Acute exposure to morphine suppresses cytotoxic T-lymphocyte activity.

Chronic exposure (11 days) to morphine has previously been shown to suppress splenic and peritoneal cytotoxic T-lymphocyte activity through mu-opioid receptors. The present study was undertaken to assess the effects of varying the frequency of exposure to morphine on cytotoxic T-lymphocyte activity in C3H/HeN mice immunized with C57BL/6 splenocytes. Mice subchronically treated with morphine (50.0 mg/kg) showed no measurable suppression of splenic natural killer activity or splenic or peritoneal cytotoxic T-lymphocyte activity. However, mice treated acutely with 50.0 mg/kg of morphine exhibited a significant suppression of peritoneal but not splenic cytotoxic T-lymphocyte activity. Naltrexone pretreatment of mice receiving an acute dose of morphine blocked the suppression, implicating the involvement of opioid receptors. Using column depletion chromatography, peritoneal exudate cells mediating cytotoxic T-lymphocyte activity were both CD4+CD8- and CD4-CD8+. Collectively, the results suggest that the duration of opioid (morphine) exposure differentially affects peritoneal cytotoxic T-lymphocyte activity. These results may have important implications regarding immunity to viral infections in individuals who abuse drugs such as heroin.

Chronic & infrequent opioid exposure suppresses IL-2R expression on rhesus monkey peripheral blood mononuclear cells following stimulation with pokeweed mitogen.

In the present investigation, infrequent and chronic (daily) exposure of rhesus monkeys to morphine was investigated for their effect on cytokine receptor expression, interleukin (IL)-2-production, and the nuclear factor kappa B (NF kappa B) levels following stimulation with PWM. In a time-dependent manner, peripheral blood mononuclear cells (PBMCs) from both infrequent- and daily-morphine treated monkeys displayed significantly less (40 +/- 7%) IL-2 receptor compared to PBMCs from saline-treated controls. However, PBMCs from chronic opioid- and infrequent opioid-treated monkeys displayed similar levels of IL-4 and IL-7 receptors compared to saline-treated animals. Following stimulation with PWM, PBMCs from chronic opioid-treated monkeys produced elevated levels of IL-2 (870 +/- 94 pg/ml) compared to IL-2 levels (463 +/- 88 pg/ml) of PBMCs from saline-treated monkey. Likewise, PBMCs from chronic-morphine exposed monkeys had elevated levels (43%) of NF kappa B compared to PBMCs from saline-treated (control) monkeys following 72 hours in culture with PWM. Collectively, these observations suggest morphine regulates selective molecular events that manifest in biologically altered immune function including T cell activation and IL-2 production.

Pretreatment with beta-funaltrexamine blocks morphine-mediated suppression of CTL activity in alloimmunized mice.

The effect of prolonged exposure to morphine on cytotoxic T lymphocytes (CTL) and splenic natural killer (NK) activity was investigated. Daily administration of morphine (50.0 mg/kg, s.c.) to alloimmunized mice for 11 days resulted in a significant decrease (25-50%) in peritoneal and splenic CTL activity but not splenic NK activity. To identify the effector cell population mediating cytolysis, cell enrichment studies were carried out. The results of these studies indicated the CTLs are CD8+ CD4-. Chronic morphine treatment increased the percentage (25-30%) of CD3+ CD4+ and CD8+, but not Ig+ cells in the spleen relative to saline-treated controls. Pretreatment of mice with the mu-selective antagonist, beta-funaltrexamine blocked morphine-mediated suppression of splenic and peritoneal CTL activity as well as the increase in CD3+ CD4+ and CD8+ splenic lymphocytes. These results indicate the generation of CTLs in vivo is sensitive to chronic morphine exposure implicating opiates as important co-factors through modulation of cell-mediated immunity.

Morphine-induced suppression of cytotoxic T lymphocyte activity in alloimmunized mice is not mediated through a naltrindole-sensitive delta opioid receptor.

The effect of chronic morphine exposure on natural killer (NK) activity in vivo and the generation of cytotoxic T lymphocytes (CTLs) in vitro and in vivo was investigated. Chronic exposure to morphine (10(-5) - 10(-11) M) in vitro had no effect on the generation of antigen-driven effector cells. However, the daily administration of morphine (50.0 mg/kg, s.c.) into alloimmunized mice (C57BL/6 into C3H/HeN) for 11 days resulted in a decrease in peritoneal and splenic CTL activity but not splenic NK activity. In addition, there was a 60% decrease in the number of thymocytes recovered from chronic morphine-treated mice compared to vehicle-treated controls. However, the overall percentage of CD4+CD8-, CD4-CD8+ and CD4+CD8+ thymocytes did not change between the two groups of treated animals. Pretreatment of the mice with the delta 1-selective antagonist, (E)-7-benzylidine-7-dihydronaltrexone (BNTX, 0.6 mg/kg, s.c.) did not block morphine-mediated suppression of splenic CTL activity but did block morphine-induced suppression of peritoneal lymphocyte CTL activity. In addition, BNTX pretreatment alone augmented splenic NK activity and such augmentation was blocked following chronic morphine exposure. In contrast, the delta-selective antagonist, naltrindole (20.0 mg/kg, s.c.), had no effect alone nor antagonized the action of morphine on CTL activity. Splenic CTL effector cells from either treated group of animals lysed their target (EL-4 lymphoma) through a Ca(2+)-dependent mechanism. Collectively, the results indicate morphine suppresses CTL activity through an indirect pathway, insensitive to naltrindole rather than through direct lymphocyte opioid receptors.

Cellular mechanisms involved in morphine-mediated suppression of CTL activity.

Based on a plethora of data from many laboratories, we have proposed the following mechanisms by which morphine alters immune homeostasis and immunocompetence in vivo (Fig. 2). Specifically, the administration of morphine subcutaneously via routing through blood interacts directly with opioid receptors on cells of the immune system or on receptors within the central nervous system. Although there is currently no evidence to support the direct involvement of morphine on lymphocyte opioid receptors, in vitro studies show the existence of functional, naloxone-sensitive opioid receptors (25). In addition, pharmacological and biochemical characterization of lymphocyte opioid receptors has been shown to be consistent in many instances, with the profile of neural-derived opioid receptors (25-27). Finally, recent molecular studies using oligonucleotide primers specific for the delta-class opioid receptor cloned from NG-108-15 cells (28) have been used in reverse transcription-polymerase chain reactions to generate a 400 bp product in SL which has 100% sequence homology with a published opioid receptor cloned from a brain library (35). However, future studies are necessary to establish the role of lymphocyte opioid receptors following the in vivo administration of opioids (e.g. fentanyl, methadone, and morphine). Since the administration of morphine subcutaneously appears to predominately interact with brain opioid receptors (3) located in the mesencephalon (5), other neuroendocrine systems become candidates for activation and subsequent direct modulation of immune function: (i) the HPA axis and (ii) the sympathetic nervous system (SNS).(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic morphine treatment suppresses CTL-mediated cytolysis, granulation, and cAMP responses to alloantigen.

Exposure to opioid drugs (e.g., morphine) in vivo has been shown to suppress natural killer cell activity. However, the effects of in vivo exposure to opioids on cytotoxic T lymphocyte (CTL) activity has not been investigated. The administration of morphine (50.0 mg/kg, sc) to alloimmunized mice for 11 days resulted in a significant decrease in peritoneal and splenic CTL activity. Moreover, the intracellular content of serine esterases and esterase release by CD8+ effector cells from chronic morphine-treated mice was reduced compared to that of effector cells from vehicle-treated controls. In addition, the CD8+ cAMP response to alloantigen was diminished compared to CD(8+)-enriched cells from vehicle-treated animals. However, conjugate formation between effector and target and subsequent killing of target by effector cells did not reveal significant differences between vehicle- and chronic morphine-treated animals. Serum corticosterone and dehydroepiandrosterone levels were significantly lower in the chronic morphine-treated animals while proopiomelanocortin gene expression (exon 3) in splenic lymphocytes did not correlate with morphine-mediated suppression of CTL activity. These results indicate that CTL activity is sensitive to chronic morphine exposure, implicating opioids as important cofactors during viral infections in suppressing cell-mediated immunity.