relationship between IDU, infection with HIV-1, co-infection with Hepatitis C and immunity.

Opioids and immune modulation: more questions than answers

Opioid addicts are more likely to present with infections suggesting opioids are immune modulators. The potential sites/mechanism(s) for this modulation are controversial and on close inspection not well supported by the current literature. It has long been assumed that opioid-induced immune modulation occurs via a combination of direct actions on the immune cell itself, via the hypothalamic-pituitary-adrenal (HPA) axis, or both. Opioid receptors are classified as MOP (μ, mu), DOP (δ, delta), and KOP (κ, kappa)--classical naloxone sensitive receptors--or NOP (the receptor for nociceptin/orphanin FQ), which is naloxone insensitive. Opioids currently used in clinical practice predominantly target the MOP receptor. There do not appear to be classical opioid receptors present on immune cells. The evidence for HPA activation is also poor and shows some species dependence. Most opioids used clinically or as drugs of abuse do not target the NOP receptor. Other possible target sites for immune modulation include the sympathetic nervous system and central sites. We are currently unable to accurately define the cellular target for immune modulation and suggest further investigation is required. Based on the differences observed when comparing studies in laboratory animals and those performed in humans we suggest that further studies in the clinical setting are needed.

Blood chromatin as a biosensor of the epigenetic milieu: a tool for studies in living psychiatric patients

This article constructs an argument for using blood chromatin (contained in nucleated blood cells) as a protein biosensor to integrate the ambient epigenetic influences in the internal milieu. An analogy is made to blood glycated hemoglobin (HbA1c) in diabetes as an integrated proxy for glucose levels and body-wide protein glycation. Genome-wide chromatin can serve as an organizing principle that bridges the central and peripheral compartments by entraining commensurable gene networks. Chromatin deposition along these networks will be imposed by the totality of epigenetic influences, which incorporates significant contributions from biochemicals that readily traverse the blood-brain barrier. In a clinical trial, these influences would be dominated by pharmaceuticals designed to override pathophysiological signals. In practice, mRNA readouts would be limited to nonsynaptic gene networks whose critical nodes are occupied by a site-specific chromatin modification. Finally, chromatin measurements in peripheral tissue will retain the influences of a patient's lifestyle and unique genomic background.

Thymoquinone-induced platelet apoptosis

Thymoquinone (TQ) is a nutrient with anticarcinogenic activity that stimulates suicidal death of tumor cells. Moreover, TQ triggers suicidal death of erythrocytes or eryptosis, an effect at least partially due to increase in cytosolic Ca(2+) activity and ceramide formation. The present experiments explored whether TQ influences apoptosis of blood platelets. Cell membrane scrambling was determined utilizing Annexin V binding to phosphatidylserine exposing platelets, cytosolic Ca(2+) activity utilizing Fluo 3-AM fluorescence, caspase activity utilizing immunofluorescence and Western blotting of active caspase-3 and inactive procaspase-3, mitochondrial potential utilizing DiOC(6) fluorescence and ceramide by FACS analysis of ceramide-binding antibodies. A 30 min exposure to TQ (≥5 µM) was followed by Annexin V binding, paralleled by caspase activation, increase of cytosolic Ca(2+) activity, mitochondrial depolarization, and ceramide formation. P-selectin exposure and integrin α(IIb) β(3) activation did not increase in response to TQ. Nominal absence of extracellular Ca(2+) blunted but did not fully abolish the TQ-induced activation of caspase-3. The effects of TQ on platelets are significantly abolished with phosphoinositide-3 kinase (PI3K) inhibitor wortmannin and G-protein coupled receptor (GPCR) inhibitor pertussis toxin treatment prior to TQ stimulation. In conclusion, TQ triggers suicidal death of blood platelets in a PI3K-dependent manner, possibly through a GPCR family receptor; an effect paralleled by increase of cytosolic Ca(2+) activity, ceramide formation, mitochondrial depolarization, and caspase-3 activation.

Methadone ameliorates multiple-low-dose streptozotocin-induced type 1 diabetes in mice

Type 1 diabetes is an autoimmune disease characterized by inflammation of pancreatic islets and destruction of beta cells by the immune system. Opioids have been shown to modulate a number of immune functions, including T helper 1 (Th1) and T helper 2 (Th2) cytokines. The immunosuppressive effect of long-term administration of opioids has been demonstrated both in animal models and humans. The aim of this study was to determine the effect of methadone, a mu-opioid receptor agonist, on type 1 diabetes. Administration of multiple low doses of streptozotocin (STZ) (MLDS) (40 mg/kg intraperitoneally for 5 consecutive days) to mice resulted in autoimmune diabetes. Mice were treated with methadone (10 mg/kg/day subcutaneously) for 24 days. Blood glucose, insulin and pancreatic cytokine levels were measured. Chronic methadone treatment significantly reduced hyperglycemia and incidence of diabetes, and restored pancreatic insulin secretion in the MLDS model. The protective effect of methadone can be overcome by pretreatment with naltrexone, an opioid receptor antagonist. Also, methadone treatment decreased the proinflammatory Th1 cytokines [interleukin (IL)-1beta, tumor necrosis factor-alpha and interferon-gamma] and increased anti-inflammatory Th2 cytokines (IL-4 and IL-10). Histopathological observations indicated that STZ-mediated destruction of beta cells was attenuated by methadone treatment. It seems that methadone as an opioid agonist may have a protective effect against destruction of beta cells and insulitis in the MLDS model of type 1 diabetes.

Human peripheral blood mononuclear cells express nociceptin/orphanin FQ, but not mu, delta, or kappa opioid receptors

BACKGROUND

Expression of opioid receptors on peripheral blood mononuclear cells (PBMC) is controversial. These receptors are currently classified as classical (MOP/mu/mu, DOP/delta/delta and KOP/kappa/kappa) and nonclassical NOP (nociceptin/orphanin FQ; N/OFQ).

METHODS

In this volunteer study we probed for the expression of both classical and nonclassical opioid receptors using 1) radioligand binding, 2) specific antibody binding, and 3) polymerase chain reaction-based experimental paradigms.

RESULTS

Membranes prepared from PBMC from healthy volunteers did not bind either [3H]diprenorphine (a nonselective radioligand for classical opioid receptors) or [3H]N/OFQ. There was significant concentration-dependent binding of each radioligand to control tissues expressing recombinant MOP and NOP. In addition, using fluorescence-activated cell sorting paradigms, there was no binding of fluorescent naloxone or either of two MOP antibodies to whole PBMC, though fluorescent naloxone did bind to recombinant MOP (as a positive control). Using primers specific for classical and nonclassical opioid receptors, and RNA extracted from the PBMC of 10 healthy volunteers, we were also unable to detect MOP, DOP, and KOP transcripts. In contrast, NOP was detected in all samples.

CONCLUSIONS

Despite using several complementary experimental strategies, we failed to demonstrate protein for classical or nonclassical opioid receptors on PBMC from healthy volunteers. We detected NOP mRNA, suggesting low-density NOP expression on these immunocytes. It is possible that N/OFQ, produced by the PBMC itself, may be involved in the control of immune function.

Topical morphine for the treatment of cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) is a potentially disfiguring parasitic disease which is endemic in many parts of the world. The evidence for optimal treatment of CL is uncongenial. The development of a compound used for the topical treatment of CL is an attractive option for overcoming the problems of toxic and expensive currently used anti-leishmanial drugs. Easy application is another attraction of topical treatment compared to systemic therapy. Evidence is certainly about a variety of immune responses in the healing process of CL. The immune modulatory effect of morphine also has been known in clinical medicine for decades. Protection against leishmaniasis is dependent upon generation of CD4(+) helper T-cells immune response. There are some evidences that opioids could be members of the cytokine family and the regulation of immune and inflammatory responses is dependent on the functions of cytokines; therefore much effort should be placed on understanding the effect of morphine on cytokine activity. Based on a previous mentioned evidence we suggest that morphine as an immunomodulator could induce the healing process of cutaneous leishmaniasis through inducing the release of a number of cytokines.

Role of G protein-gated inwardly rectifying potassium channels in P2Y12 receptor-mediated platelet functional responses

The role of the G(i)-coupled platelet P2Y(12) receptor in platelet function has been well established. However, the functional effector or effectors contributing directly to alphaIIbbeta3 activation in human platelets has not been delineated. As the P2Y(12) receptor has been shown to activate G protein-gated, inwardly rectifying potassium (GIRK) channels, we investigated whether GIRK channels mediate any of the functional responses of the platelet P2Y(12) receptor. Western blot analysis revealed that platelets express GIRK1, GIRK2, and GIRK4. In aspirin-treated and washed human platelets, 2 structurally distinct GIRK inhibitors, SCH23390 (R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride) and U50488H (trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(pyrrolidinyl)cyclohexyl] benzeneacetamide methanesulfonate), inhibited adenosine diphosphate (ADP)-, 2-methylthioADP (2-MeSADP)-, U46619-, and low-dose thrombin-mediated platelet aggregation. However, the GIRK channel inhibitors did not affect platelet aggregation induced by high concentrations of thrombin, AYPGKF, or convulxin. Furthermore, the GIRK channel inhibitors reversed SFLLRN-induced platelet aggregation, inhibited the P2Y(12)-mediated potentiation of dense granule secretion and Akt phosphorylation, and did not affect the agonist-induced G(q)-mediated platelet shape change and intracellular calcium mobilization. Unlike AR-C 69931MX, a P2Y(12) receptor-selective antagonist, the GIRK channel blockers did not affect the ADP-induced adenlylyl cyclase inhibition, indicating that they do not directly antagonize the P2Y(12) receptor. We conclude that GIRK channels are important functional effectors of the P2Y(12) receptor in human platelets.

A retrospective study of the association between haematological and biochemical parameters and morphine intolerance in patients with cancer pain

BACKGROUND

Morphine is the strong opioid of choice for the treatment of moderate to severe cancer pain according to guidelines of the World Health Organization (WHO). However, a minority of patients do not receive the desired analgesic effect or suffer intolerable side effects from morphine, and are switched to alternative opioids.

METHODS

The aim of this retrospective study was to identify factors that might be associated with morphine intolerance. Data were analysed from 100 controls who tolerated morphine and 77 patients who were switched to an alternative opioid. We investigated whether currently logged data could fully explain the need to switch. Demographic details, cancer type (histological diagnosis) and markers related to organ function were included in an analysis of biochemical and haematological parameters.

RESULTS

Patients over 78 years (P = 0.03), or with a high white cell (P = 0.002) or high platelet count (P = 0.003), were more likely to switch. Although our numbers were small, patients with severe organ impairment were more likely to switch. However, a model including white cell count, platelet count, age, serum albumin and alkaline phosphatase, accurately separated switchers and controls in only 68% of cases. There was no significant difference between the two groups in terms of the numbers of patients having cytotoxic drugs in the two weeks prior to the haematological and biochemical analysis. Similarly, there were no significant differences in histological diagnoses between groups.

CONCLUSIONS

The white cell count was the strongest single effect observed and, as such, warrants further investigation. Further studies are needed in order to accurately define a model that will predict those patients likely to be intolerant of morphine.

Morphine enhances HIV infection of neonatal macrophages

Perinatal transmission of HIV accounts for almost all new HIV infections in children. There is an increased risk of perinatal transmission of HIV with maternal illicit substance abuse. Little is known about neonatal immune system alteration and subsequent susceptibility to HIV infection after morphine exposure. We investigated the effects of morphine on HIV infection of neonatal monocyte-derived macrophages (MDM). Morphine significantly enhanced HIV infection of neonatal MDM. Morphine-induced HIV replication in neonatal MDM was completely suppressed by naltrexone, the opioid receptor antagonist. Morphine significantly up-regulated CCR5 receptor expression and inhibited the endogenous production of macrophage inflammatory protein-1beta in neonatal MDM. Thus, morphine, most likely through alteration of beta-chemokines and CCR5 receptor expression, enhances the susceptibility of neonatal MDM to HIV infection, and may have a cofactor role in perinatal HIV transmission and infection.

Morphine enhances HIV infection of human blood mononuclear phagocytes through modulation of beta-chemokines and CCR5 receptor

BACKGROUND

Injection drug use remains a significant risk for acquiring HIV infection. The mechanisms by which morphine enhances HIV infection of human immune cells are largely unknown.

OBJECTIVE

In this study, we sought to determine the possible mechanisms by which morphine upregulates HIV infection of human blood monocyte-derived macrophages (MDM).

METHODS

In this study, MDM were infected with the R5, X4, and R5X4 HIV strains. HIV replication was determined by performing reverse transcriptase activity assays. HIV receptors were determined by performing reverse transcriptase polymerase chain reactions and flow cytometry assays. beta-chemokines were analyzed by performing enzyme-linked immunosorbent assays. In addition, HIV R5 strain and murine leukemia virus envelope-pseudotyped HIV infection was performed to determine whether morphine affects HIV infection of macrophages at entry level.

RESULTS

Morphine significantly enhanced HIV R5 strain infection of MDM but had little effect on X4 strain infection. The macrophage-tropic R5 strain envelope-pseudotyped HIV infection was markedly increased by morphine, whereas murine leukemia virus envelope-pseudotyped HIV infection was not significantly affected. Furthermore, morphine significantly upregulated CCR5 receptor expression and inhibited the endogenous production of beta-chemokines in MDM. The opioid receptor antagonist naltrexone blocked the effects of morphine on the production of beta-chemokines.

CONCLUSION

Opiates enhance HIV R5 strain infection of macrophages through the downregulation of beta-chemokine production and upregulation of CCR5 receptor expression and may have an important role in HIV immunopathogenesis.

Synthetic beta-endorphin-like peptide immunorphin binds to non-opioid receptors for beta-endorphin on T lymphocytes

The synthetic decapeptide H-SLTCLVKGFY-OH (termed immunorphin) corresponding to the sequence 364-373 of the CH3 domain of human immunoglobulin G heavy chain was found to compete with [125I]beta-endorphin for high-affinity receptors on T lymphocytes from the blood of healthy donors (K(i) = 0.6 nM). Besides immunorphin, its synthetic fragments H-Val-Lys-Gly-Phe-Tyr-OH (K(i) = 15 nM), H-Leu-Val-Lys-Gly-Phe-Tyr-OH (K(i) = 8.0 nM), H-Cys-Leu-Val-Lys-Gly-Phe-Tyr-OH (K(i) = 3.4 nM), H-Thr-Cys-Leu-Val-Lys-Gly-Phe-Tyr-OH (K(i) = 2.2 nM), H-Leu-Thr-Cys-Leu-Val-Lys-Gly-Phe-Tyr-OH (K(i) = 1.0 nM) possessed the ability to inhibit specific binding of [125I]beta-endorphin to T lymphocytes. Tests of the specificity of the receptors revealed that they are not sensitive to naloxone and Met-enkephalin, i.e. they are not opioid receptors. K(d) values characterizing the specific binding of 125I- labeled immunorphin and its fragment H-Val-Lys-Gly-Phe-Tyr-OH to the receptors have been determined to be 7.4 nM and 36.3 nM, respectively.

Effects of beta-endorphin and met-enkephalin on platelet activity

In the present study, beta-endorphin and met-enkephalin were tested for their antiplatelet activity in human platelet-rich plasma (PRP). Blood samples were obtained from 15 healthy subjects. The results of the study show that these two endogenous opioids (200 pg/ml final concentration) reduce platelet aggregation when it is induced by ADP at low dose (0.5 microM). It is likely due to conformational changes on the platelet membrane that cause a non-specific decreased susceptibility to platelet-aggregating agonists.

Role of hypothalamic-pituitary axis in morphine-induced alteration in thymic cell distribution using mu-opioid receptor knockout mice

Mu-opioid receptor knockout mice (MORKO), were used to address two questions: (1) if morphine induced decrease in thymic weight and cell distribution is mediated by the mu-opioid receptor and (2) the role of corticosteroids in morphine mediated alteration in thymic cell distribution. Our result show that morphine mediated increase in plasma corticosterone is mediated by the mu-opioid receptor since morphine at doses as high as 25 mg/kg-body weight does not increase plasma corticosterone levels in the MORKO. In addition, we have also shown that morphine treatment results in the differentiation of CD4+CD8+ (double positive cells) to single positive CD4+ cells while dexamethasone treatment results in the deletion of CD4+CD8+ (double positive) cells.

Morphine-6 beta-glucuronide induces potent immunomodulation

The effect of morphine administration on immune parameters is well documented. However, there exists a limited knowledge of the effect of morphine's metabolites on immune status. The present study examines the immunomodulatory effects of the morphine metabolite, morphine-6 beta-glucuronide (M6G), in the rat and provides further evaluation of the antinociceptive effects of M6G. Animals were administered phosphate-buffered saline (PBS) or M6G in doses of 1.0, 3.16, or 10.0 mg/kg (subcutaneous (s.c.)) or 0.1, 0.316, or 1.0 microgram (intracerebroventricular (i.c.v.)). Animals were tested for antinociception in the warm water tail-withdrawal procedure. In a separate set of animals, assessments of splenic natural killer cell activity, lymphocyte proliferative responses to mitogenic stimulation, and production of interferon-gamma were made 1 h following the s.c. or i.c.v. administration of M6G. The results show that M6G induced potent antinociception that was evident for at least 120 min following administration. M6G also produced decreases in natural killer cell activity, lymphocyte proliferation, and interferon-gamma production 1 h following both routes of administration. The difference in potency between immune alterations induced by subcutaneous vs. intracerebroventricular administration suggest central mediation of the immunomodulatory properties of M6G. Thus, M6G produces significant antinociception and immunomodulation in the rat. These findings demonstrate potent immunomodulatory properties of a metabolite of morphine, 1M6G.

Involvement of substance P and central opioid receptors in morphine modulation of the CHS response

Morphine administration prior to challenge with the antigen 2,4-dinitro-fluorobenzene increases the contact hypersensitivity (CHS) response in rats. The present study extended these findings by showing that central, but not systemic, administration of N-methylnaltrexone antagonized the morphine-induced enhancement of the CHS response. The importance of the neuroimmune mediator substance P was shown via the attenuation of the morphine-induced enhancement following both systemic and topical administration of the NK-1 antagonist WIN51,708. Taken together, the findings of the present study provide new data showing that central opioid receptors and peripheral substance P are involved in the morphine-induced enhancement of the CHS response.

Opioids, opioid receptors, and the immune response

It is now clear that opioid receptors participate in the function of the cells of the immune system, and evidence suggests that opioids modulate both innate and acquired immune responses. We review literature here which establishes that mu-, kappa-, and delta-opioid compounds alter resistance to a variety of infectious agents, including the Human Immunodeficiency Virus (HIV). The nature of the immunomodulatory activity of the opioids has been the subject of a great deal of research over the last ten years. There is increasing evidence that effects of opioids on the immune response are mediated at several levels. Modulation of the inflammatory response appears to be a target of these compounds, including effects on phagocytic activity, as well as the response of cells to various chemoattractant molecules. Moreover, findings from several laboratories have demonstrated the impact of opioid treatment on antibody responses, and the molecular basis for this effect is likely due, at least in part, to the modulation of both cytokine and cytokine receptor expression. Future research should provide a clearer understanding of the cellular and molecular targets of opioid action within the immune system.

Morphine modulation of the contact hypersensitivity response: characterization of immunological changes

Previous investigations in our laboratory showed that systemic morphine administration 1 h prior to elicitation of the in vivo contact hypersensitivity (CHS) response produced a robust increase in inflammation at the site of antigen reexposure. The present study extended those findings by characterizing the effect of morphine on immunological processes important in the development of the CHS response. To induce contact hypersensitivity, the antigen 2,4-dinitrofluorobenzene was applied to the pinnae of previously sensitized rats. Morphine administration produced an increase in inducible nitric oxide synthase mRNA and the proinflammatory cytokine interleukin-6, at the site of antigen reexposure. In contrast, morphine did not alter expression of the anti-inflammatory cytokine interleukin-10. Morphine also produced an increase in the proliferation of lymphocytes from the peripheral (i.e., cervical) lymph nodes when assessed 72 h following challenge. These studies show that the morphine-induced increase in the in vivo CHS response involves immunologically specific alterations.

In vitro effects of naloxone on T-lymphocyte-dependent antibacterial activity in hepatitis C virus (HCV) infected patients and in inflammatory bowel disease (IBD) patients

Naloxone acts as an opioid antagonist, displacing opioid drugs from cellular receptors. Among opioid substances, beta-endorphins are able to bind to several cell receptors, even including those expressed by immune cells. In this respect, evidence has been provided that in the course of viral infections, as well as in patients with ulcerative colitis high levels of beta-endorphins are detectable. Here, peripheral blood lymphocytes (PBL) from 21 HCV infected patients and 14 patients with IBD, respectively, were incubated with Naloxone and Naloxone + Ca2+ in order to evaluate a putative modulation of PBL-mediated antibacterial activity. In fact, previous studies have demonstrated a reduction of this T-cell activity in HCV and IBD patients. In general terms, the above treatment led to a recovery of the depressed antibacterial activity. In some cases, increase in T lymphocyte function was obtained with Naloxone alone, while in other cases the combination Naloxone + Ca2+ gave rise to a restorative effect. Of note, in some instances, lymphocytes were unresponsive to pharmacological modulation. The overall results suggest that beta-endorphins may down modulate T-cell antibacterial response in HCV and in IBD patients by saturating peripheral receptors on immune cells. Therefore, it is likely that Naloxone and/or Naloxone + Ca2+ may displace opioid drugs, thus antagonizing their effects.

Naltrexone administration attenuates surgery-induced immune alterations in rats

Surgery is a commonly performed procedure which produces substantial alterations in immune function in both humans and animals. To better understand the mechanism of surgery-induced immunomodulation, the present study investigated the effect of the opioid antagonist naltrexone on surgery-induced immune alterations in rats. Based on previous investigations in our laboratory, rats underwent a 6-cm laparotomy with no internal manipulation and immunological assessments were completed 24 h following the surgical procedure. Naltrexone was administered at the time of surgery and every 4 h thereafter until immune assessment. Results showed that naltrexone attenuated the surgery-induced decrease in natural killer cell cytotoxicity, B-cell proliferation, T-cell proliferation, and production of the cytokine IFN-gamma. These results are among the first to show that pharmacological antagonism of opioid receptors can prevent deleterious immune changes in the postoperative state, suggesting a detrimental role of the endogenous opioids in surgical procedures.

Involvement of central mu- but not delta- or kappa-opioid receptors in immunomodulation

Studies completed in both humans and animals have shown that opioids have significant effects on the immune system via pharmacological interactions with the opioid receptor. However, the type of opioid receptor at which morphine binding produces changes in immune status has not been well characterized. To determine the type of opioid receptor involved in opioid-induced immune alterations, the present study assessed the effects of agonists selective for the mu-, delta-, and kappa-opioid receptors. The site of action (i.e., peripheral vs central) at which opioids produce immune changes was investigated by injecting the agonists directly into the left lateral ventricle of the brain. Specifically, Lewis rats received an intracerebroventricular administration of [d-Ala(2),N-Me-Phe(4), Gly-ol(5)]enkephalin (DAMGO), a mu-receptor selective agonist, [D-Pen(2,5)]enkephalin (DPDPE), a delta-opioid receptor agonist, or U69,593, a kappa-receptor agonist. Immune assessments completed 1 h following drug administration showed that the mu-receptor selective agonist DAMGO produced a dose-dependent decrease in natural killer cell activity and T-lymphocyte proliferation to the mitogen concanavalin A (Con A); no immunological changes were found following DPDPE or U69,593 treatment. Calculation of the number of white blood cells per sample showed no differences between rats treated with saline and rats treated with any of the selective agonists. Administration of the opioid antagonist N-methylnaltrexone prior to DAMGO treatment attenuated the DAMGO-induced changes in immune status. Results from the present study indicate that the immunomodulatory effects of opioids can be attributed to interactions with the mu-opioid receptor.

Heroin modulates the expression of inducible nitric oxide synthase

The use of heroin (diacetylmorphine) is associated with a high incidence of infectious disease, and the immunologic alterations responsible for heroin-induced changes in resistance to infection have not been well characterized. The present study tests the hypothesis that expression of inducible nitric oxide synthase (iNOS) is modulated by the administration of heroin. The initial study using rats showed that heroin administration (0, 0.01, 0.1, or 1.0 mg/kg s.c.) results in a pronounced reduction in lipopolysaccharide (LPS)-induced expression of iNOS mRNA in spleen, lung, and liver tissue as measured by RT-PCR. Heroin also produced a reduction in the level of plasma nitrite/nitrate, the more stable end-product of nitric oxide degradation. In a subsequent study, administration of the opioid receptor antagonist, naltrexone (0.1 mg/kg) prior to the injection of heroin (1.0 mg/kg) blocked the heroin-induced reduction of iNOS expression and plasma nitrite/nitrate levels indicating that the effect is mediated via the opioid-receptor. This study provides the first evidence that heroin induces an alteration of iNOS expression, and suggests that a reduction in nitric oxide production may be involved in the increased incidence of infectious diseases amongst heroin users.

Role of central mu-opioid receptors in the modulation of nitric oxide production by splenocytes

Previous studies have shown that administration of morphine results in alterations of splenic macrophage nitric oxide production. The present studies were conducted to determine the subtype of opioid receptor involved in the modulation of macrophage nitric oxide production. Moreover, the present work was directed at determining whether nitric oxide production is regulated through opioid receptors in the central nervous system (CNS) or via opioid receptors found directly on splenocytes. The study shows that intracerebroventricular (i.c.v.) administration of the mu-selective opioid agonist, DAMGO, to rats dose-dependently increases the production of nitric oxide by splenocytes stimulated with toxic shock syndrome toxin (TSST-1). The effect of DAMGO is blocked by prior i.c.v. administration of N-methylnaltrexone. In contrast, i.c.v. administration of the kappa-selective agonist, U69,593, and the delta-selective agonist, DPDPE, have no significant effect on the production of nitric oxide. Furthermore, the in vitro administration of DAMGO, DPDPE, or U69,593 to splenocytes cultures does not significantly alter the production of nitric oxide by splenocytes. In addition, the present work shows that elevation of nitric oxide production by i.c.v. administration of DAMGO produces functional changes in splenic lymphocytes. Collectively, these results indicate that mu-opioid receptors within the CNS are involved in the regulation of splenic nitric oxide production.

Inhibitory mechanisms of naloxone on human platelets

1. In the present study, naloxone was tested for its antiplatelet activities in human platelet-rich plasma (PRP). In human PRP, naloxone (0.1-0.5 mmol/L) inhibited aggregation stimulated by a variety of agonists (i.e. collagen, adenosine diphosphate (ADP), U46619 and adrenaline). 2. Naloxone (0.1-0.5 mmol/L) did not significantly affect cyclic adenosine monophosphate and cGMP levels in human washed platelets, whereas naloxone (0.5 mmol/L) significantly inhibited thromboxane B2 formation stimulated by collagen (5 micrograms/mL) in human washed platelets. 3. Naloxone (0.5 mmol/L) significantly inhibited [3H]-inositol monophosphate formation of [3H]-myoinositol-loaded platelets stimulated by collagen and U46619. Moreover, naloxone did not influence the binding of 125I-triflavin to platelet membranes. Triflavin is an Arg-Gly-Asp-containing specific fibrinogen receptor antagonist. 4. Addition of naloxone (0.5 mmol/L) to platelet preparations tagged with diphenylhexatriene (DPH) resulted in a considerable decrease in relative fluorescence intensity. 5. It is suggested that the anti-platelet effects of naloxone may be caused, at least partly, by the induction of conformational changes in the platelet membrane initially, followed by the inhibition of thromboxane A2 formation and phosphoinositide breakdown of platelets stimulated by agonists.

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

The literature describing effects of morphine on cells of the immune system points to the clear conclusion that morphine given in vivo suppresses a variety of immune responses that involve the major cell types in the immune system, including natural killer (NK) cells, T cells, B cells, macrophages and polymorphonuclear leukocytes (PMNs). Depression of NK cell activity has been reported in humans, monkeys and rodents. Similarly, responses of T cells are depressed by morphine, as assessed by inhibition of induction of delayed-type hypersensitivity reactions and cytotoxic T-cell activity, modulation of T-cell antigen expression, and depression of responses to T-cell mitogens. Effects on T cells have been reported in humans, monkeys and rodents. Effects of morphine on B-cell activity have mainly been tested in rodents using assays of antibody formation, which also require macrophages and T cells, preventing a conclusion as to the cell type being affected. Consistent effects on phagocytic cell function have been reported in rodents given morphine. In contrast, studies on immunomodulatory effects of morphine added to cells of the immune system in vitro have shown robust effects on some of these cell types, but not others. There is a rich literature demonstrating downregulation of phagocytic cell function by morphine, particularly for human peripheral blood mononuclear cells (PBMCs) and PMNs. Phagocytosis, chemotactic responses, interleukin production, and generation of activated oxygen intermediates and arachidonic acid products have all been reported to be inhibited. On the contrary, the literature does not support direct effects of morphine on NK cell function, is inconclusive concerning effects on B cells, and provides limited evidence for effects on T cells. The divergence between the in vivo and in vitro data suggests that effects on some cells in the immune system observed after in vivo morphine are probably not direct, but mediated. In aggregate, the literature supports the existence of an in vivo neural-immune circuit through which morphine acts to depress the function of all cells of the immune system. Further, there is strong evidence that morphine can directly depress the function of macrophages and PMNs, and modulate expression of one type of T-cell surface marker. There is, however, little evidence for direct effects of morphine on NK cells and B cells. A further complication emerges from reports of immunopotentiation of immune function in in vitro assays using endogenous opioids. The possibility of different receptors for endogenous and exogenous opioids or of interactions among the activated opioid receptors may account for these opposing effects.

Morphine induces splenocyte apoptosis and enhanced mRNA expression of cathepsin-B

Morphine has been demonstrated to modulate immune function. We studied whether morphine modulates apoptosis of splenocytes. Splenocytes were isolated from control and morphine treated rats. Splenocytes isolated from morphine treated rats showed increased percentage (P < 0.001) of apoptosis when compared to splenocytes isolated from untreated rats (control, 4.7 +/- 1.0% apoptotic splenocytes/field vs. morphine, 47.8 +/- 3.4% apoptotic splenocytes/field). These results were further confirmed by gel electrophoresis as well as by end-labeling DNA of splenocytes isolated from control and morphine treated rats. Splenocytes from morphine treated rats showed a classical ladder pattern with integer multiples of 180 base pairs. Splenocytes from morphine treated rats also showed increased mRNA expression of cathepsin-B, a gene associated with active cell death. These results suggest that morphine may also be modulating immune function by enhancing apoptosis of splenocytes.

Founder virus population related to route of virus transmission: a determinant of intrahost human immunodeficiency virus type 1 evolution?

We and others have shown that in individual human immunodeficiency virus type 1 (HIV-1) infection, the adaptive evolution of HIV-1 is influenced by host immune competence. In this study, we tested the hypothesis that in addition to selective forces operating within the host, transmission bottlenecks have an impact on HIV-1 intrahost evolution. Therefore, we studied the intrahost evolution of the V3 region of the external glycoprotein gp120 of HIV-1 during the 3- and 5-year periods following seroconversion after parenteral versus sexual (male-to-male) transmission in 41 participants of the Amsterdam prospective cohorts of homosexual men (n = 31) and intravenous drug users (IVDUs; n = 10) who were AIDS free and had comparable numbers of CD4+ cells. We observed that HIV-1 strains in homosexual men accumulated over 5 years more nonsynonymous substitutions within the V3 loop than HIV-1 strains in IVDUs as a result of lower rates of nonsynonymous evolution in both the initial 3-year period from seroconversion and the following 2-year period as well as a larger proportion of nonsynonymous back substitutions in IVDUs. The mean numbers of synonymous substitutions did not differ between the two risk groups. Since HIV-1 strains in IVDUs could be distinguished from the viruses of homosexual men based on several nucleotide substitutions of which the most conserved is a synonymous substitution at the tip of the V3 loop (GGC pattern), we studied whether the founder virus population itself has an impact on the intrahost evolution of HIV-1. The mean number of nonsynonymous substitutions accumulated over 5 years within the V3 loop was lower in 10 IVDUs infected by the HIV-1 strains with the GGC signature than in 4 IVDUs infected by HIV-1 strains lacking this pattern, while the mean numbers of synonymous substitutions were similar in the two groups.

Fluorescent staining of kappa opioid receptors using naltrexamine derivatives and phycoerythrin

An immunofluorescent technique that is more sensitive than radioligand binding was developed in order to detect opioid receptors expressed on leukocytes. The current study was designed to optimize the method for fluorescently labeling kappa opioid receptors. For these experiments, the opioid antagonist naltrexamine was conjugated to either fluorescein (FITC-NTXamine) or biotin (biotin-NTXamine). One-step, two-step, and three-step protocols were compared to determine which procedure resulted in optimal staining of the kappa opioid receptor expressed on intact, unfixed R1E/TL8x.1.OUAr.1(R1EGO) cells, a thymoma known to express kappa opioid receptors. The one-step method involved incubating cells with FITC-NTXamine, and the fluorescein intensity was measured by flow cytometry. In the two-step method, cells were incubated with biotin-NTXamine, followed by extravidin-conjugated phycoerythrin, and the phycoerythrin fluorescence was measured. Finally, in the three-step protocol, cells were incubated with FITC-NTXamine, followed by biotin-conjugated anti-fluorescein IgG, then extravidin-phycoerythrin. The one-step protocol stained the cells, but the signal was not diminished in the presence of opioid competitors. The two-step approach did not stain cells significantly above background levels. Only the three-step approach yielded staining that was displaced by the kappa-selective antagonist nor-binaltorphimine. Thus, the addition of a secondary biotinylated antibody, resulting in the amplification of binding, which was detected using phycoerythrin as a fluorophore, was required to detect low levels of opioid receptor expression on leukocytes.

Mechanism involved in the antiplatelet activity of naloxone in human platelets

In this study, naloxone was tested for its antiplatelet activity in human platelet suspensions. In platelet suspensions (4.5 x 10(8)/ml), naloxone (0.1-0.5 mM) significantly inhibited platelet aggregation and ATP-release stimulated by various agonists (i.e., thrombin, collagen, U46619, and ADP). Furthermore, naloxone (0.5 and 0.8 mM) dose-dependently inhibited the intracellular free Ca2+ rise of Fura 2-AM loaded platelets stimulated by collagen. Additionally, naloxone (0.5 and 1.0 mM) did not influence the binding of FITC-triflavin to platelet glycoprotein (GP) IIb/IIIa complex. On the other hand, naloxone (0.5 mM) markedly decreased the fluorescence of platelet membranes tagged with diphenylhexatriene (DPH). In addition, naloxone (0.1-0.5 mM) did not significantly affect cyclic-AMP levels in human washed platelets. It is concluded that the antiplatelet activity of naloxone may possibly be due to the induction of conformational changes in the platelet membrane and the inhibition of the intracellular Ca2+ ([Ca2+]i) mobilization as well as the release reaction of platelets stimulated by agonists.

Guanine nucleotide binding proteins in opioid-dependent patients

Guanine nucleotide binding (G) protein levels and functioning in the platelets of 19 methadone-maintained patients were compared to age and sex matched, normal controls. We found that in the methadone patients, G alpha s-levels were significantly higher, while the levels of G alpha i 1/2 and pertussis toxin catalyzed [32P]ADP ribosylation were significantly lower compared to control subjects in platelet membranes. We have further found that when all three of these biochemical indicators were combined in a discriminant function analysis, 79% of the methadone patients were correctly classified and 83% of the controls were correctly classified.

Enkephalins in hematopoiesis

Recent data support the view that neuropeptide mediators, in particular opioid peptides, participate in the control of hematopoiesis. The main arguments are: neuropeptides modulate the functions of lymphoid cells, macrophages and mature granulocytes; they control cell proliferation and differentiation in many tissues, particularly during embryogenesis; lymphoid cells, macrophages, polymorphonuclear granulocytes and bone marrow stromal elements express neuropeptide receptors; bone marrow cells produce opioid-like neuropeptides; the CD10/CALLA marker of lymphoid, myeloid and marrow stromal cells is an enzyme, endopeptidase, which cleaves- and thus activates/inactivates-opioid and other neuropeptides. We have shown that opioid peptides enkephalins, opioid antagonist naloxone, and the inhibitor of enkephalin-degrading endopeptidase, thiorphan, modulate the proliferation and differentiation of hematopoietic cells in clonal and long-term cultures of mouse bone marrow. The effects partly depended on the presence of the accessory hematopoietic elements, and followed a circadian pattern. The dose-responses were irregular, showed strain-dependent and individual variations, and apparently reflected the state of the activity of target cells, cellular interactions and simultaneous signals by other mediators. The enkephalins were shown to bind to specific (opioid) receptors on the target cells, and their signals to be transmitted to the cell interior by a cascade of secondary messengers including diacyl-glycerol (DAG), protein-kinase C (PKC) and Ca++ ions. Neuropeptide regulation of hematopoiesis might belong to a complex immuno-neuroendocrine network including melatonin.

Role of prolactin in the modulation of NK and LAK cell activity after short- or long-term morphine administration in neoplastic patients

In a previous work we demonstrated that chronic in vivo antalgic therapy of cancer patients with morphine reduced the endogenous cytotoxic activity of natural killer (NK) cells, while increasing the development of lymphokine activated killer (LAK) cell cytotoxicity. In order to investigate the mechanisms by which morphine affects NK and LAK cell function further, we evaluated the modulation exerted by short- or long-term morphine administration on either NK/LAK cell cytotoxicities or plasma levels of prolactin (PRL) and other immunomodulating neurohormones. An intravenous morphine injection (10 mg) significantly increased the plasma levels of PRL, reduced the cytotoxic activity of NK cells, and increased the development of LAK cell activity 30 min after drug injection in neoplastic patients. The administration of bromocriptine before the injection of morphine prevented both PRL augmentation and the increase in LAK cell activation, although it did not prevent the inhibition of NK cytotoxicity. The chronic oral administration of morphine (90 +/- 30 mg/day for 1 month) also resulted in higher PRL levels; the NK and LAK cell activities were, respectively, lower than or higher than those found in neoplastic patients untreated with morphine. The plasma levels of thyrotropin (TSH), adrenocorticotropic hormone (ACTH) and cortisol were not significantly modified in either short- or long-term experiments. The absolute number and the percentages of lymphocyte populations, as well as the percentage of IL-2 receptors, were not modified after short-term morphine administration whereas little changes of T lymphocyte populations and NK cell number were observed after oral treatment with morphine. In vitro morphine did not affect the development of LAK cell activity. In conclusion, our findings indicate that morphine reduces NK cytotoxicity and increases the development of LAK cell cytotoxicity after short- and long-term administration. The effect of morphine on LAK cell activation but not on NK cell reduction is related to the modulation of PRL levels determined by the opioid drug.