Morphine-induced alterations in antibody levels: receptor and immune mechanisms.

We have previously shown that an acute administration of morphine (10 mg/kg, i.v.) decreases IgG, but not IgM, antibody levels to antigen administered before morphine. Further, decreases in IgG were blocked by previous administration of naltrexone, indicating that receptor binding is critical to the decreased antibody levels. These studies investigated potential receptor and immune mechanisms for these effects. To investigate potential receptor mechanisms, the stereoselectivity and location of receptor binding was determined. The results of these experiments suggest morphine must bind stereoselectively to central sites to decrease antibody levels after antigen administration. To investigate potential immune mechanisms for these changes, antibody secreting cells (ASC) for keyhole limpet hemocyanin-specific IgG and IgM were enumerated. Morphine decreased ASC for IgG but increased ASC for IgM. Two pathways for the genetic switch from IgM to IgG production were investigated. One pathway requires interferon-gamma to stimulate IgM-secreting cells to switch to IgG2a-secreting cells. Another pathway requires interleukin-4 to stimulate IgM-secreting cells to switch to IgG1- secreting cells. IgG1 and IgG2a levels were measured to determine if these pathways were differentially affected and only IgG2a levels were decreased. Further, these decreases were accompanied by decreased IFN-gamma levels but not by altered numbers of splenocytes. These data indicate that morphine may alter the ability of ASC to switch from IgM to IgG2a production, possibly by reducing the availability of IFN-gamma.

Stressed rats fail to expand the CD45RC+CD4+ (Th1-like) T cell subset in response to KLH: possible involvement of IFN-gamma.

Exposure to stressors effects various aspects of immune function, including the in vivo antibody response. We have previously reported that rats exposed to an acute session of inescapable tail shock (IS) show long-term reductions in anti-KLH (keyhole limpet hemocyanin) IgM and IgG. The mechanisms responsible for this suppression are currently unknown. Previous work has suggested changes in CD4+ T cells could be important. We report here that exposure to IS results in a reduction in Con A-stimulated IFN-gamma levels in mesenteric lymphocytes and splenocytes taken immediately after IS termination. In addition, IS exposure prevents the KLH-induced increase in the number of CD45RC+CD4+ T cells (Th1-like) in both the mesenteric lymph nodes and the spleen 4 days after immunization. The failure of KLH to expand the CD45RC+CD4+ subset could be due to the stress-induced reduction in IFN-gamma levels reported in cells taken at the time of immunization. Implications of these findings as a mechanism for the decrease in the in vivo antibody response previously reported is discussed.

Morphine-induced decreases in in vivo antibody responses.

Endogenous opioids have been shown to be released during acute stress and could play a role in immune modulation and activation of the hypothalamo-pituitary-adrenal axis. We investigated the ability of morphine sulfate to mimic stressor effects on decreases in in vivo antibody responses. Sprague-Dawley and Fischer 344 rats were given an intraperitoneal injection of an antigen, Keyhole limpet hemocyanin (KLH), followed by a single intravenous injection of either saline or varying doses of morphine sulfate. The corticosterone and anti-KLH IgG antibody responses to morphine were measured. A dose-dependent increase in corticosterone was observed. Significantly lower levels of anti-KLH IgG antibodies were observed in morphine-treated animals but these effects were strain and dose dependent. In Sprague-Dawley rats, 3 and 10 mg/kg doses of morphine decreased antibody levels while 1.5, 5, and 15 mg/kg did not change antibody responses. In Fischer 344 rats a dose of 5 mg/kg of morphine decreased antibody levels while 10 and 15 mg/kg did not change antibody responses. These results indicate that morphine can decrease antibody levels and that these decreases are not correlated with elevated levels of corticosterone. To determine if opioid binding is critical to these changes, animals received naltrexone prior to the administration of morphine. Naltrexone partially attenuated corticosterone levels, but completely blocked morphine-induced changes in immune function.

Anesthesia-induced modulation of in vivo antibody levels: a study of pentobarbital, chloral hydrate, methoxyflurane, halothane, and ketamine/xylazine.

The influence of anesthesia on long-term changes in in vivo antibody levels after antigen challenge was examined. Rats experienced a surgical plane of various anesthetics alone (anesthesia/intact) or in combination with laparatomy (anesthesia/laparatomy) and were given 1 or 3 wk to recover. Antigen, keyhole limpet hemocyanin, was then administered, and antibody levels specific to the antigen were measured during the next 14 days. Comparisons were made between anesthesia-treated animals and home cage controls. Pentobarbital and chloral hydrate produced decreases in in vivo antibody levels even 3 wk after exposure, whereas halothane, methoxyflurane, and ketamine/xylazine did not. Ketamine/xylazine produced moderate but not significant decreases in antibody levels when 1 wk intervened between exposure and antigen administration, but not when 3 wk intervened. Surgery did not produce larger changes in antibody levels than did anesthesia itself. These data suggest the possibility that some anesthetics, per se, may contribute to infection that may occur postoperatively.

Blockade of the hypothalamic-pituitary-adrenal response to stress by intraventricular injection of dexamethasone: a method for studying the stress-induced peripheral effects of glucocorticoids.

Interest in the mechanisms whereby stressors can influence behavior and physiological functioning has involved the use of a variety of methods to prevent the stress-induced release of glucocorticoids, an important and commonly studied stress hormone. We examined the effect of intracerebral ventricular dexamethasone (ICV DEX) on the stress-induced release of adrenocorticotropic hormone (ACTH), corticosterone, plasma epinephrine (E), and plasma norepinephrine (NE). Male Sprague-Dawley rats were stereotaxically implanted with third ventricle ICV cannulae, administered DEX or vehicle, and exposed to 100 1.6-mA tail shocks. Stress hormones were assessed from blood taken during and after the cessation the shock. We report an ICV DEX injection protocol (10 microgram given four times) that results in blocking the stress-induced release of ACTH and corticosterone, and attenuating the stress-induced release of plasma E and NE. We hypothesize that ICV DEX reduces hypothalamic corticotropin releasing hormone (CRH) synthesis and/or release. This method would be especially useful for those studying the effect of pituitary-adrenal hormones on steroid sensitive peripheral targets, such as the immune system.

Specific changes in lymphocyte subpopulations: a potential mechanism for stress-induced immunomodulation.

The mechanisms by which stressors alter immune function are not well understood. One hypothesis for stress-induced immunomodulation is that since immune responses require cooperation of different cell types, stress-induced shifts in cell populations might affect an organism's ability to mount an immune response. We sought to determine if inescapable shock (IS) could alter lymphocyte subpopulations and if so, whether this could be a mechanism for shock-induced immunomodulation. Our results suggest that IS produces changes in lymphocyte subpopulations and that these shifts could be responsible for modulation of in vivo antibody production. Exposure to IS resulted in an increase in the percent of CD4+ mesenteric lymphocytes and a decrease in the percent of CD8+ mesenteric lymphocytes when examined immediately after the cessation of IS. The stressor reduced antibody production to antigen processed at the altered mesenteric nodes, but did not alter antibody production to antigen processed at other sites. No measurable shifts were found in other compartments examined. The changes in CD4+ and CD8+ mesenteric lymphocytes resulted in an increased CD4+/CD8+ ratio that persisted for 1-24 h after stressor termination, becoming absent 48 h after IS termination. The stress-induced reduction in antibody production occurred only when antigen was given immediately prior to but not when antigen was given 48 h post stress. These findings suggest that the effects of a stressor could be specific to the manner in which the antigen enters the body, and that the stress-induced decrease in antibody production could be due to altered lymphocyte subpopulations as reflected by an increased CD4+/CD8+ ratio.