Cardiorespiratory anomalies and increased brainstem microglia in a rat model of neonatal opioid withdrawal syndrome.

Infants born with neonatal opioid withdrawal syndrome (NOWS) can display abnormal cardiorespiratory patterns including tachypnea, tachycardia, and impaired ventilatory responses to hypoxia (HVR) and hypercapnia (HCVR). Chronic morphine exposure is associated with increased midbrain microglial expression. Using a rat model of pre- and post-natal morphine exposure, we assessed cardiorespiratory features of NOWS (resting tachycardia and tachypnea) including the attenuated HVR and HCVR and whether they are associated with increased brainstem microglia expression. Pregnant rats (dams) received twice-daily subcutaneous injections of morphine (5 mg/kg) during the third (last) week of pregnancy to simulate 3rd trimester in utero opioid exposure. Offspring then received once-daily subcutaneous injections of morphine (0.5 mg/kg) until postnatal (P) day P10 days of age to simulate postnatal morphine therapy. Cardiorespiratory responses were assessed 24 h later (P11 days) following spontaneous withdrawal. Compared to saline-treated pups, morphine-exposed offspring exhibited tachycardia and tachypnea as well as an attenuated HVR and HCVR. Microglial cell counts were increased in the nucleus tractus solitarius (nTS), dorsal motor nucleus of the vagus (DMNV) and nucleus ambiguous (NAamb), but not the retrapezoid nucleus (RTN) or the non-cardiorespriatory region, the cuneate nucleus (CN). These data suggest that the cardiorespiratory features and autonomic dysregulation in NOWS infants may be associated with altered microglial function in specific brainstem cardiorespiratory control regions.

Integration of Molecular Inflammatory Interactome Analyses Reveals Dynamics of Circulating Cytokines and Extracellular Vesicle Long Non-Coding RNAs and mRNAs in Heroin Addicts During Acute and Protracted Withdrawal.

Heroin addiction and withdrawal influence multiple physiological functions, including immune responses, but the mechanism remains largely elusive. The objective of this study was to investigate the molecular inflammatory interactome, particularly the cytokines and transcriptome regulatory network in heroin addicts undergoing withdrawal, compared to healthy controls (HCs). Twenty-seven cytokines were simultaneously assessed in 41 heroin addicts, including 20 at the acute withdrawal (AW) stage and 21 at the protracted withdrawal (PW) stage, and 38 age- and gender-matched HCs. Disturbed T-helper(Th)1/Th2, Th1/Th17, and Th2/Th17 balances, characterized by reduced interleukin (IL)-2, elevated IL-4, IL-10, and IL-17A, but normal TNF-α, were present in the AW subjects. These imbalances were mostly restored to the baseline at the PW stage. However, the cytokines TNF-α, IL-2, IL-7, IL-10, and IL-17A remained dysregulated. This study also profiled exosomal long non-coding RNA (lncRNA) and mRNA in the plasma of heroin addicts, constructed co-expression gene regulation networks, and identified lncRNA-mRNA-pathway pairs specifically associated with alterations in cytokine profiles and Th1/Th2/Th17 imbalances. Altogether, a large amount of cytokine and exosomal lncRNA/mRNA expression profiling data relating to heroin withdrawal was obtained, providing a useful experimental and theoretical basis for further understanding of the pathogenic mechanisms of withdrawal symptoms in heroin addicts.

Sexually dimorphic neuroimmune response to chronic opioid treatment and withdrawal.

Opioid use disorder is a leading cause of morbidity and mortality in the United States. Increasing pre-clinical and clinical evidence demonstrates sex differences in opioid use and dependence. However, the underlying molecular mechanisms contributing to these effects, including neuroinflammation, are still obscure. Therefore, in this study, we investigated the effect of oxycodone exposure and withdrawal on sex- and region-specific neuroimmune response. Real-time PCR and multiplex cytokine array analysis demonstrated elevated neuroinflammation with increased pro-inflammatory cytokine levels, and aberrant oligodendroglial response in reward neurocircuitry, following withdrawal from chronic oxycodone treatment. Chronic oxycodone and withdrawal treated male mice had lower mRNA expression of TMEM119 along with elevated protein levels of pro-inflammatory cytokines/chemokines and growth factors (IL-1ß, IL-2, IL-7, IL-9, IL-12, IL-15, IL17, M-CSF, VEGF) in the prefrontal cortex (PFC) as compared to their female counterparts. In contrast, reduced levels of pro-inflammatory cytokines/chemokines (IL-1ß, IL-6, IL-9, IL-12, CCL11) was observed in the nucleus accumbens (NAc) of oxycodone and withdrawal-treated males as compared to female mice. No treatment specific effects were observed on the mRNA expression of putative microglial activation markers (Iba1, CD68), but an overall sex specific decrease in the mRNA expression of Iba1 and CD68 was found in the PFC and NAc of male mice as compared to females. Moreover, a sex and region-specific increase in the mRNA levels of oligodendrocyte lineage markers (NG2, Sox10) was also observed in oxycodone and withdrawal treated animals. These findings may open a new avenue for the development of sex-specific precision therapeutics for opioid dependence by targeting region-specific neuroimmune signaling.

[Alcoholization and ethanol withdrawal leads to the activation of neuroimmune response in the prefrontal rat brain]. / Alkogolizatsiia i otmena étanola privodiat k aktivatsii neiroimmunnogo otveta v prefrontal'noi kore mozga krys.

The effects of acute (single) and chronic ethanol administration on the level of pro-inflammatory cytokines (IL-1ß and TNF-α), as well as on the level of mRNA NF-κB, TLR4 and its endogenous agonist, HMGB1 protein, were investigated in rats. It was shown that the level of TLR4, HMGB1 and cytokines was significantly higher than in control group. The ethanol withdrawal after prolonged administration resulted in dysregulation of cytokine levels, TLR4 and HMGB1. Changes in the level of TLR4 and HMGB1 mRNA demonstrated a similar pattern. The obtained data confirm that prolonged alcoholization leads to the activation of TLR4-dependent signaling in the prefrontal cortex of rats, and this can lead to a prolonged neuro-inflammatory process in the brain.

Peripheral blood lymphocyte subsets change after steroid withdrawal in renal allograft recipients: a prospective study.

Several studies have assessed clinical outcomes after steroid withdrawal (SW) in kidney transplant (KT) recipients, but little is known about its potential impact on lymphocyte subpopulations. We designed a prospective study to evaluate the long-term impact of SW in 19 KT recipients compared to 16 KT recipients without changes in immunosuppression (steroid maintenance, SM). We assessed renal function, presence of HLA antibodies and peripheral blood lymphocyte subsets at time of inclusion, and 3, 12 and 24 months later. The immunophenotype of 20 healthy subjects was also analyzed. Serum creatinine and proteinuria remained stable in SW and SM patients. SW did not associate with generation of de novo donor-specific antibodies. SW patients showed decreases in T-lymphocytes (p < 0.001), and in the CD4+ T cell subpopulation (p = 0.046). The proportion of B-lymphocytes (p = 0.017), and both naïve and transitional B cells increased compared to SM patients (p < 0.001). Changes in B cell subsets were detected 3 months after SW and persisted for 24 months. No changes were observed in NK cells related to steroid withdrawal. SW patients displayed significant changes in peripheral T and B cell subsets, transitioning to the phenotype detected in healthy subjects. This may be considered as a maintained positive effect of SW previously unnoticed.

From Traumatic Childhood to Cocaine Abuse: The Critical Function of the Immune System.

BACKGROUND: Experiencing traumatic childhood is a risk factor for developing substance use disorder, but the mechanisms that underlie this relationship have not been determined. Adverse childhood experiences affect the immune system, and the immune system mediates the effects of psychostimulants. However, whether this system is involved in the etiology of substance use disorder in individuals who have experienced early life stress is unknown. METHODS: In this study, we performed a series of ex vivo and in vivo experiments in mice and humans to define the function of the immune system in the early life stress-induced susceptibility to the neurobehavioral effects of cocaine. RESULTS: We provide evidence that exposure to social stress at an early age permanently sensitizes the peripheral (splenocytes) and brain (microglia) immune responses to cocaine in mice. In the brain, microglial activation in the ventral tegmental area of social-stress mice was associated with functional alterations in dopaminergic neurotransmission, as measured by whole-cell voltage clamp recordings in dopamine neurons. Notably, preventing immune activation during the social-stress exposure reverted the effects of dopamine in the ventral tegmental area and the cocaine-induced behavioral phenotype to control levels. In humans, cocaine modulated toll-like receptor 4-mediated innate immunity, an effect that was enhanced in those addicted to cocaine who had experienced a difficult childhood. CONCLUSIONS: Collectively, our findings demonstrate that sensitization to cocaine in early life-stressed individuals involves brain and peripheral immune responses and that this mechanism is shared between mice and humans.

Delayed Autoimmune Toxicity Occurring Several Months After Cessation of Anti-PD-1 Therapy.

Treatment with anti-programmed cell death protein 1 (PD-1) antibodies has demonstrated clinical efficacy in a whole range of malignancies including advanced melanoma, renal cell cancer, bladder cancer, and non-small cell lung cancer. Immune-related adverse events are a unique side effect of checkpoint regulator therapy including anti-PD-1 antibodies. Treatment-related autoimmunity can occur in any organ system, with the median onset usually within 5-15 weeks from the commencement of therapy, depending on the organ system involved. This study describes for the first time a case of delayed autoimmunity occurring 8 months after discontinuing treatment with the anti-PD-1 antibody nivolumab in a patient with metastatic melanoma. The case highlights the need for ongoing surveillance of patients treated with immune checkpoint inhibitors even after cessation of therapy, especially as patients increasingly stop treatment after achieving durable responses.

Peripheral immune system suppression in early abstinent alcohol-dependent individuals: Links to stress and cue-related craving.

BACKGROUND: Peripheral immune system cytokines may play an integral role in the underlying sensitized stress response and alcohol craving during early alcohol withdrawal. To date, the nature of these immune changes during early abstinence have not been examined. METHODS: A total of 39 early abstinent, treatment-seeking, alcohol-dependent individuals and 46 socially drinking controls were exposed to three guided imageries: stress, alcohol cue and neutral. These were presented randomly across consecutive days. Plasma measures of tumor necrosis factor alpha (TNFα), tumor necrosis factor receptor 1 (TNFR1), interleukin-6 (IL-6), and interleukin-10 (IL-10), were collected at baseline, immediately after imagery and at various recovery time-points. Ratings of alcohol craving, negative mood and anxiety were also obtained at the same time-points. RESULTS: The alcohol group demonstrated decreased basal IL-10 compared with controls particularly following exposure to alcohol cue. They also showed a dampened TNFα and TNFR1 response to stress and cue, respectively, and a generalized suppression of IL-6. In the alcohol group, these immune system adaptations occurred alongside significant elevations in anxiety, negative mood and alcohol craving. CONCLUSIONS: Findings demonstrate that broad immunosuppression is still observed in alcohol-dependent individuals after 3 weeks of abstinence and may be linked to motivation for alcohol.

Effects of alcohol withdrawal on monocyte subset defects in chronic alcohol users.

Excessive alcohol consumption has a modulating effect on immune functions that may contribute to decreased immunity and host defense. It is associated with increased intestinal permeability to endotoxins that is normalized after 14 d of abstinence. Whether and how blood monocyte subsets are impaired in patients with an AUD and what their evolution is after alcohol withdrawal are the paper's objectives. With the use of flow cytometry, blood monocyte subsets were quantified in AUDs before (n = 40) and 2 wk after (n = 33) alcohol withdrawal and compared with HC donors (n = 20). Expression of TLR2 and TLR4 on monocyte subsets was also quantified. Cytokine response of monocytes was monitored following PGN and LPS stimulation. The CD14+CD16- subset was decreased, whereas the CD14dimCD16+ subset was expanded (P < 0.001) in AUD compared with HC. The frequencies of TLR2- and TLR4-expressing monocytes were reduced in AUD compared with HC. Although the basal production of IL-1, IL-6, and TNF by monocytes in AUD was compared with HC, the PGN- and LPS-mediated IL-6 and TNF production was increased in AUD. Frequencies of IL-6-expressing monocytes were higher in AUD than HC. Alcohol withdrawal partially restored the distribution of monocyte subsets and the frequency of IL-6-producing monocytes and increased the frequency of TNF-producing cells in response to LPS and PGN stimulation to levels compared with those in HC. Our findings indicate that chronic alcohol use alters the distribution as well as the phenotypic and functional characteristics of blood monocyte subsets, which are partially restored following 2 wk of alcohol withdrawal.

Persistent adaptation by chronic alcohol is facilitated by neuroimmune activation linked to stress and CRF.

This review updates the conceptual basis for the association of alcohol abuse with an insidious adaptation that facilitates negative affect during withdrawal from chronic intermittent alcohol (CIA) exposure - a change that later supports sensitization of stress-induced anxiety following alcohol abstinence. The finding that a CRF1-receptor antagonist (CRF1RA) minimized CIA withdrawal-induced negative affect supported an association of alcohol withdrawal with a stress mechanism. The finding that repeated stresses or multiple CRF injections into selected brain sites prior to a single 5-day chronic alcohol (CA) exposure induced anxiety during withdrawal provided critical support for a linkage of CIA withdrawal with stress. The determination that CRF1RA injection into positive CRF-sensitive brain sites prevented CIA withdrawal-induced anxiety provided support that neural path integration maintains the persistent CIA adaptation. Based upon reports that stress increases neuroimmune function, an effort was undertaken to test whether cytokines would support the adaptation induced by stress/CA exposure. Twenty-four hours after withdrawal from CIA, cytokine mRNAs were found to be increased in cortex as well as other sites in brain. Further, repeated cytokine injections into previously identified brain sites substituted for stress and CRF induction of anxiety during CA withdrawal. Discovery that a CRF1RA prevented the brain cytokine mRNA increase induced by CA withdrawal provided critical evidence for CRF involvement in this neuroimmune induction after CA withdrawal. However, the CRF1RA did not block the stress increase in cytokine mRNA increases in controls. The latter data supported the hypothesis that distinct mechanisms linked to stress and CA withdrawal can support common neuroimmune functions within a brain site. As evidence evolves concerning neural involvement in brain neuroimmune function, a better understanding of the progressive adaptation associated with CIA exposure will advance new knowledge that could possibly lead to strategies to combat alcohol abuse.

[Autoantibodies to Neuropeptides in the Different States of Opium Addiction].

Background: During the last years the addiction rate remains stable high. While the neurochemical drug effect remains unclear. Aims: To analyze the changes of the idiotypic (аАТ1) and anti-idiotypic (аАТ2) autoantibodies to the neuroproteins S100, MBP, GFAP, NGF on the different stages of opium addiction and to indicate prognosis criteria of their effect. Materials and Methods: 70 patients (only men, aged 22−38) with diagnosis opium addiction underwent examination. According to the results of testing, we detected the intoxication in 24 patients, withdrawal ­ in 24, and 22 patients were at remission stage of 21−28 days. The control group included only healthy people (n=18). The survey was focused on the rate detection of the idiotypic and anti-idiotypic IgG class antibodies in relation to the rate of neural proteins (S100, MBP, GFAP, NGF) in the serum with the IEA. Results: In patients with opium intoxication, we revealed statistical assurance in the rate of autoantibodies amount and their counterweights to the neural proteins rate between control and experimental groups. Only the rate of the аАТ2 protein significantly decreased relatively to the MBP. In patients with abstinence, the rate of аАТ1 to the MBP, GFAP (р≤0,05) increased. The rate of аАТ2 in relation to the GFAP and MBP also increased (р≤0,05), at the same time it decreased in relation to the S100 and NGF (р≤0,05). The autoantibodies amount at the remission stage corresponded to the amount at the intoxication stage. The comparative analysis of the patient groups with the different stages of opium addiction detected the identity criteria both in the intoxication and remission. We revealed statistical assurance in the rates of аАТ1 to MBP and аАТ2 to NGF in patients with intoxication and abstinence, and in the rates of аАТ1 to GFAP, MBP, and аАТ2 to GFAP (decreased in the remission) and to S100, MBP (increased in the remission) in patients with abstinence and at remission. Conclusion: Levels of idiotypic and anti-idiotypic antibodies to the neural proteins S100, MBP, GFAP, NGF (especially аАТ2 to MPB) could be used as diagnostic factor and for accessing different states of opium addiction.

Neuroimmune Regulation of GABAergic Neurons Within the Ventral Tegmental Area During Withdrawal from Chronic Morphine.

Opioid dependence is accompanied by neuroplastic changes in reward circuitry leading to a negative affective state contributing to addictive behaviors and risk of relapse. The current study presents a neuroimmune mechanism through which chronic opioids disrupt the ventral tegmental area (VTA) dopaminergic circuitry that contributes to impaired reward behavior. Opioid dependence was induced in rodents by treatment with escalating doses of morphine. Microglial activation was observed in the VTA following spontaneous withdrawal from chronic morphine treatment. Opioid-induced microglial activation resulted in an increase in brain-derived neurotrophic factor (BDNF) expression and a reduction in the expression and function of the K(+)Cl(-) co-transporter KCC2 within VTA GABAergic neurons. Inhibition of microglial activation or interfering with BDNF signaling prevented the loss of Cl(-) extrusion capacity and restored the rewarding effects of cocaine in opioid-dependent animals. Consistent with a microglial-derived BDNF-induced disruption of reward, intra-VTA injection of BDNF or a KCC2 inhibitor resulted in a loss of cocaine-induced place preference in opioid-naïve animals. The loss of the extracellular Cl(-) gradient undermines GABAA-mediated inhibition, and represents a mechanism by which chronic opioid treatments can result in blunted reward circuitry. This study directly implicates microglial-derived BDNF as a negative regulator of reward in opioid-dependent states, identifying new therapeutic targets for opiate addictive behaviors.

Immune Function Alterations during 12 Weeks of Abstinence in Heroin Users.

The intent of the study was to evaluate immune system changes during 12 weeks of abstinence in heroin users. We recruited men (N = 65) aged 18-45 years and collected demographic and heroin use pattern data. Serum blood levels of total interleukin 2 (IL-2), interferon γ (IFN-γ), immunoglobulin (Ig) A, IgG, and IgM were assessed at five time points. The IL-2 level was increased on day 84 as compared to that in healthy controls. The IFN-γ level was higher in heroin users than in healthy controls between days 0 and 28, and was decreased on day 84. IgG and IgM levels in heroin users were higher than those in healthy controls in our 12-week study, and were in positive correlation with the way of using the drug, duration of heroin dependence, and daily heroin intake. Our data revealed that the immune system was not restored during the 12 weeks of heroin withdrawal.

[Antibodies to neurotransmitters as possible neuroimmune risk markers of formation dependence to psychoactive substances].

In the sera of patients with opioid addiction has been found elevated levels of autoantibodies to the neurotransmitters dopamine, norepinephrine and serotonin in comparison with a control group of healthy people of the same age. In the group of patients with acute withdrawal was showed a reduction of antibody to dopamine, noradrenaline and serotonin in the blood serum when compared with patients in the period of postabstinent disorders. In the group of patients with risk for the formation of substance dependence in serum was observed decrease in autoantibodies to dopamine and norepinephrine compared with the control group.

Predictive factors of allosensitization after immunosuppressant withdrawal in recipients of long-term cultured islet cell grafts.

BACKGROUND: Islet transplantation has been reported to induce allosensitization in the majority of type 1 diabetic recipients of fresh or shortly incubated islet grafts prepared from one to three donors. METHODS: We examined the appearance of human leukocyte antigen (HLA) antibodies after withdrawal of immunosuppressants in 35 type 1 diabetic recipients of islet cell grafts prepared from a median of 6 donors (range, 2-11), cultured for longer periods, and characterized for their cellular composition. Immunosuppression consisted of antithymocyte globulin induction followed by mycophenolate mofetil plus calcineurin inhibitors (n=28, with 7 also receiving steroids) or sirolimus with (n=3) or without calcineurin inhibitors (n=4). Both the complement-dependent cytotoxicity (CDC) assay (class I) and the solid-phase flow-based Luminex method (class I and II) were used to identify HLA antibodies. RESULTS: Immunosuppressant withdrawal resulted in CDC positivity for class I antibodies in only 6% of patients. However, the majority became positive for class I antibodies (72%) or class II antibodies (72%) in the Luminex assay; positivity was not correlated to a higher number of donors or HLA mismatches, but with a lower ß-cell purity; use of steroids reduced de novo positivity for Luminex class I antibodies. CONCLUSION: Allosensitization to cultured human islet cell grafts was low when assessed by CDC assay but high in Luminex. No correlation was found with the number of donors but risk was higher for grafts with lower ß-cell purity.

Relapse is almost universal after withdrawal of immunosuppressive medication in patients with autoimmune hepatitis in remission.

BACKGROUND & AIMS: Current treatment strategies in autoimmune hepatitis (AIH) include long-term treatment with corticosteroids and/or azathioprine. Here we determined the risk of relapse after drug withdrawal in patients in long-term remission and factors associated with such a relapse. METHODS: A total of 131 patients (out of a cohort including 844 patients) from 7 academic and 14 regional centres in the Netherlands were identified in whom treatment was tapered after at least 2 years of clinical and biochemical remission. Relapse was defined as alanine-aminotransferase levels (ALT) three times above the upper limit of normal and loss of remission as a rising ALT necessitating the reinstitution of drug treatment. RESULTS: During follow-up, 61 (47%) patients relapsed and 56 (42%) had a loss of remission. In these 117 patients, 60 patients had fully discontinued medication whereas 57 patients were still on a withdrawal scheme. One year after drug withdrawal, 59% of the patients required retreatment, increasing to 73% and 81% after 2 and 3 years, respectively. Previous combination therapy of corticosteroids and azathioprine, a concomitant autoimmune disease and younger age at time of drug withdrawal were associated with an increased risk of relapse. Subsequent attempts for discontinuation after initial failure in 32 patients inevitably resulted in a new relapse. CONCLUSIONS: This retrospective analysis indicates that loss of remission or relapse occurs in virtually all patients with AIH in long-term remission when immunosuppressive therapy is discontinued. These findings indicate a reluctant attitude towards discontinuation of immunosuppressive treatment in AIH patients.

Temporal changes in innate immune signals in a rat model of alcohol withdrawal in emotional and cardiorespiratory homeostatic nuclei.

BACKGROUND: Chronic alcohol use changes the brain's inflammatory state. However, there is little work examining the progression of the cytokine response during alcohol withdrawal, a period of profound autonomic and emotional upset. This study examines the inflammatory response in the central nucleus of the amygdala (CeA) and dorsal vagal complex (DVC), brain regions neuroanatomically associated with affective and cardiorespiratory regulation in an in vivo rat model of withdrawal following a single chronic exposure. METHODS: For qRT-PCR studies, we measured the expression of TNF-α, NOS-2, Ccl2 (MCP-1), MHC II invariant chain CD74, and the TNF receptor Tnfrsf1a in CeA and DVC samples from adult male rats exposed to a liquid alcohol diet for thirty-five days and in similarly treated animals at four hours and forty-eight hours following alcohol withdrawal. ANOVA was used to identify statistically significant treatment effects. Immunohistochemistry (IHC) and confocal microscopy were performed in a second set of animals during chronic alcohol exposure and subsequent 48-hour withdrawal. RESULTS: Following a chronic alcohol exposure, withdrawal resulted in a statistically significant increase in the expression of mRNAs specific for innate immune markers Ccl2, TNF-α, NOS-2, Tnfrsf1a, and CD74. This response was present in both the CeA and DVC and most prominent at 48 hours. Confocal IHC of samples taken 48 hours into withdrawal demonstrate the presence of TNF-α staining surrounding cells expressing the neural marker NeuN and endothelial cells colabeled with ICAM-1 (CD54) and RECA-1, markers associated with an inflammatory response. Again, findings were consistent in both brain regions. CONCLUSIONS: This study demonstrates the rapid induction of Ccl2, TNF-α, NOS-2, Tnfrsf1a and CD74 expression during alcohol withdrawal in both the CeA and DVC. IHC dual labeling showed an increase in TNF-α surrounding neurons and ICAM-1 on vascular endothelial cells 48 hours into withdrawal, confirming the inflammatory response at the protein level. These findings suggest that an abrupt cessation of alcohol intake leads to an acute central nervous system (CNS) inflammatory response in these regions that regulate autonomic and emotional state.

Withdrawal from morphine reduces cell-mediated immunity against herpes simplex virus generated by natural immunization.

In a previous study, the authors have shown that herpes simplex virus type 1 (HSV-1) glycoprotein B DNA vaccine but not live vaccine (non-virulent KOS strain) failed to induce protective immunity against acute HSV-1 challenge in morphine-dependent mice. The present study reports the effect of morphine withdrawal on protective immunity induced by live HSV-1 immunization. BALB/c mice were vaccinated with KOS strain as a live vaccine. Three weeks later, they were exposed to morphine for 14 days. On day 14, withdrawal was induced by administration of normal saline instead of morphine. One day later, immune responses against HSV-1 were assessed by measuring cytotoxicity, lymphocyte proliferation and interferon-γ production. Protection against HSV-1 was assessed by measuring the mortality rate after acute HSV-1 challenge. The results showed that withdrawal from morphine reduces protective immunity against acute HSV-1 challenge. These findings raise the possibility that withdrawal from morphine may increase the susceptibility of drug addicts to infectious diseases.