Implications of Salmonella-induced nitric oxide (NO) for host defense and vaccines: NO, an antimicrobial, antitumor, immunosuppressive and immunoregulatory molecule

Attenuated Salmonella induce immunosuppressive, microbicidal and tumoricidal macrophages in mice. All three effects are mediated by activated macrophages producing nitric oxide (NO). NO is induced by the innate immune response pathway involving IL-12, NK cells and IFN-gamma in response to infection. NO has beneficial and detrimental effects on the host.

Morphine inhibits mucosal antibody responses and TGF-beta mRNA in gut-associated lymphoid tissue following oral cholera toxin in mice

In this study, we investigated the effect of morphine on the mucosal immune system using fragment cultures of ileal segments, Peyer's patches (PPs), and mesenteric lymph nodes. Mice were implanted s.c. with a morphine slow release pellet. Control groups received a naltrexone slow release pellet, a placebo pellet, or both a morphine and a naltrexone pellet. After 48 h, mice were orally immunized with cholera toxin (CT) and were boosted orally 1 wk later. Animals were sacrificed 1 wk after the booster immunization, and PPs, mesenteric lymph nodes, and ileal segments were cultured in 24-well plates for 12 days. Morphine resulted in a highly significant inhibition of CT-specific IgA and IgG production in fragment culture supernatants of all three tissues compared with placebo. Naltrexone blocked the reduction in Ab levels induced by morphine, indicating that the effect is opioid receptor mediated. Morphine did not significantly alter total IgA levels in any of the tissue culture supernatants. Morphine also inhibited CT-specific IgA and IgG levels in serum. By flow cytometry, morphine did not alter the lymphoid cell composition in PPs compared with placebo. The effect of morphine on TGF-beta, IL-5, and IL-6 mRNA expression in PPs and ileal segments was determined following oral immunization with CT. Morphine significantly decreased TGF-beta mRNA compared with that in the placebo group, and naltrexone blocked this effect. These results indicate that morphine inhibits Ag-specific IgA responses in gut-associated lymphoid tissue at least partially through the inhibition of TGF-beta, a putative IgA switch factor, in the gastrointestinal tract.

Administration of mu-, kappa- or delta2-receptor agonists via osmotic minipumps suppresses murine splenic antibody responses

Previously, our laboratory has shown that morphine given by implantation of a 75-mg slow-release pellet for 48 h suppresses murine splenic antibody responses to sheep red blood cells (SRBCs) in a plaque-forming cell (PFC) assay. However, the use of slow-release pellets for such studies is limited, as these pellets are only available in fixed doses and similar pellets for kappa and delta agonists have not been developed. In the present study, we investigated the feasibility of administering opioids via Alzet osmotic minipumps to assess their immunomodulatory effects. Groups of mice received minipumps dispensing morphine sulfate, which has primary activity at the mu opioid receptor; U50,488H, which is a kappa-selective agonist; deltorphin II, which is a delta2-selective agonist; or DPDPE, which has greater selectivity for delta1 than delta, receptors. Morphine, U50,488H and deltorphin II were all immunosuppressive, with biphasic dose-response curves exhibiting maximal (approximately 50%) suppression of the PFC response at doses of 0.5 to 2 mg/kg/day 48 h after pump implantation. Further, immunosuppression by morphine sulfate, U50,488H or deltorphin II was blocked by simultaneous implantation of a minipump administering the opioid receptor-selective antagonists CTAP (1 mg/kg/day), nor-binaltorphimine (5 mg/kg/day), or naltriben (3 mg/kg/day), respectively. DPDPE was inactive at doses lower than 10 mg/kg/day. We conclude that osmotic minipumps are a practical and useful way of administering opioids to study their effects on the immune system, and give further evidence that immunosuppression induced in vivo by opioid agonists is mediated not only via mu, but also via kappa and delta2 opioid receptors.

Specific association of Type I c-Abl with Ran GTPase in lipopolysaccharide-mediated differentiation

Each of several isoforms of c-Abl may be involved in different biological functions. Type I c-Abl has been shown to be involved in LPS-induced differentiation and Type IV c-Abl, apoptosis. Ran has recently been shown to be involved in LPS endotoxin signal transduction. Here we show that Type I c-Abl associates with Ran. Formation of this complex is specific, as Ran did not associate with the highly homologous Type IV c-Abl isoform. In non-stimulated lymphoid B cells, Type I c-Abl tyrosine kinase is inactive, whereas Type IV kinase is active. Formation of Type I c-Abl/Ran complex and activation of Type I c-Abl kinase activity are LPS dose-dependent. This complex is detectable in B cells of endotoxin-sensitive inbred mice but absent in B cells of endotoxin-resistant mice. These findings therefore suggest that Type I c-Abl and Ran are important targets in lipopolysaccharide-induced biological responses of hematopoietic cells.

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.

Mu-opioid induction of monocyte chemoattractant protein-1, RANTES, and IFN-gamma-inducible protein-10 expression in human peripheral blood mononuclear cells

Strong evidence for the direct modulation of the immune system by opioids is well documented. Mu-opioids have been shown to alter the release of cytokines important for both host defense and the inflammatory response. Proinflammatory chemokines monocyte chemoattractant protein-1 (MCP-1), RANTES, and IFN-gamma-inducible protein-10 (IP-10) play crucial roles in cell-mediated immune responses, proinflammatory reactions, and viral infections. In this report, we show that [D-Ala(2),N:-Me-Phe(4),Gly-ol(5)]enkephalin (DAMGO), a mu-opioid-selective agonist, augments the expression in human PBMCs of MCP-1, RANTES, and IP-10 at both the mRNA and protein levels. Because of the proposed relationship between opioid abuse and HIV-1 infection, we also examined the impact of DAMGO on chemokine expression in HIV-infected cells. Our results show that DAMGO administration induces a significant increase in RANTES and IP-10 expression, while MCP-1 protein levels remain unaffected in PBMCs infected with the HIV-1 strain. In contrast, we show a dichotomous effect of DAMGO treatment on IP-10 protein levels expressed by T- and M-tropic HIV-infected PBMCs. The differential modulation of chemokine expression in T- and M-tropic HIV-1-infected PBMCs by opioids supports a detrimental role for opioids during HIV-1 infection. Modulation of chemokine expression may enhance trafficking of potential noninfected target cells to the site of active infection, thus directly contributing to HIV-1 replication and disease progression to AIDS.

Morphine enhances interleukin-12 and the production of other pro-inflammatory cytokines in mouse peritoneal macrophages

In this study we investigated the capacity of morphine to modulate expression of cytokines in peritoneal macrophages. Mice were implanted subcutaneously with a 75-mg morphine slow-release pellet, and 48 h later resident peritoneal macrophages were harvested. Control groups received placebo pellets, naltrexone pellets, or morphine plus naltrexone pellets. Adherent cells were stimulated with lipopolysaccharide (LPS: 10 microg/mL) plus interferon-gamma (IFN-gamma: 100 units/mL) to induce cytokine production. After 24 h RNA was extracted for analysis of cytokine mRNA levels by reverse transcriptase-polymerase chain reaction, or supernatants were collected after 48 h for determination of cytokine production by enzyme-linked immunosorbent assay (ELISA). Morphine enhanced mRNA expression of interleukin (IL)-12 p40 and tumor necrosis factor alpha (TNF-alpha) compared with controls, whereas IL-10 levels were unchanged by drug treatment. ELISA data showed that both IL-12 p40 and p70 were increased by morphine. The enhancement of IL-12 at both the mRNA and protein levels was antagonized by naltrexone, indicating that the modulation of this cytokine by morphine is via a classic opioid receptor. These results are particularly interesting in light of our previous observation that 48 h after morphine pellet implantation, the peritoneal cavity is colonized with gram-negative and other enteric bacteria. The enhancement of IL-12 by morphine might be related to morphine-induced sepsis.

Morphine attenuates leukocyte/endothelial interactions

Gram-negative sepsis and subsequent endotoxic shock after surgery remain problematic in the United States and throughout the world. While morphine is widely prescribed for postoperative trauma pain management, there are reports that morphine may compromise the immune system and contribute to postoperative sepsis. The current study tested the hypothesis that morphine attenuates leukocyte rolling and sticking in both arterioles and venules via nitric oxide production. Nude mice implanted with slow-release morphine pellets were used in this study. The dorsal skinfold chamber model for intravital fluorescence microscopy on awake mice was used. Leukocyte/endothelial interactions were evaluated after bolus injection of oxidized low density lipoprotein. Morphine was found to significantly attenuate leukocyte rolling and sticking in both the arterial and venular side of the microcirculation. This attenuation was reversed by simultaneous implantation of naloxone pellets. The mechanisms of this attenuation were further investigated by administration of the nitric oxide synthase inhibitors NG-nitro-l-arginine (NOLA) and aminoguanidine (AG) in drinking water. NOLA was found to significantly reverse this morphine-induced attenuation of leukocyte rolling and sticking in both arterioles and venules. However, AG did not have the same effect. The results indicate that morphine interferes with leukocyte/endothelial cell interactions via stimulation of nitric oxide production.

Morphine increases susceptibility to oral Salmonella typhimurium infection

This study examined the effect of morphine on oral infection with virulent Salmonella typhimurium. Animals were treated with a 75-mg slow-release morphine pellet followed by inoculation with salmonellae. Morphine markedly sensitized mice to oral infection, as assessed by survival, mean survival time, and colony culture. By 24 h after Salmonella inoculation, morphine-treated mice had a 105-fold difference in number of organisms in the Peyer's patches, compared with controls. The opioid antagonist naltrexone significantly blocked Salmonella colonization in Peyer's patches and reduced Salmonella burden in other organs, indicating that morphine acts at least in part via an opioid receptor-mediated pathway. The data show that morphine markedly potentiates Salmonella infection at the gastrointestinal portal of entry and enhances subsequent dissemination of Salmonella organisms. The results have implications for potentiating gastrointestinal opportunistic infections in intravenous drug abusers and in opioid-medicated postsurgical patients.

In vivo blockage of nitric oxide with aminoguanidine inhibits immunosuppression induced by an attenuated strain of Salmonella typhimurium, potentiates Salmonella infection, and inhibits macrophage and polymorphonuclear leukocyte influx into the spleen

Our laboratory has previously shown that after immunization with a strain of Salmonella typhimurium, SL3235, made avirulent by a blockage in the pathway of aromatic synthesis, murine splenocytes were profoundly suppressed in their capacity to mount an in vitro antibody plaque-forming cell (PFC) response to sheep erythrocytes. Evidence indicated that suppression was mediated by nitric oxide (NO), since the in vitro addition of NG-monomethyl-L-arginine blocked suppression. The present studies examined the effect of blocking NO production on Salmonella-induced immunosuppression by in vivo administration of aminoguanidine hemisulfate (AG). AG was administered to C3HeB/FeJ mice in their drinking water (2.5% solution) for 7 days prior to intraperitoneal inoculation with SL3235. AG treatment inhibited the increase in nitrate and nitrite levels in plasma and nitrite levels in the spleen seen in immunized mice. Importantly, AG treatment completely blocked suppression of the splenic PFC response and markedly attenuated the suppression of the response to concanavalin A in immunized mice, providing further evidence that Salmonella-induced immunosuppression is mediated by NO. AG treatment also alleviated the majority of the splenomegaly associated with SL3235 inoculation, which correlated with a blockage of influx of neutrophils and macrophages into spleens, as assessed by flow cytometry. AG treatment unexpectedly resulted in 90% mortality in mice injected with the highly attenuated vaccine strain of Salmonella, SL3235. Increased mortality in AG-treated mice correlated with inability to clear organisms from the spleen by day 15 postinoculation and with persistent bacteremia, compared with control mice. Collectively, these in vivo results underscore the dual biological consequences of NO production following Salmonella infection, with NO being necessary for host defense, but also having the potentially adverse effect of immunosuppression. A unifying hypothesis to explain how these seemingly paradoxical effects could both result from NO production is presented.

Salmonella typhimurium infection in mice induces nitric oxide-mediated immunosuppression through a natural killer cell-dependent pathway

Splenocytes isolated from C57BL/6J female mice 3 to 7 days after inoculation with an attenuated strain of Salmonella typhimurium produced high levels of nitric oxide (39 to 77 microM) and gamma interferon (IFN-gamma). Additionally, spleen cell cultures from Salmonella-inoculated mice were markedly suppressed in their ability to generate an in vitro plaque-forming cell (PFC) response to sheep erythrocytes. Depletion of natural killer (NK) cells from the immune splenocyte population markedly reduced nitric oxide production, prevented suppression of PFC responses, and completely abrogated IFN-gamma release. Treatment of NK cell-depleted immune cells with IFN-gamma restored nitric oxide production to levels comparable to those of intact immune cells and also restored the immunosuppression. These results suggest that NK cells regulate the induction of nitric oxide-mediated immunosuppression following infection with S. typhimurium through the production of IFN-gamma.

Characterization of kappa-opioid receptor transcripts expressed by T cells and macrophages

We have found that the immature T cell lines R1.1 and DPK and the macrophage lines P388D1 and WEHI-3 also express kappa-opioid receptor (KOR) mRNA. Characterization of the KOR transcripts in both brain tissue and these T cells has revealed both the normal full-length as well as a truncated form of the mRNA. Our results show that the truncated transcript lacks the second exon. Primary macrophages express this truncated form of the transcript in the absence of detectable levels of the full-length form. These results suggest a degree of heterogeneity in the expression of the opioid receptors which has not previously been reported.

Nitric oxide mediates immunosuppression induced by Listeria monocytogenes infection: quantitative studies

Our laboratory has shown that immunization of mice with an attenuated strain of Salmonella typhimuriuminduces profound suppression in the capacity of splenocytes to mount an in vitro antibody plaque-forming cell (PFC) response to sheep red blood cells (SRBC) and to proliferate in response to mitogens. In vitro addition of NG-monomethyl-L-arginine (NMMA), an inhibitor of nitric oxide (NO) synthase, to cell cultures from Salmonella-immunized mice completely blocked suppression of the PFC responses, implicating that NO is the suppressor factor. The present study quantified the role of nitric oxide in immunosuppression induced by Listeria monocytogenes, a gram positive intracellular pathogen of macrophages. Listeria infection resulted in suppression of the PFC assay at inoculating doses of greater than 6.5x10(3)colony forming units, with no suppression observed at lower doses. Suppression correlated with increased nitrite production. Addition of NMMA to spleen cell cultures taken from Listeria-infected mice completely blocked suppression of the PFC response, and returned nitrite production to baseline levels. In regard to Listeria-induced suppression of responses to the mitogen, Concanavalin A (Con A), the parameters were different from those observed for the PFC response. There was a direct correlation between the log10of the inoculating dose of Listeria and degree of immunosuppression, with suppression observed at doses as low as 1x10(3)cells. Addition of NMMA to the Con A-stimulated cultures resulted in reduced nitrite levels, but only partial restoration of the proliferative responses. Co-culture of splenocytes from Listeria inoculated mice with normal splenocytes in media with NMMA and reduced levels of L-arginine resulted in complete reversal of suppressed responses to Con A. Similar differences in ease of reversing suppression of the PFC response, as compared with responses to Con A, were previously noted using cells taken from Salmonella-infected mice. The present results show that a gram positive intracellular pathogen of macrophages, L. monocytogenes, induces immunosuppression in mouse spleen cells by a nitric oxide mediated mechanism that closely parallels that induced by the gram negative pathogen, S. typhimurium.

Involvement of C-Abl tyrosine kinase in lipopolysaccharide-induced macrophage activation

LPS endotoxin-induced macrophage activation is recognized to be important in both nonspecific immunity and endotoxin-induced sepsis when excessive macrophage stimulation occurs. In this study, we showed that reduction of c-Abl in macrophages prevented LPS-induced growth arrest, nitric oxide production and TNF-alpha secretion by ANA-1 macrophages. These cells continued to grow but later underwent apoptosis. Reduction of c-Abl in these cells led to reduced c-Abl kinase activity associated with Ran, which recently has been shown to be an LPS-responsive gene product. Our data suggest that c-Abl tyrosine kinase is one of the intermediates downstream of the initial signal transduction event related to activation of macrophages by LPS.

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.

Immunosuppression and nitric oxide production induced by parenteral live Salmonella vaccines do not correlate with protective capacity: a phoP::Tn10 mutant does not suppress but does protect

Previous work from our laboratory showed that an aroA mutant strain of S. typhimurium, SL3235, induces profound immunosuppression 7 days post-parenteral inoculation, and that the suppression is mediated by nitric oxide. Suppression was measured by the capacity of spleen cells to mount a primary in vitro plaque-forming cell response to sheep red blood cells in Mishell-Dutton cultures. In the present studies, the capacity of a panel of strains of attenuated Salmonella with various genetic lesions was tested. Most of the strains were S. typhimurium, but several were S. dublin. It was found that a variety of Salmonella strains induced suppression, demonstrating that suppressive capacity is not unique to SL3235 or to S. typhimurium. A strong correlation was obtained between the log10 of the microbial burden (cfu spleen-1) on the seventh day post-vaccine inoculation and the degree of immunosuppression. Strains that gave high spleen counts gave greater suppression. Microbial burden also correlated with the size of the spleen and the amount of nitrite produced by spleen-cell cultures, a measure of nitric oxide. Finally, the degree of immunosuppression was found to be linearly related to the log10 of the amount of nitrite produced. The capacity of the various strains of Salmonella to protect against challenge with virulent S. typhimurium, strain W118-2, was also tested. No correlation was found between suppressive and protective capacities of the various strains. Two strains suppressed, but did not protect. While most strains that protected grew or persisted in vivo, a phoP::Tn10 mutant of S. typhimurium did not grow or persist; this phoP mutant did not cause immunosuppression, but gave 100% protection against challenge with wild type S. typhimurium, suggesting that such mutants have advantageous properties as live vaccines.

Interleukin-12 is critical for induction of nitric oxide-mediated immunosuppression following vaccination of mice with attenuated Salmonella typhimurium

Studies from our laboratory have shown that infection of mice with an attenuated strain of Salmonella typhimurium causes a marked suppression in the capacity of splenocytes to generate an in vitro plaque-forming cell (PFC) response to sheep erythrocytes. The suppression has been shown to be mediated by mature, adherent macrophages (Mphis) and nonadherent, precursor Mphis. Nitric oxide has been identified as the suppressor factor. The present study investigated the role of interleukin-12 (IL-12) in the generation of nitric oxide-mediated immunosuppression in this model. Salmonella inoculation resulted in marked suppression of PFC responses and high levels of nitrite production. When mice were treated with anti-IL-12 prior to inoculation, nitrite levels in splenocyte cultures were reduced by 75% and the suppression of PFC responses was prevented. The nonadherent splenocyte fraction from Salmonella-inoculated mice, which contains precursor Mphis and is weakly immunosuppressive, was treated with IL-12 in vitro. IL-12 augmented the capacity of this fraction to suppress PFC responses by normal splenocytes in a coculture system. Additionally, IL-12 induced nitrite and gamma interferon (IFN-gamma) production in a dose-dependent manner. Treatment with anti-IFN-gamma blocked nitrite production and suppression, indicating that IFN-gamma is an important intermediary in the pathway of IL-12-induced immunosuppression. These results indicate that IL-12 is critical for the induction of nitric oxide-mediated immunosuppression following S. typhimurium inoculation and, through its ability to stimulate IFN-gamma production, can induce nitric oxide-producing suppressor Mphis.

Morphine alters macrophage and lymphocyte populations in the spleen and peritoneal cavity

We have previously shown that subcutaneous implantation of a 75 mg morphine pellet results in suppression of the ability of murine splenocytes to mount an antibody response to sheep red blood cells, due in part to a reduction of macrophage function. The present studies used flow cytometry to examine whether the decrement in macrophage function in the spleens of morphine-treated mice results from a reduction in macrophage numbers. Parallel analysis was carried out on non-elicited peritoneal cells. In the spleen, morphine resulted in a reduction in the relative proportion of macrophages and B-cells, with a concomitant increase in the proportion of T-cells. Alteration in the ratio of CD4+ to CD8+ T-cells was not observed. In contrast, in the peritoneal cavity, morphine increased the number of macrophages and reduced the number of B-cells. Naltrexone blocked all of the changes in cellular composition. These results support the conclusion that an important mechanism in the immunosuppression seen in the spleens of mice implanted with morphine pellets is a differential reduction in the number of macrophages and B-cells as compared with T-cells. Further, these studies show that subsets of cells of the immune system are differentially affected by morphine in different anatomical compartments.

Morphine induces sepsis in mice

Gram-negative sepsis and subsequent endotoxic shock remain major health problems in the United States. The present study examined the role of morphine in inducing sepsis. Mice administered morphine by the subcutaneous implantation of a slow-release pellet developed colonization of the liver, spleen, and peritoneal cavity with gram-negative and other enteric bacteria. In addition, the mice became hypersusceptible to sublethal endotoxin challenge. The effects were blocked by the simultaneous implantation of a pellet containing the opioid antagonist naltrexone. These findings show that morphine pellet implantation in mice results in the escape of gram-negative organisms from the gastrointestinal tract, leading to the hypothesis that morphine used postoperatively or chronically for analgesia may serve as a cofactor in the precipitation of sepsis and shock. In addition, morphine-induced sepsis may provide a physiologically relevant model of gram-negative sepsis and endotoxic shock.

Inhibition of T cell superantigen responses following treatment with the kappa-opioid agonist U50,488H

Previous work in our laboratory has shown that cytokine production by primary murine macrophages, and macrophage cell lines, is inhibited following treatment with the kappa-opioid agonist U50,488H. Furthermore, we have found that the participation of both accessory cells and T cells in an antibody response is suppressed by this compound. We have utilized the superantigen staphylococcal enterotoxin B (SEB) to further examine the effects of U50,488H on accessory and T cell function. The results showed that the proliferative response of lymph node T cells to SEB presented by activated macrophages was significantly inhibited by the kappa-opioid agonist at concentrations as low as 100 nM. However, suppression of the T cell response to SEB presented by resting macrophages required 100 times the concentration of U50,488H. On the other hand, the production of IL-2 in response to lymph node T cell stimulation with SEB was not altered by the opioid treatment. Additional experiments utilizing the opiate antagonist naloxone and the kappa-selective antagonist nor-binaltorphimine (norBNI) were performed in order to further characterize the opioid receptor involved in the suppressive activity of U50,488H. Results showed that both naloxone and norBNI were able to block the inhibitory activity of U50,488H. Further analysis showed that the proliferative response of thymic T cells was more sensitive to the effects of U50,488H, and the response with both activated and resting macrophages was suppressed. In addition, the production of IL-2 by the thymic T cells was also inhibited by the opioid treatment. The mechanism of suppression of superantigen-induced T cell responses is discussed.

Attenuated Salmonella vaccine-induced suppression of murine spleen cell responses to mitogen is mediated by macrophage nitric oxide: quantitative aspects

Previous reports from our laboratory have shown that 7 days after infection of C3HeB/FeJ mice with an attenuated strain of Salmonella typhimurium, there is profound suppression of responses to B- and T-cell mitogens and suppression of the capacity of spleen cells to mount a primary, in vitro plaque-forming-cell (PFC) response to sheep erythrocytes. Inhibition of the PFC response was shown to be mediated by nitric oxide (NO), as NG-monomethyl-L-arginine (NMMA) gave complete reversal of suppression. The experiments reported here examined the role of NO in suppression of the response to the mitogen concanavalin A (ConA). In contrast to the PFC system, it was found that addition of NMMA to ConA-stimulated immune spleen cells resulted in less than 20% reversal of suppression. However, addition to NMMA resulted in a 50% reversal of suppression in cocultures of immune and normal spleen cells at a ratio of 1:4. A complete restoration of ConA-induced responses was achieved in cocultures incubated in medium containing a reduced concentration of L-arginine plus 1.25 mM NMMA. Investigation of why NMMA alone was not 100% effective in reversing suppression showed that addition of ConA significantly augmented production of nitrite and gamma interferon (IFN-gamma) in cocultures containing immune cells. Addition of anti-IFN-gamma reduced nitrite levels in the cultures, although results with the combination of anti-IFN-gamma and NMMA were not significantly better than results with NMMA alone. These findings suggest that suppression in cultures stimulated with ConA is difficult to reverse completely with NMMA alone because of an overproduction of NO, which can be offset by either reducing the L-arginine concentration or blocking IFN-gamma. The quantitative relationship between nitrite levels and suppression in cocultures was examined. It was found that suppression did not correlate directly with the nitrite concentration but rather with the log10 of the nitrite concentration. Nitrite levels above 15 microM gave almost complete suppression, and levels between 1 and 10 microM gave a wide range of suppression. These results strongly support NO as the suppressor factor in Salmonella-induced immunosuppression of responses to ConA and, by inference, suppression of responses to mitogens induced by other microbes. The results show that involvement of NO cannot always be demonstrated by simple addition of NMMA to suppressed mitogen-stimulated spleen cell cultures.

Inhibition of primary murine macrophage cytokine production in vitro following treatment with the kappa-opioid agonist U50,488H

Previous work in our laboratory has shown that both mu- and kappa-opioid agonists exhibit immunosuppressive activity for antibody responses in vitro. Our earlier work has suggested that both accessory cells and T cells may be altered following treatment with the kappa-opioid agonist U50,488H. We intend to further determine the identity of the immune cell population(s) which are affected by opioid treatment, and to determine the nature of the opioid receptor type expressed on these cells. In this study, non- elicited peritoneal macrophages were treated simultaneously with the kappa-agonist U50,488H and lipopolysaccharide (LPS), and the levels of the cytokines interleukin (IL)-1, IL-6 and tumor necrosis factor (TNF)-alpha were determined. The results show that U50,488H had a suppressive effect on the production of TNF-alpha and IL-1 at concentrations as low as 1 nM, while IL-6 was suppressed at concentrations as low as 10 nM. Additional experiments utilizing the opiate antagonist naloxone and the kappa-selective antagonist norbinaltorphimine (norBNI) were performed in order to further characterize the opioid receptor involved in the cytokine suppression produced by treatment with U50,488H. Results showed that naloxone was able to partially block U50,488H suppression while norBNI was able to completely reverse the suppression of IL-6 production. These results suggest that macrophage/monocyte function is significantly modulated following activation of the kappa-opioid receptor.

Mouse strain differences in immunosuppression by opioids in vitro

An in vitro assay was used to compare the effect of opioids on antibody production by splenocytes from C3HeB/FeJ, C57BL/6J, C57BL/6ByJ and B6C3F1/J mice immunized with sheep red blood cells (SRBC). Spleen cells were removed from mice that had been injected 2 wk prior with SRBC. These mice received no opioids in vivo. Dissociated spleen cells taken from each of the mouse strains were exposed to morphine with or without naloxone, or to U50,488H with or without norbinaltorphimine (nor-BNI), for 5 days in a Mishell-Dutton culture, with added SRBC as antigen. Immune responsiveness was assessed by the number of plaque-forming cells (PFC) per culture. The results showed a profound difference in the effects of the opioids on the spleen cells of the four mouse strains. Spleen cells of C3HeB/FeJ mice were suppressed approximately 50% in the number of PFC both by morphine (10(-5) to 10(-8) M) and by U50,488H (10(-5) to 10(-11) M). Suppression was blocked by pretreatment with naloxone or norbinaltorphimine, respectively. In contrast, spleen cells taken from C57BL/6J mice were not suppressed by either opioid, at doses ranging from 10(-5) to 10(-11) M. Spleen cells of B6C3F1/J mice were suppressed by U50,488H, but not morphine. Cells of C57BL/6ByJ mice gave inconsistent results in experiments measuring suppression by morphine, and U50,488H. Overall, these studies confirm our previous work showing that opioids directly affect the function of cells of the immune system via classical opioid receptors. In addition, the results show that mouse strain is a major variable in evaluating the immunomodulatory effects of opioids.

Sequence of kappa-opioid receptor cDNA in the R1.1 thymoma cell line

To our knowledge, this is the first demonstration of kappa-opioid receptor mRNA in cells of the immune system. While the presence of opioid receptors on cells of the immune system has been controversial, cell-binding analysis has indicated that the kappa-opioid receptor is expressed by the immature T cell line R1.1. We have developed a reverse transcriptase-polymerase chain reaction protocol to amplify the mRNA extracted from R1.1 cells with primers derived from the cDNA sequence of the mouse kappa-opioid receptor. Nucleotide sequences of the amplified products were examined and two populations of cDNA were detected which differ in the 5' region upstream of the ATG start codon. Comparison of these sequences to the previously published kappa-opioid receptor cDNA sequence suggests the presence of an intron-exon junction in the 5' non-coding region.

Inhibition of interleukin-1 and tumor necrosis factor-alpha synthesis following treatment of macrophages with the kappa opioid agonist U50, 488H

Previous reports from this laboratory, and others, have shown that exogenous mu and kappa opioids modulate both cellular and humoral immune responses. Our earlier work has suggested that accessory cells may serve as a target for the direct effects of kappa opioid compounds. In the present study, the function of the macrophage cell line P388D1 was modulated by the kappa-selective opioid agoinst U50,488H (trans-3,4-dichloro-N-methyl-N-[7-(1- pyrrolidinyl)cyclohexyl]benzene-acetamide methanesulfonate). Lipopolysaccharide-induced interleukin (IL)-1 and tumor necrosis factor-alpha production were inhibited after the administration of nanomolar concentrations of U50,488H. Furthermore, inhibition of IL-1 produced by the P388D1 cell line was reversed by both the classical opioid antagonist naloxone and by the kappa opioid receptor antagonist norbinaltorphimine. Examination of IL-1 mRNA levels in P388D1 by northern blot analysis showed that the inhibition mediated by U50, 488H apparently occurred at the level of transcription. On the other hand, U50,488H failed to modulate the production of IL-6 by this macrophage-like cell line. In addition, U50,488H failed to modulate the production of either IL-1 or tumor necrosis factor-alpha from the macrophage-like cell line RAW 264.7, an indication that subpopulations of macrophages exist with different sensitivities to opioids. These results are consistent with a growing body of data which suggests that a component of the inhibition mediated by opioid compounds involves a reduction in the production of cytokines.

Immunotherapy of a plasmacytoma with attenuated salmonella

An attenuated strain of Salmonella typhimurium, SL3235, developed as a prototypic typhoid vaccine, is shown to retard growth of a murine plasmacytoma, TEPC-183, and to prolong survival of tumor-bearing mice. Live salmonella, but not acetone-killed organisms, had antitumor activity. The immunotherapeutic effect was demonstrable when the tumor was injected intralesionally or intraperitoneally. Increased survival, longer mean time to death, and retardation of tumor growth were found when the salmonella were given intralesionally as late as the sixth day post-tumor injection. Timing of salmonella inoculation, as well as the salmonella dose, had an effect on treatment efficacy. Injection of salmonella intraperitoneally exerted a strong antitumor effect when given as late as the third day post-tumor inoculation. The highest dose (2 x 10(6)) of salmonella was less effective than doses 10- or 100-fold lower. TEPC-183 plasmacytoma is rapidly growing and highly immunosuppressive, so the ability of the salmonella to exert therapeutic activity against it is a measure of the potency of the vaccine. These observations are of interest, as they show that a genetically engineered, avirulent strain of Salmonella has immunotherapeutic properties similar to those of BCG and other biological response modifiers, and might have clinical potential as an antitumor agent.

Decreases in macrophage mediated antitumor activity with aging

We have demonstrated that immunotherapy of young (6-10 weeks old), and aged, (greater than 24 months old), tumor bearing mice with biological response modifiers enhanced survival and inhibited tumor growth, while treatment of aged mice had little or no effect. We hypothesized that the antitumor activity in young mice was principally mediated by activated macrophages (M phi) and predicted that the change in aged mice was caused by an intrinsic M phi defect which develops with advancing age. To directly test our hypothesis, we examined the antitumor activity of resident peritoneal M phi, purified and activated in vitro with IFN gamma plus LPS. Paralleling the results seen in vivo, M phi from aged mice exhibited reduced antitumor activity in comparison with M phi from younger mice. Moreover, there was reduced capacity of in vitro activated M phi from aged mice to produce TNF, IL-1 and nitric oxide, which are critical monokines and effector molecules that have been established to either directly inhibit tumor growth or cause tumor cell destruction. These studies establish that peritoneal M phi from aged mice have an intrinsic defect which prevents them from fully expressing their antitumor potential.

Detection of kappa-opioid receptor mRNA in immature T cells

The R1.1 cell line has been shown to express kappa-opioid receptors on the cell surface. Our analysis shows that the R1.1 cell line exhibits a CD4NEG CD8NEG CD3LOW CD25LOW cell surface phenotype, characteristic of thymocytes in one of the early stages of differentiation. We have developed reverse transcriptase polymerase chain reaction (RT-PCR) conditions that permit the detection of mRNA coding for the kappa-receptor. Using cell fractionation techniques we have isolated CD4NEG CD8NEG thymocytes, and analysis by RT-PCR shows that these primary immature thymocytes also express the kappa-opioid receptor. We hypothesize that the expression of kappa-opioid receptor may be a marker which is characteristic of immature T development.

Macrophage nitric oxide mediates immunosuppression in infectious inflammation

A vaccine strain of live, attenuated Salmonella typhimurium induces profound immunosuppression in inoculated mice 7 days after injection. Immunosuppression to mitogens and inability to mount plaque-forming responses to sheep red blood cells occurs in spite of many parameters of upregulated macrophage function and protection against challenge with virulent Salmonella. Studies show that macrophage nitric oxide mediates the immunosuppression and presumably also the early-onset protective capacity of the vaccine. A model of "bystander lymphocyte autotoxicity" is presented to explain the mechanism of immunosuppression. The model proposes that Salmonella-activated macrophages generate nitric oxide which inactivates lymphocytes in the vicinity, so they become dysfunctional. Inhibition of nitric oxide by NG-monomethyl-L-arginine reverses immunosuppression. Evidence is presented that supports a relationship between the microbial burden in the spleen, the degree of nitric oxide produced, and the extent of immunosuppression. It is proposed that this model of microbial immunosuppression mediated by nitric oxide is generalizable for understanding immunosuppression and loss of delayed-type hypersensitivity induced by other microbes, such as Mycobacteria and measles virus. The model could account for anergy during mycobacterial infections, particularly when the burden of acid-fast bacilli is high, as well as loss of skin test reactivity to tuberculin during measles infection.

Both T cells and macrophages are targets of kappa-opioid-induced immunosuppression

We have previously shown that antibody responses are inhibited following administration of kappa-opioid agonists. We found that the inhibition was blocked by either naloxone or the kappa-selective antagonist norbinaltorphimine. This inhibitory activity is apparent after short-term treatment with the kappa-opioid agonist. In an attempt to identify the cell populations which serve as the target for this immunosuppressive effect, we have carried out cell fractionation analyses to generate isolated T cells and macrophages. Using multiple cell fractionation methods, we have determined that short-term treatment of either T cells or macrophages with the kappa-opioid agonist U50,488H results in significant inhibition of in vitro antibody responses. We also find that the inhibition of both T cell and macrophage activity can be blocked by naloxone. These studies demonstrate that resting T cells and macrophages express kappa-opioid receptors and exhibit significant opioid responsiveness prior to activation by antigen.

Herpes simplex virus type 1 replication and IL-1 beta gene expression in mouse peritoneal macrophages activated in vivo by an attenuated Salmonella typhimurium vaccine or Corynebacterium parvum

Activated macrophages (M phi) from mice given Salmonella typhimurium or Corynebacterium parvum were compared with resident peritoneal macrophages at the molecular level for permissiveness for herpes simplex virus type 1 (HSV-1) replication and for expression of interleukin-1 beta (IL-1 beta). Peritoneal macrophages were harvested from mice injected 7 days previously with live, avirulent S. typhimurium (Sal-PM phi) or heat-killed C. parvum (CP-PM phi) and infected with HSV-1 in vitro. Both Sal-PM phi and CP-PM phi were activated as evidenced by characteristic changes in an ectoenzyme, by increased permissiveness for infectious virus production and viral cytopathic effect, and by induction of IL-1 beta mRNA. Analysis at the molecular level revealed that both types of activated M phi demonstrated increased patterns of HSV-1 immediate-early gene expression and viral DNA replication as compared with resident cells. A novel finding was that viral infection reduced IL-1 beta mRNA in both types of activated M beta. This observation has implications for the efficacy of Salmonella vaccines given in proximity to HSV-1 infection and for potential deleterious effects of HSV-1 infection in immunosuppressed patients receiving immunotherapy.

Suppression of peritoneal macrophage phagocytosis of Candida albicans by opioids

Receptor-selective opioid agonists have been found to suppress the capacity of macrophages to ingest opsonized sheep erythrocytes. In an effort to characterize the immunomodulatory activity of opioids further, experiments were done to examine the uptake of Candida albicans by opioid-treated murine peritoneal macrophages. It was found that treatment with morphine and selective mu, i.e., DAMGO, delta, i.e., DPDPE, and kappa, i.e., trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]benzene-acetamide methanesulfonate, receptor agonists resulted a concentration-dependent suppression of both the percentage of phagocytic cells and the average number of ingested yeasts. Antagonists selective for mu, i.e., H-D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2, delta, i.e., naltrindole, and kappa, i.e., norbinaltorphimine, opioid receptors completely blocked the respective receptor-selective agonist-induced suppression. These results suggest that the mu, delta and kappa opioid receptors can modulate macrophage function.

Cytokine reversal of morphine-induced suppression of the antibody response

Female C3HeB/FeJ mice implanted with a morphine pellet exhibit a decreased primary antibody response in vitro as measured by the plaque-forming cell (PFC) assay. Suppression was detected at 24 hr following pellet implantation, was maximal at 48 hr and returned to normal by 120 hr. Splenocytes from control mice cocultured with splenocytes from morphine-treated mice (3:1 ratio) did not show a significant suppression, suggesting that morphine is not inducing the production of suppressor cells and/or factors. However, cells from morphine-treated mice cocultured with control cells (3:1) had a restored response. Further coculture experiments demonstrated that addition of adherent cells, but not nonadherent cells, restored the antibody response, suggesting that the macrophages from morphine-treated mice were deficient or defective. In vitro addition of interleukin (IL)-6, IL-1 beta or interferon-gamma (0.5-50 U/ml) attenuated the suppression of the PFC response in cells from morphine-treated mice, whereas higher doses (100 U/ml) restored completely the PFC response to control levels. Addition of IL-2, IL-4 or IL-5 to cultures from morphine-treated mice had little effect. Thus, morphine appears to cause immune suppression by reducing macrophage numbers or by interfering with the production or release of specific cytokines which are needed for a normal antibody response. Collectively, these data suggest that the macrophage is a key cellular target for the suppressive effects of morphine on the antibody response.

Opioids, receptors, and immunity

The results achieved by those seeking to determine whether opioids and other drugs of abuse can affect immunity are quite astonishing given the short period of time that research has focused on this area. Despite the fact that there is no longer any question that opioids produce a variety of effects on the immune system, the extent and significance of these changes in the drug-abusing population remains to be determined. Whether or not the findings in mice and in in vitro preparations can be extrapolated to man is not yet known. Of major significance is the question of whether the endogenous opioid system is involved in immunoregulation. Given the multitude of drugs taken by drug abusers and the varying patterns of drug administration, the significance of the findings in the literature is still an open question. However, it is only by continuing studies such as those discussed at this meeting that we will find the answers.

Immunosuppressive effects of morphine on immune responses in mice

Implantation of a 75-mg morphine sulfate pellet subcutaneously into mice of different strains and sexes caused profound immunosuppression of their spleen cell primary in vitro antibody responses to sheep red blood cells. No sex differences were observed. In mice of the C3H lineage, naltrexone blocked the immunosuppression. In mice in the C57BL/6J lineage, naltrexone was ineffective in blocking the effects of morphine and was itself suppressive. In beige C57BL/6J bgJ/bgJ mice, placebo pellets were also suppressive. The mechanism of the morphine-induced immunosuppression was investigated in C3HeB/FeJ mice. Addition of normal splenic macrophages to in vitro cultures restored immune responses, as did IL-1, IL-6 and IFN-gamma, suggesting that morphine-induced immunosuppression is due to a deficit in macrophage function. Morphine pellet implantation induced splenic atrophy. Whether suppression is attributable to decreased macrophage numbers or to decreased functional capacity of individual macrophages is currently under investigation.

Morphine treatment in vitro or in vivo decreases phagocytic functions of murine macrophages

Studies were performed to compare in vitro and in vivo effects of morphine on the phagocytic function of murine peritoneal macrophages. Macrophage monolayers were incubated with Candida albicans for 30 min in the absence of autologous serum. Morphine added in vitro was found to decrease both the phagocytic activity (percent of phagocytic cells) and the phagocytic index (average number of ingested yeasts per cell) in a concentration-dependent manner, with maximal effects of 26% and 41%, respectively, at 10(-6) M. When morphine was administered in vivo via an implanted 75-mg pellet, there was a 22% decrease in phagocytic activity and a 40% decrease in the phagocytic index. Naltrexone completely blocked the effects of morphine both in vitro and in vivo. The results suggest that morphine is capable of interacting directly with opioid receptors on macrophages, resulting in a decrease in phagocytic function.

Effects of in vivo morphine treatment on antibody responses in C57BL/6 bgJ/bgJ (beige) mice

C57BL/6J bgJ/bgJ (beige) mice are less sensitive than other strains to the analgesic effects of morphine, although they have normal numbers of mu receptors. In the present study, beige mice and their normal littermates (beige+) were treated in vivo with morphine or the opioid antagonist, naltrexone and their primary in vitro antibody responses were assessed. Morphine treatment caused splenic atrophy and suppressed the primary in vitro antibody response in beige and beige+ mice. However, these effects were not blocked by naltrexone co-treatment. In these mouse strains, naltrexone decreased spleen size and antibody responses by itself, which may mask its ability to antagonize morphine. In beige mice, placebo pellet implantation suppressed the primary in vitro antibody response. Morphine did not cause a further suppression of the antibody response in beige mice compared to placebo. Because of this anomalous response to placebo treatment, the immunosuppressive effects of morphine on the antibody response/10(7) cells can not be attributed to a specific drug effect in this strain. However, when antibody responses were expressed on a per spleen basis, the overall capacity to respond to antigenic challenge was suppressed by morphine treatment.

Immunosuppression induced by nitric oxide and its inhibition by interleukin-4

Mice immunized with attenuated Salmonella typhimurium, strain SL3235, while protected against virulent challenge, are unable to mount in vivo and in vitro antibody responses to non-Salmonella antigens, such as tetanus toxoid and sheep red blood cells, and exhibit profoundly suppressed responses to B and T cell mitogens. Suppression of antibody responses is mediated by macrophage (M phi)-released soluble factors, and is completely reversed by treatment with interleukin (IL)-4. The present report identifies the suppressor factor as nitric oxide (NO), and provides evidence for a mechanism by which IL-4 abrogates suppression. Suppressed antibody responses correlated with high levels of NO secretion by splenocytes of SL3235-immunized mice. NO production was observed only in cultures consisting of the adherent cell fraction of immune splenocytes. Further, immunosuppression was reversed by NG-monomethyl-L-arginine (NMLA), a competitive inhibitor of NO synthesis, and was completely blocked by the addition of excess L-arginine. Treatment with IL-4, or anti-interferon (IFN)-gamma monoclonal antibody (mAb), also abrogated suppression. Optimal reversal of suppression was observed only when NMLA, IL-4, or anti-IFN-gamma mAb, was added at day 0 of the 5-day plaque-forming cell assay. Treatment with either IL-4 or anti-IFN-gamma mAb also lead to a sharp inhibition of NO production by immune spleen cells. Moreover, the addition of IL-4 to splenic adherent M phi inhibited their ability to generate NO. Our data characterize an immunoregulatory pathway, involving IFN-gamma and NO, by which M phi mediate immunosuppression and identify IL-4 as a potent inhibitor of this pathway.

Immunosuppression induced by attenuated Salmonella: effect of LPS responsiveness on development of suppression

A live, avirulent strain of Salmonella typhimurium, SL3235, was previously shown to afford protection against virulent Salmonella challenge in three mouse strains of the C3H lineage, C3H/HeJ, C3HeB/FeJ, and C3H/HeNCrlBR, which differ in their innate susceptibility to Salmonella infection, as well as in their responsiveness to lipopolysaccharide (LPS). Concurrent with protection, however, SL3235 was found to induce greater than 90% reduction in proliferative responses of splenocytes from immunized mice to a panel of B and T cell mitogens. Suppression appeared to be independent of susceptibility to Salmonella infection, since the mitogenic responses of hypersusceptible C3H/HeJ and C3HeB/FeJ, as well as resistant C3H/HeNCrlBR mice, were suppressed. The suppressor cell population in immunized C3HeB/FeJ mice was recently shown to be of monocytic lineage. Using transwell plates, co-culture studies indicated that suppression was mediated by soluble factors. In the present study, the effect of LPS responsiveness on susceptibility to SL3235-induced suppression was evaluated in C3H mice by studying their ability to mount plaque-forming cell (PFC) responses to sheep red blood cells (SRBC) and in vivo antibody responses to tetanus toxoid. Comparison of PFC responses as a function of SL3235 dose in C3HeB/FeJ and C3H/HeJ mice, revealed that the latter strain was markedly more resistant to the development of suppression, as evidenced by the significantly higher (10-35-fold) SL3235 doses needed to achieve comparable suppression to those seen in C3HeB/FeJ mice. In contrast to C3HeB/FeJ mice, suppression in C3H/HeJ mice required direct cell-cell contact. In both mouse strains, suppression was alleviated by pre-treatment of immune splenocytes with either mitomycin C or x-irradiation, indicating that actively proliferating cells are required for suppressor function. Resistance of C3H/HeJ mice to SL3235-induced suppression was not due to a lesser bacterial load in vivo, since a higher number of SL3235 organisms were seen in C3H/HeJ spleens compared to C3HeB/FeJ mice. Rather, resistance of C3H/HeJ mice correlated with their reduced ability to recruit macrophages and other inflammatory cells into the spleen, as evidenced by the significantly smaller degree of splenomegaly induced in these mice following immunization with SL3235.

Natural killer cells mediate protection induced by a Salmonella aroA mutant

We have previously shown that an avirulent strain of Salmonella typhimurium, SL3235, blocked in aromatic synthesis, confers high levels of resistance to challenge with virulent Salmonella as early as 3 days postvaccination. In the present studies, it was found that immunization with SL3235 resulted in high levels of natural killer (NK) cell activity in the spleens and peritoneal cavities of C3H/HeJ mice, as measured by cytotoxicity against YAC-1 targets. NK cell activity was at its maximum 2 to 4 days after immunization and was ablated by in vivo or in vitro treatment with anti-asialo GM1. In vivo treatment with anti-asialo GM1 during the first week after immunization with SL3235 depleted NK cell activity and markedly increased mortality in mice challenged with a virulent Salmonella strain. These results are compatible with a role for NK cells as one important component in the resistance against virulent Salmonella infection induced by a live, attenuated vaccine.

Differential effects of morphine and naltrexone on the antibody response in various mouse strains

Morphine treatment has been shown to suppress several immunologic parameters. In this study, we examined the effects of morphine pellet implantation in vivo on the primary antibody response measured in vitro in various mouse strains. Effects of mouse strain and sex on morphine-induced suppression of the plaque-forming cell response, as well as spleen weight and mortality were determined. Morphine suppressed the primary antibody response in C3HeB/FeJ, C3H/HeJ and C57Bl/6 mice, while Balb/cByJ and the mu-receptor-deficient strain CxBk/ByJ mice were not affected. There was no difference in the response to morphine between male and female C3HeB/FeJ mice. Naltrexone reversed the morphine-induced suppression in the C3H strains, but not in C57Bl/6 mice. In addition, naltrexone caused significant mortality in Balb/cByJ mice. Spleen weight was decreased by morphine treatment in all the strains, but only the C3H strains were sensitive to the lethal effects of morphine. Thus, immune suppression did not correlate with splenic atrophy or mortality. The strain differences in response to chronic morphine and naltrexone treatment suggest that morphine may be acting through both opioid and non-classical opioid (e.g., not blocked by naltrexone) mechanisms.

Effect of herpes simplex virus type 1 infection on cytokine gene expression in activated murine peritoneal macrophages

The intrinsic resistance to herpes simplex virus type 1 (HSV-1) of murine peritoneal macrophages (PM phi) obtained after in vivo infection of different stimuli has been investigated and shown to vary depending on the state of M phi activation. Activation of M phi by C. parvum (CP-M phi) or by an avirulent strain of S. typhimurium (Sal-M phi) increased the permissiveness of M phi to HSV-1 infection as evidenced by increased HSV-1 immediate early (IE) gene expression, synthesis of IE proteins, and the degree of cytopathic effect. HSV-1 infection was also found to sharply reduce the level of IL-1-beta mRNA in CP-M phi) and Sal-M phi, and the level of IL-3 mRNA in infected Sal-M phi, as measured by northern blot hybridization. Barely detectable levels of IL-beta mRNA were found in Sal-M phi after infection with HSV-1 when the polymerase chain reaction (PCR) assay was used to confirm the reduction of IL-1-beta mRNA. These data suggest that HSV-1 infection can modulate gene expression of some cytokines in the activated M phi.