Inducible cyclooxygenase released prostaglandin mediates immunosuppression in acute phase of experimental Trypanosoma cruzi infection

We investigated the possible role of prostaglandins produced by COX-2 in the immunosuppression observed during Trypanosoma cruzi infection. Con-A-stimulated splenocytes isolated from mice on days 5, 10, and 15 of infection released large amounts of PGE2 and this release was inhibited by the treatment of animals with sodium salicylate or meloxicam. The treatment of the animals with these drugs enhanced the release of IL-2 by splenocytes from T. cruzi-infected animals and significantly reduced the blood parasitemia and delayed the mortality of the infected mice. Furthermore, the release of TNF-alpha, IFN-gamma, IL-4, and IL-10 by Con-A-stimulated splenocytes obtained from infected mice on days 5, 10, and 15 of the infection was significantly inhibited by treatment of the animals with salicylate or meloxicam. In conclusion, the results suggest that the prostaglandins produced mainly by COX-2 mediate the immunosuppression observed in the acute phase of T. cruzi infection.     

Prostaglandins mediate suppression of lymphocyte proliferation and cytokine synthesis in acute Trypanosoma cruzi infection

Suppression of host lymphoproliferative responses to mitogens and Ag is characteristically seen during acute infection with the protozoan parasite Trypanosoma cruzi. We investigated the reciprocal regulation of prostaglandins (PG), TNF-alpha, and nitric oxide (NO) production and their effects on cytokine production and lymphoproliferative responses to parasite Ag and to Con A by spleen cells (SC) from T.-cruzi-infected mice. Large amounts of PGE2, TNF-alpha, and NO were produced during infection. TNF-alpha stimulated PG and NO synthesis, while both mediators inhibited TNF-alpha synthesis. Blocking PG also reduced NO synthesis indicating that PG stimulate NO production. Treatment with indomethacin or NMLA stimulated lymphoproliferation on days 6 and 22 of infection; on day 14, when suppression of proliferation and NO production was maximal, combined inhibition of NO and PG production restored parasite Ag specific and Con A proliferative responses. Blocking PG or NO production increased IL-2, IFN-gamma, and TNF-alpha, but not IL-12 production by SC; IL-10 levels were not reduced. Indomethacin-treated infected mice had higher mortality compared to untreated infected animals. The data indicate that PG, together with NO and TNF-alpha, participate in a complex circuit that controls lymphoproliferative and cytokine responses in T. cruzi infection.     

The role of interleukin 6 in interferon-gamma production in thermally injured mice

Following traumatic injury, patients suffer from compromised immunity increasing their susceptibility to infection. Previous studies from this laboratory demonstrated that female BALB/c mice subjected to a 15% total body surface area (TBSA) scald injury exhibit a decrease in cell-mediated immunity 10 days post-burn. Studies described herein revealed that concanavalin A (Con A; 2 microg/ml)-stimulated splenocytes from sham treated animals produced 3557+/-853 pg/ml of IFN-gamma while splenocytes from burn injured animals released two-fold more cytokine (P<0.05). To determine whether leukocyte production of IFN-gamma was under the influence of macrophages, splenic macrophage supernatants generated from burned animals were incubated with splenic lymphocytes from sham and burn animals. The amount of IFN-gamma released by lymphocytes from sham animals increased when cultured with macrophages from burned mice (P<0.05). This suggests that the increase in IFN-gamma production by unfractionated splenocytes in burned mice relative to sham treated animals is macrophage-dependent. Macrophage supernatants from burned mice released twice as much IL-6 as supernatants from sham animals (P<0.05), and when IL-6 was blocked in vivo, the amount of IFN-gamma production in burned mice decreased to sham levels (P<0.05). Thus, IL-6 mediates IFN-gamma production following burn.     

Prostaglandin E2 inhibits Paracoccidioides brasiliensis killing by human monocytes

Human monocytes lacked fungicidal activity against high virulence strain of Paracoccidioides brasiliensis, even after IFN-gamma activation. However, monocytes treated with indomethacin exhibited an effective killing against this fungus, suggesting a role of prostaglandin E2 (PGE2) in the inhibition process. Thus, the purpose of this work was to determine whether the effect of PGE2 in fungicidal activity was related with decrease on H(2)O(2) release, the metabolite involved in P. brasiliensis killing, and changes in the levels of TNF-alpha, IL-6 and IL-10. Human monocytes challenged with the fungus produced high PGE2 levels, which in turn inhibited the fungicidal activity of these cells by reducing H(2)O(2) and TNF-alpha production.     

Differential induction of TGF-beta regulates proinflammatory cytokine production and determines the outcome of lethal and nonlethal Plasmodium yoelii infections

Transforming growth factor-beta is an essential moderator of malaria-induced inflammation in mice. In this study, we show that the virulence of malaria infections is dependent upon the cellular source of TGF-beta and the timing of its production. C57BL/6 mice infected with a nonlethal (Py17X) strain of Plasmodium yoelii produce TGF-beta from 5 days postinfection; this correlates with resolution of parasitemia, down-regulation of TNF-alpha, and full recovery. In contrast, infection with the lethal strain Py17XL induces high levels of circulating TGF-beta within 24 h; this is associated with delayed and blunted IFN-gamma and TNF-alpha responses, failure to clear parasites, and 100% mortality. Neutralization of early TGF-beta in Py17XL infection leads to a compensatory increase in IL-10 production, while simultaneous neutralization of TGF-beta and IL-10R signaling leads to up-regulation of TNF-alpha and IFN-gamma, prolonged survival in all, and ultimate resolution of infection in 40% of Py17XL-infected animals. TGF-beta production can be induced in an Ag-specific manner from splenocytes of infected mice, and by cross-linking surface CTLA-4. CD25(+) and CD8(+) cells are the primary source of TGF-beta following Py17X stimulation of splenocytes, whereas Py17XL induces significant production of TGF-beta from adherent cells. In mice immunized against Py17XL, the early TGF-beta response is inhibited and is accompanied by significant up-regulation of IFN-gamma and TNF-alpha and rapid resolution of challenge infections.     

Tumor necrosis factor, interleukin-1 and interleukin-8 mediate the nociceptive activity of the supernatant of LPS-stimulated macrophages

It has been suggested that the supernatant of LPSstimulated macrophages (macrophage nociceptive factor, MNF) promotes nociception in mice. Intraperitoneal administration of MNF induced dose-related writhing, which reached a plateau between 18 and 26 min after injection and decreased within 60 min. The release of MNF was inhibited by the pretreatment of the macrophages with cycloheximide, a protein synthesis inhibitor, or with the glucocorticoid dexamethasone. Cyclooxygenase inhibitors, such as indomethacin or paracetamol, had no effect. The MNF-induced nociception was inhibited in a dose-related manner by pretreatment of the animals with indomethacin, paracetamol or dexamethasone. Pretreatment of the animals with the sympatholytics guanethidine and atenolol partially reduced the MNF nociception, which was abolished by the combination of guanethidine or atenolol with indomethacin. The preincubation of MNF with antisera against TNF-alpha, IL-1 or IL-8 partially inhibited its nociceptive effect. Intraperitoneal injection of a mixture of the recombinants cytokines TNF-alpha, IL-1 and IL-8 mimicked MNF nociception. The individual injection of these cytokines was unable to induce the nociceptive effect. In conclusion, our data suggest that the nociceptive activity of the supernatant of LPSstimulated macrophages is explained by the presence of TNF-alpha, IL-1 and IL-8, the nociceptive activity of which (in mice) seems to be due to the release of cyclooxygenase and sympathetic metabolites.     

Modulation of macrophage phenotype by soluble product(s) released from neutrophils

The regulation of macrophage phenotype by neutrophils was studied in the s.c. polyvinyl alcohol sponge wound model in mice made neutropenic by anti-Gr-1 Ab, as well as in cell culture. Wounds in neutropenic mice contained 100-fold fewer neutrophils than those in nonneutropenic controls 1 day after sponge implantation. Wound fluids from neutropenic mice contained 68% more TNF-alpha, 168% more IL-6, and 61% less TGF-beta1 than those from controls. Wound fluid IL-10 was not different between the two groups, and IL-4 was not detected. Intracellular TNF-alpha staining was greater in cells isolated from neutropenic wounds than in those from control wounds. The hypothesis that wound neutrophil products modulate macrophage phenotype was tested in Transwell cocultures of LPS-stimulated J774A.1 macrophages and day 1 wound cells (84% neutrophils/15% macrophages). Overnight cocultures accumulated 60% less TNF-alpha and IL-6 than cultures of J774A.1 alone. The suppression of cytokine release was mediated by a soluble factor(s), because culture supernatants from wound cells inhibited TNF-alpha and IL-6 release from LPS-stimulated J774A.1 cells. Culture supernatants from purified wound neutrophils equally suppressed TNF-alpha release from LPS-stimulated J774A.1 cells. Wound cell supernatants also suppressed TNF-alpha and superoxide release from murine peritoneal macrophages. The TNF-alpha inhibitory factor has a molecular mass <3000 Da and is neither PGE2 nor adenosine. The present findings confirm a role for neutrophils in the regulation of innate immune responses through modulation of macrophage phenotype.     

Carcinogen-induced inflammation and immunosuppression are enhanced in xeroderma pigmentosum group A model mice associated with hyperproduction of prostaglandin E2

Xeroderma pigmentosum group A (XPA) gene-deficient mice easily developed skin cancers by the application of topical chemical carcinogens as well as by UV irradiation. As certain chemical carcinogens have been shown to be immunosuppressive, we examined the inflammatory and immunosuppressive effects of dimethylbenz(a)anthracene (DMBA) on XPA mice. Compared with wild-type mice, XPA mice showed greater ear swelling and reduction of epidermal Langerhans cells after DMBA application. Topical application of DMBA impaired the induction of contact hypersensitivity, initiated either locally or at distant sites. These DMBA-induced local and systemic immunosuppressions were more greatly enhanced in XPA mice than in wild-type mice. DMBA application induced pronounced production of PGE(2), IL-10, and TNF-alpha in the skin of XPA mice. Treatment with indomethacin, a potent inhibitor of PG biosynthesis, inhibited DMBA-induced inflammation and local immunosuppression. In XPA mice, increased serum IL-10 was detected after DMBA treatment. Excess production of PGE(2), TNF-alpha, and IL-10 after DMBA application may be involved in the enhanced local and systemic immunosuppression in DMBA-treated XPA mice. Susceptibility to DMBA-induced skin tumors in XPA mice may be due to easy impairment of the immune system by DMBA in addition to a defect in the repair of DMBA-DNA adduct. Enhanced immunosuppression by chemical carcinogens as well as the mutagenicity of these mutagens might be associated with the high incidence of internal malignancies seen in XP patients. Moreover, these results supported the hypothesis that persistent DNA damage is a trigger for the production of immunoregulatory cytokines.     

Protective and memory immunity to Histoplasma capsulatum in the absence of IL-10

We determined whether the absence of IL-10 in mice influenced protective and memory immunity to Histoplasma capsulatum. IL-10(-/-) mice cleared primary and secondary infection more rapidly than wild-type controls. Administration of mAb to TNF-alpha or IFN-gamma, but not GM-CSF, abrogated protection in naive IL-10(-/-) mice; mAb to TNF-alpha, but not IFN-gamma or GM-CSF, subverted protective immunity in secondary histoplasmosis. The inflammatory cell composition in IL-10(-/-) mice was altered in those given mAb to IFN-gamma or TNF-alpha. More Gr-1(+) and Mac-3(+) cells were present in lungs of IL-10(-/-) mice given mAb to IFN-gamma, and treatment with mAb to TNF-alpha sharply reduced the number of CD8(+) cells in lungs of IL-10(-/-) mice. We ascertained whether the lack of IL-10 modulated memory T cell generation or the protective function of cells. The percentage of CD3(+), CD44(high), CD62(low), and IFN-gamma(+) cells in IL-10(-/-) mice was higher than that of wild-type at day 7 but not day 21 or 49 after immunization. Fewer splenocytes from immunized IL-10(-/-) mice were required to mediate protection upon adoptive transfer into infected TCR alphabeta(-/-) mice. Hence, deficiency of IL-10 confers a salutary effect on the course of histoplasmosis, and the beneficial effects of IL-10 deficiency require endogenous TNF-alpha and/or IFN-gamma. Memory cell generation was transiently increased in IL-10(-/-) mice, but the protective function conferred by cells from these mice following immunization is strikingly more vigorous than that of wild-type.     

Prostaglandin E2-mediated suppression of murine lymphokine-activated killer cell activity generated from tumor-bearing hosts by interferon-gamma

The effect of mouse recombinant interferon-gamma (IFN-gamma) on murine lymphokine-activated killer (LAK) cell activity was investigated using a natural killer-resistant, LAK-sensitive, spontaneously developed, weakly immunogenic, syngeneic murine mammary adenocarcinoma, a tumor model mimicking that of human disease. When all of the splenocytes prepared from tumor-bearing mice were cultured with recombinant interleukin-2 (IL-2) and IFN-gamma, LAK cell activity was suppressed in an IFN-gamma dose-dependent manner. An increase in the prostaglandin E2 (PGE2) content in the corresponding culture media was detected, as was IFN-gamma dose dependent. The suppression of generation of LAK cell activity by IFN-gamma was abrogated, accompanied by the elimination of the increase in PGE2 content, when plastic dish and nylon wool-treated nonadherent macrophage-depleted splenocytes were used. These results indicated that IL-2-induced LAK cell activity generated from the splenocytes of tumor-bearing mice was suppressed by IFN-gamma, and that PGE2 secreted from the macrophages of the splenocyte cultures served as the mediator in this IFN-gamma dose-dependent suppression of IL-2-induced LAK cell activity.     

Mechanisms of strain-dependent development of mast cells from mouse splenocytes

Mast cell development from spleen cells was not triggered by prostaglandin E1 (PGE1) or dibutyryl cAMP (db-cAMP) during a 12 day culture when the spleen cells were obtained from C57BL/6N and DBA/1 mice, but mast cells did develop when the spleen cells were obtained from C3H/HeN, BALB/c and ICR mice. A lack of endogenous IFN-gamma in the initial 2 days of the culture period was responsible for the failure. This was confirmed by adding neutralizing anti-IFN-gamma antibody and rIFN-gamma to the cultures and by determining IFN-gamma levels in the spleen cell cultures. Th1 cells in the spleens of C57Bl and DBA/1 mice were much more sensitive to PGE1 and db-cAMP than Th1 cells from other inbred mice strains, and consequently, IFN-gamma production was inhibited in spleen cell cultures of C57BL and DBA/1 mice on addition of PGE1 or db-cAMP. Furthermore, the different sensitivities of Th1 cells to PGE and db-cAMP were dependent on the different levels of IL-12 p40 monomers or homodimers in the spleen cell cultures. As the endogenous specific inhibitors of IL-12 p70 (heterodimers of p40 and p35), large amounts of IL-12 p40 monomers or homodimers in the spleen cell cultures of C57BL and DBA/1 mice enhanced the ability of PGE1 and db-cAMP to inhibit IFN-gamma production by antagonizing the activity of IL-12 heterodimers. These results indicate that the strain-dependent development of mast cells from mouse splenocytes is related to endogenous IFN-gamma levels, which are regulated by PGE, db-cAMP, IL-12 p70 and IL-12 p40.     

Mu-opioid receptor mediates chronic restraint stress-induced lymphocyte apoptosis

Psychological stress is associated with immunosuppression in both humans and animals. Although it was well established that psychological stressors stimulate the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system, resulting in the release of various hormones and neurotransmitters, the mechanisms underlying these phenomena are poorly understood. In this study, mu-opioid receptor knockout (MORKO) mice were used to investigate whether the mu-opioid receptor mediates the immunosuppression induced by restraint stress. Our results showed that wild-type (WT) mice subjected to chronic 12-h daily restraint stress for 2 days exhibited a significant decrease in splenocyte number with a substantial increase in apoptosis and CD95 (Fas/APO-1) expression of splenocytes. The effects are essentially abolished in MORKO mice. Furthermore, inhibition of splenic lymphocyte proliferation, IL-2, and IFN-gamma production induced by restraint stress in WT mice was also significantly abolished in MORKO mice. Interestingly, both stressed WT and MORKO mice showed a significant elevation in plasma corticosterone and pituitary proopiomelanocortin mRNA expression, although the increase was significantly lower in MORKO mice. Adrenalectomy did not reverse restraint stress-induced immunosuppression in WT mice. These data clearly established that the mu-opioid receptor is involved in restraint stress-induced immune alterations via a mechanism of apoptotic cell death, and that the effect is not mediated exclusively through the glucocorticoid pathway.     

Regulation of synovial cell proliferation and prostaglandin E2 production by combined action of cytokines

To study the causes of synovitis in rheumatoid arthritis (RA), we have analyzed the effect of several cytokines known to be secreted in RA joints, on synovial cell proliferation and prostaglandin E2 (PGE2) production. Recombinant interleukin-1-beta (IL-1-beta) and tumor necrosis factor-alpha (TNF-alpha) stimulated moderately the DNA synthesis and markedly the production of PGE2. Interferon-gamma (IFN-gamma) was often mitogenic but never induced PGE2 secretion. The association of IL-1-beta and TNF-alpha showed an additive effect on both parameters, whereas addition of IFN-gamma to either monokine reduced the proliferation and increased PGE2 release. Incubation with a crude T cell supernatant or a mixture of cytokines including IL-1-beta, TNF-alpha and IFN-gamma enhanced synovial cell growth and PGE2 production as compared to the effect elicited by each single cytokine. In contrast, interleukin-2 (IL-2) down regulated the synovial cell activation induced by the combined action of the three other cytokines. Taken together, our findings indicate that synovial cell proliferation is weakly stimulated, reaching a two-fold increase over background levels, whatever cytokines are used. Furthermore, proliferation can vary independently of PGE2 production. Nevertheless, the monokines IL-1-beta and TNF-alpha both exert agonistic effects on synovial cell activation, thus contributing to cartilage damage in RA, whereas IFN-gamma, IL-6 or IL-2 may rather play a regulatory role.     

Leukotrienes play a role in the control of parasite burden in murine strongyloidiasis

It is clear that leukotrienes mediate inflammatory response; new aspects of leukotriene function have recently been described. In this study, we demonstrate that leukotrienes are key chemical mediators in the control of parasite burdens in mice infected with Strongyloides venezuelensis. High leukotriene levels were detected in the lungs and small intestines of Swiss mice. In infected Swiss mice treated with MK886, a leukotriene synthesis inhibitor, numbers of adult worms, and eggs/g/feces were greater than in infected-only animals. The MK886 treatment inhibited leukotriene B(4) production in the lungs and small intestines, albeit on different postinfection days. Similarly, parasite burdens and eggs/g/feces were greater in 5-lipoxygenase(-/-) mice than in wild-type animals. These observation were confirmed by histopathological study of the duodena. We subsequently observed significant lower numbers of eosinophils and mononuclear cells in the blood, peritoneal cavity fluid, and bronchoalveolar lavage fluid of Swiss mice treated with MK886. In the lung parenchyma of infected animals, MK886 significantly inhibited synthesis of IL-5 at the beginning of infection, whereas levels of IL-12 increased progressively throughout the postinfection period. However, levels of leukotriene C(4), PGE(2), TNF-alpha, IL-3, IL-4, IFN-gamma, and IL-10 were comparable between the treated and untreated groups. Nevertheless, IgE and IgG1 (but not IgG2a) synthesis was also significantly inhibited by MK886 administration. Therefore, in S. venezuelensis-infected mice, adult worm and egg burdens are leukotriene dependent. These findings indicate potential immunostimulatory strategies involving leukotriene administration, and may serve as an alert to physicians treating Strongyloides stercoralis-infected patients presenting asthma-like symptoms because use of 5-lipoxygenase inhibitors may worsen the infection.     

Inflammatory cytokine production in interferon-gamma-primed mice, challenged with lipopolysaccharide. Inhibition by SK&F 86002 and interleukin-1 beta-converting enzyme inhibitor

Mice challenged with lipopolysaccharide (LPS) produce variable serum levels of pro-inflammatory cytokines, and particularly low levels of interleukin-1 beta (IL-1 beta). Interferon-gamma (IFN-gamma) has been shown to be an important mediator of bacteria-induced hypersensitivity to LPS in mice. In the present study, we show that mice pretreated with IFN-gamma exhibit an enhanced capacity to produce serum IL-1 beta, IL-1 alpha, tumour necrosis factor (TNF-alpha) as well as IL-6 in response to LPS. Priming with intraperitoneal (i.p.) injection of 15 mg rat recombinant IFN-gamma, 18 hours prior to the i.p. LPS (300 mg) challenge resulted in a 4-fold increase in the LPS-stimulated release of IL-1 beta and a 2- to 7-fold increase in the release of IL-1 alpha, TNF-alpha, as well as IL-6 into the serum. LPS induced a concentration-dependent increase in the release of IL-1 beta in isolated peritoneal macrophages from IFN-gamma-primed mice whereas macrophages from unprimed mice released minute amounts of IL-1 beta. In addition, nigericin markedly enhanced the release of IL-1 beta in unprimed mice but not in macrophages from IFN-gamma primed mice. The cytokine synthesis inhibitor SK&F 86002, administered per os (100 mg/kg), 1 hour prior to LPS challenge, strongly inhibited the rise in serum levels of the four cytokines. Furthermore, treatment with the IL-1 beta converting enzyme (ICE) specific reversible inhibitor YVAD-CHO resulted in a sharp dose- and time-dependent inhibition of IL-1 beta secretion in the serum, whereas the other cytokines were not affected. In conclusion, IFN-gamma priming strongly potentiates the release of proinflammatory cytokines in the serum of mice as compared to LPS stimulation alone, and provides therefore a useful way to test the in vivo potency and selectivity of cytokine synthesis inhibitors.     

The cytokine balance in the maintenance of a persistent infection with Salmonella enterica serovar Typhimurium in mice

ClpXP, serine protease-disrupted mutant of Salmonella enterica serovar Typhimurium chi3306 exhibits attenuated but persistent infection in mice. During infection with S. enterica serovar Typhimurium ClpXP-disrupted mutant, gamma interferon (IFN-gamma) produced by CD4+ cells was up-regulated on day 10 and tumor necrosis factor-alpha (TNF-alpha) produced by CD8+ cells was up-regulated on day 30 after infection. Treatment of monoclonal antibodies against cytokines showed that IFN-gamma and interleukin 10 (IL-10) were involved in maintenance of growth of S. Typhimurium mutant on day 10 after infection, and IFN-gamma, TNF-alpha and transforming growth factor-beta (TGF-beta) were involved in maintenance of growth of this bacterium on day 30 after infection. During persistent infection of S. Typhimurium mutant, IFN-gamma, TNF-alpha, IL-10 and TGF-beta may play different roles to maintain the persistent infection. The cytokine balance might be important in persistent infection with ClpXP-disrupted S. enterica serovar Typhimurium.     

Cytokine-induced neutrophil chemoattractant 1 (CINC-1) mediates the sympathetic component of inflammatory mechanical hypersensitivitiy in rats

The hyperalgesic effect of cytokine-induced neutrophil chemoattractant 1 (CINC-1/CXCL1) was measured in a model of mechanical hyperalgesia in rats. CINC-1 evoked a dose-dependent mechanical hypersensitivity, which was already significant 2 h after the cytokine injection, peaked 4 h after and decreased thereafter. The local pre-treatment of the rats with the beta-adrenoceptor antagonist, atenolol (25 microg paw-1), but not with the cyclooxygenase inhibitor indomethacin (100 microg paw-1), inhibited (86%) the CINC-1-induced hypersensitivity. Conversely, IL-1beta-evoked hypersensitivity was inhibited (76%) by local pre-treatment of the animals with indomethacin, but not by atenolol. Carrageenin- and TNF-alpha-evoked hypersensitivity were attenuated to about the same extent (50%) by antisera neutralising CINC-1 or IL-1beta. The association of both antisera abolished the hypersensitivity effect of carrageenin and TNF-alpha. In addition, carrageenin, LPS and TNF-alpha were shown to stimulate the production of immunoreactive CINC-1 in the skin of injected paws. These data suggest that CINC-1, released at sites of inflammation, mediates inflammatory hyperalgesia in rats via release of sympathomimetic amines.     

Production of cytokines by peritoneal macrophages and splenocytes after exposures of mice to low doses of X-rays

We have shown previously that irradiations of mice with 0.1 or 0.2 Gy of X-rays stimulate anti-tumour cytotoxic activities of peritoneal macrophages and splenocytes enriched for NK lymphocytes and suppress the development of pulmonary tumour colonies. The up-regulated cytotoxicities were related to the production of nitric oxide by macrophages, and perforin and Fas ligand by the splenocytes, but specific blockade of these pathways did not totally suppress the effector cell-mediated cytolysis of the tumour target. Hence, other factors such as cytotoxic/cytostatic cytokines might have been produced by the effector cells. To test this possibility peritoneal macrophages and splenocytes were isolated from BALB/c mice which had been either once or tentimes whole body-irradiated with the total doses of 0.1 and 0.2 Gy of X-rays and assayed for the levels of IL-1beta, IL-2, IL-12, IFN-gamma and TNF-alpha in the incubation medium using the respective ELISA kits. The results demonstrate that both single and multiple exposures to the two low doses of X-rays significantly stimulate secretion of IL-1beta, TNF-alpha and IL-12 by macrophages and IL-2 and IFN-gamma by splenocytes, but the kinetics and magnitude of the induced changes in the production of these cytokines differ between the two irradiation protocols.     

Helicobacter pylori-secreted factors inhibit dendritic cell IL-12 secretion: a mechanism of ineffective host defense

Helicobacter pylori evades host immune defenses and causes chronic gastritis. Immunity against intestinal pathogens is largely mediated by dendritic cells, yet the role of dendritic cells in acute H. pylori infection is largely unknown. We observed the recruitment of dendritic cells to the gastric mucosa of H. pylori-infected mice. Bone marrow-derived dendritic cells from mice responded to live H. pylori by upregulating the expression of proinflammatory cytokine mRNA (i.e., IL-1alpha, IL-1beta, and IL-6). The supernatant from dendritic cells stimulated with H. pylori for 18 h contained twofold higher levels of IL-12p70 than IL-10 and induced the proliferation of syngeneic splenocytes and type 1 T helper cell cytokine release (IFN-gamma and TNF-alpha). These responses were significantly lower compared with those induced by Acinetobacter lwoffi, another gastritis-causing pathogen more susceptible to host defenses. Analysis of whole H. pylori sonicate revealed the presence of a heat-stable factor secreted from H. pylori that specifically inhibited IL-12 but not IL-10 release from dendritic cells activated by A. lwoffi. Our findings suggest that dendritic cells participate in the host immune response against H. pylori and that their suppression by H. pylori may explain why infected hosts fail to prevent bacterial colonization.