Plaque-forming Cell Response Research Articles

Halogenated aromatic hydrocarbon-induced suppression of the plaque-forming cell response in B6C3F1 splenocytes cultured with allogenic mouse serum: Ah receptor structure activity relationships

The immunsuppressive effects of halogenated aromatic hydrocarbons (HAHs) were investigated in B6C3F1 female mice and in mouse splenocytes cultured with allogenic mouse serum using the Mishell-Dutton model for in vitro immunization to trinitrophenyl-lipopolysaccharide (TNP-LPS). Exposure to 2,3,7,8-tetrachlorodibenzo- P-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), 1,2,3,7,8-PeCDF, 1,3,6,8-tetrachlorodibenzofuran (TCDF), 3,3′,4,4′,5-pentachlorobiphenyl (pentaCB), or 3,3′,4,4′,5,5′-hexaCB resulted in a dose-dependent suppression of the splenic plaque-forming cell (PFC) response both in vivo and in vitro. The effective dose required to decrease 50% (ED 50) of the response to 2,3,7,8-TCDD, 2,3,4,7,8-PeCDF, 1,2,3,7,8-PeCDF, 1,3,6,8-TCDF, 3,3′,4,4′,5-pentaCB, or 3,3′,4,4′,5,5′-hexaCB in vivo was 14.1, 5.5, 1695, 34800, 21, and 19 nmol/kg, respectively, and in vitro was 7.0, 10.6, 149, 2325, 9.1 and 9.1 nM, respectively. There was an excellent rank order and linear correlation between the in vivo versus in vitro activities for these HAHs ( r < 0.99) and the relative immunosuppressive potencies of these compounds paralleled their binding affinities for the aryl hydrocarbon (Ah) receptor. These results show that splenocytes cultured with allogenic mouse serum is an Ah-responsive in vitro assay which can be used for quantitating the immunosup-pressive effects of HAHS.

Immunological effects of 2-methoxyethanol administered dermally or orally to Fischer 344 rats

Exposure of rats to 2-methoxyethanol (ME) by gavage for 10 consecutive days results in immunotoxicity. To determine whether dermal exposure to ME also induces immunotoxicity, undiluted ME was applied to Fisher 344 male rats at dose levels of 150, 300, 600, 900 or 1200 mg/kg/day on shaved occluded test sites for 4 consecutive days. Decreased thymus weights were produced by all doses of ME, while reductions in spleen weight were observed at doses of 900 mg/kg/day ME or greater. The alterations in these lymphoid organ weights were produced in the absence of loss in body weight. The lymphoproliferative (LP) responses to phytohemagglutinin (PHA) and pokeweed mitogen (PWM) were enhanced at 1200 mg/kg/day ME compared with water controls. Separate groups of rats, employed for the antibody plaque-forming cell (PFC) response to either trinitrophenyl-lipopolysaccharide (TNP-LPS) or sheep red blood cells (SRBC), were exposed dermally to 150, 300 or 600 mg/kg/day ME for 4 consecutive days. A reduction in the PFC response to TNP was observed at 600 mg/kg/day ME, whereas decreases in the PFC response to SRBC were observed at dosages of 300 and 600 mg/kg/day ME. To compare the immunotoxic effects of dermally applied ME to those effects caused by ME administered orally, rats were dosed by gavage with 25, 50, 100 or 200 mg/kg/day ME in distilled water for 4 consecutive days. Reductions in thymus weights were observed at oral dosages ranging from 50–200 mg/kg/day, while spleen weights were reduced in rats dosed at 200 mg/kg/day ME. LP responses to PHA, PWM and Salmonella typhimurium were increased at the 200 mg/kg/day ME dose level. PFC responses to TNP-LPS and SRBC were suppressed at the 50, 100 and 200 mg/kg/day ME dosages. These results indicate that, like oral exposure, dermal exposure to ME compromises the ability of the immune system to mount an effective humoral immune response.

Opioid receptor-mediated suppression of humoral immune response in vivo and in vitro: involvement of κ opioid receptors

The selective κ opioid receptor agonist MR 2034 exerted pronounced suppression of plaque-forming cell (PFC) response following intraperitoneal (i.p.) administration in the rat. Pretreatment with preferential κ and μ opioid receptor antagonists MR 2266 and naloxone, respectively, revealed that this effect was mediated mainly by κ, and to a low extent by μ opioid receptors. Intracerebroventricular (i.c.v.) administration of quaternary naltrexone (QNtx) moderately attenuated, whereas i.p. given QNtx completely prevented the suppressive effect of MR 2034, suggesting a peripheral mechanism of action, and only minor involvement of brain opioid receptors. MR 2034 markedly decreased the PFC response of spleen cells obtained from in vivo immunized rats, treated in vitro with the opiate. The immunosuppressive action of MR 2034 in vitro was completely and partially blocked by equimolar concentrations of MR 2266 and naloxone, respectively. Antagonists alone produced stimulation of PFC following i.p. administration in the rat, but did not affect PFC response upon in vitro treatment. These results suggest that peripheral k opioid receptors down-regulate primary humoral immune response in the rat, and that this effect may be produced by direct interference with plasma cell activity.

Modulation of primary antibody response by protein A in tumor bearing mice.

Protein A (PA) is a cell wall glycoprotein of Staphylococcus aureus Cowan I, which possess a number of immunomodulatory and antitumor properties. We have previously shown that PA suppresses the anti-sheep erythrocyte primary antibody response in normal mice. The present investigation evaluates the effect of protein A on the anti-sheep erythrocyte primary antibody response in tumor-bearing mice. The primary antibody response in tumor-bearing mice immunized with sheep red blood cells (SRBC) was suppressed by the intraperitoneal administration of PA in a dose-dependent fashion. The plaque forming cell (PFC) assay was used to assess this response. Maximum suppression of the PFC response was observed at 12 micrograms PA/animal (p < 0.001) and could be observed at doses as low as 1 microgram PA/animal (p < 0.01). The amount of suppression was proportional to the number of PA doses administered. In addition this effect was critically dependent on the timing of PA administration. PA showed no significant effect on PFC when injected after immunization, but it produced pronounced suppression when injected prior to the immunization with SRBC. Maximum suppression of the PFC response was observed when PA was administered one day before the antigen challenge. PA also reduced splenic localization of 51Cr labeled SRBC to 42% (p < 0.01). The altered localization of antigen in spleen may be responsible for reduced PFC response in tumor-bearing mice. Depletion of B-lymphocyte is reported to exhibit tumor inhibition. Therefore, we propose that the suppression of the primary antibody response by PA helps in tumor regression by reducing the soluble immunosuppressive immune complexes.

Rapid communication: effect of irradiation on lymphocyte proliferation and differentiation: potential of IL-6 in augmenting antibody responses in cultures of murine spleen cells.

Ionizing radiation induces both quantitative and qualitative changes in the lymphoid cells of both man and experimental animals, including inhibition of antibody responses. However, the cellular basis of this immunological lesion is not clear. In the present study, groups of mice were exposed to 2.0 Gy gamma-rays or sham irradiated, and 2 days later animals were killed and spleen cells were cultured with TNP-Ficoll and assayed for antibody responses. Results indicated a significant decrease in the number of anti-TNP, plaque-forming cells in cultures from the irradiated mice compared with cultures from the control. When lymphocytes were stimulated in vitro with anti-IgM or anti-CD3, there was a decreased proliferation in spleen cell cultures derived from the irradiated mice compared with those from the control. Since radiation treatment was found to deplete both T and B cells in equal proportions in spleen and an equal number of both control or treated cells were used in culture, the immunological abnormalities may have been due to intrinsic defects in irradiated cells. Addition of IL-6 to irradiated spleen cell cultures was able to augment anti-TNP, plaque-forming cell responses indicating the possibility that in the future this cytokine can be used in vivo to induce protection from infectious diseases in irradiated individuals.

Influence on HMG-COA reductase inhibitors on plaque-forming cell (PFC) response in mice.

Effects of pravastatin and simvastatin on the humoral immune response were studied using Cunningham's method of the IgM plaque-forming cell (PFC) assay system in mice. The vehicle (0.5% CMC), pravastatin (1 mg/body : about 50 mg/kg) or simvastatin (0.5 mg/body : about 25 mg/kg) were given orally for 14 days in experiment Exp-I and Exp-II. The vehicle, pravastatin (0.5 mg/body : about 25 mg/kg) or simvastatin (0.25 mg/body : about 12.5 mg/kg) were given orally 29 times for 32 days in Exp-III. There were no significant differences in the mean numbers of PFCs per 10(6) splenocytes between the pravastatin groups and the vehicle groups. In the simvastatin groups, however, there were significant reductions of the numbers of PFCs in Exp-I, Exp-II and Exp-III, as compared with the vehicle group. Based on these results, it was considered that suppressive effect on IgM antibody production was induced by simvastatin, whereas such a suppression was not observed with pravastatin.

Immunosuppressive Activity of Polychiorinated Biphenyl Mixtures and Congeners: Nonadditive (Antagonistic) Interactions

The dose-response inhibition of the splenic plaque-forming cell (PFC) response and serum IgM units to the antigen, trinitrophenyl-lipopolysaccharide, was determined for several polychiorinated biphenyl (PCB) mixtures and congeners in female B3C3F1 mice. The ED50 values for Aroclor 1260-, 1254-, 1248-, and 1242-induced immunotoxicity varied by less than twofold from 355 to 699 mg/kg. The range of ED50 values for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3′ ,4,4′-tetrachlorobiphenyl, 3,3′ ,4,4′,5-pentaCB, 3,3′,4,4′,5,5′-hexaCB, 2,3,3′,4,4′-pentaCB, 2,3′,4,4′,5-pentaCB, 2,3,3′,4,4′,5-hexaCB, 2,3,3′,4,4′,5,5′-heptaCB, 2,2′,3,3′,4,4′,5-heptaCB, and 2,2′,3,4,4′,5,5′-heptaCB were 4.6 to 4.9, 134 to 245, 4.7 to 7.0, 6.9 to 11.1, 88,000 to 121,000, 122,000 to 132,000, 99,000 to 157,000, 89,000 to 129,000, 117,000 to 240,000, and 132,000 to 238,000 μg/kg, respectively. The immunotoxicity-derived toxic equivalency factors (TEFs) for these congeners could be calculated from the ED50 (TCDD)/ED50 (congener) ratios and the TEF values were within the range of those previously determined for other aryl hydrocarbon receptor-mediated responses. Based on the known concentrations of these congeners in the PCB mixtures, TCDD or toxic equivalents (TEQs) in the mixture were calculated [i.e., TEQ = Σ(PCBcongener × TEF)] using the immunotoxicity-derived TEFs (plaque-forming cells/106 viable cells). TEQ values for Aroclors 1260, 1254, 1248, and 1242 were 16.0, 54.4, 260.4, and 197 ppm, respectively. Based on the ED50 value for the immunosuppressive activity of TCDD (4.8 μg/kg), the calculated ED50 values for immune suppression by Arodors 1260, 1254, 1248, and 1242 were 300, 88, 18, and 24 mg/kg, respectively. The ED50 (observed)/ED50 (calculated) ratios were 1.2, 5.9, 21, and 22.0 for Aroclors 1260, 1254, 1248 and 1242, respectively. Thus, for Aroclors 1254, 1248, and 1242, the high ED50 (observed)/ED50 (calculated) ratios (i.e., 5.9 to 22.0) indicate that the TEF approach overestimates the toxicity of these mixtures due to non-additive (antagonistic) interactions of the PCBs. In contrast, the TEF approach was useful in determining the immunotoxicity of the Aroclor 1260 mixture.

Pretent status and problems with the methods for testing immunotoxicity.

Immunotoxicology has become a very important field because of the immunological adverse effects of various cytokines (IL-2 and IFNα, etc.) and biological response modifiers in addition to the immunosuppression caused by steroid hormones and anticancer agents and drug (antibiotic)-induced allergies. The adverse effects include the development of infectious diseases or various cancers due to immunosuppression and the occurrence of allergies or autoimmunity due to immunopotentiation. Studies to establish testing guidelines were done worldwide using immunosuppressants (azathioprine and cyclosporin A), and the most suitable marker or test system to detect immunotoxicity of xenobiotics was explored. Moreover, the necessity of immunotoxicity studies is stressed in “Redbood II” (FDA, draft; 1993). In experiments on thymus toxicity in the rat, the following data were obtained. The weight of the thymus increased from birth until 8 weeks of age and then decreased gradually. The weight was also decreased by stress induced by factors such as fasting, the attachment of an Elizabeth collar, etc. and the administration of cyclophosphamide (immunosuppressant). This drug caused degenerative changes in the thymus, spleen, and bone marrow and inhibited the plaque forming cell response to sheep red blood cells in rats. TGP-3 (human recombinant interleukin 2) caused fever via the production of interleukin 1β and increased the number of eosinophils. When the immune system was suppressed by exposure to 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) or chronic administration of an immunosuppressant (cyclophosphamide), the susceptibility to infectious diseases and tumor formation was increased. On the other hand, when the action of the immune system was potentiated by the repeated administration of an immunomodulator (antirheumatic agent), autoimmune diseases rarely occurred. The importance of immunotoxicology and future directions for immunotoxicity testing are discussed in this paper.

Alterations in central catecholamines associated with immune responding in adult and aged mice

Central catecholamine alterations associated with immune activity are similar to those seen following stressor exposure. Inasmuch as aged animals exhibit more pronounced stressor-provoked alterations of central amines relative to younger animals, it was of interest to determine whether immune challenge would similarly induce more pronounced central amine variations in older animals. Fifteen-month old CD-1 mice challenged with 10 7 sheep red blood cells (SRBC) revealed an equivalent peak splenic plaque-forming cell response (4 days after antigen challenge) to that of 3-month-old mice challenged with 10 6 cells. Neither plasma adrenocorticotropic hormone (ACTH) nor corticosterone levels varied over days following immunization, although ACTH levels were generally higher in the older mice. In both age groups reductions of hypothalamic and locus coeruleus norepinephrine (NE) and increased accumulation of the metabolite MHPG coincided with (or preceded by 24 h) the peak immune response. However, increased accumulation of MHPG in the hypothalamus was greater and occurred earlier in the locus coeruleus of the aged mice. Likewise, at or about the time of peak immune responses nucleus accumbens dopamine (DA) levels were reduced and metabolites elevated in both age groups, while in the prefrontal cortex only DA metabolite levels were elevated. These data are commensurate with previous findings showing that SRBC inoculation may influence central neurotransmitters and that such effects correspond with the time of the peak immune responses. Moreover, in so far as hypothalamic NE utilization is concerned, it seems that the effects of SRBC inoculation are more pronounced in aged animals.

Relative Sensitivities of 2,3,7,8-Tetrachlorodibenzo- p-dioxin-Induced Cyp1a-1 and Cyp1a-2 Gene Expression and Immunotoxicity in Female B6C3F1 Mice

Relative Sensitivities of 2,3,7,8 Tetracholorodibenzo- p-dioxin-Induced Cypla-1 and Cypla-2 Gene Expression and Immunotoxicity in Female B6C3F1 Mice. Narasimhan, T. R., Craig, A., Arellano, L., Harper, N., Howie, L., Menache, M., Birnbaum, L., and Safe, S. (1994). Fundam. Appl. Toxicol. 23, 598-607. Improvements in risk assessment require better linkage of exposure to response by the determination or target tissue dose. The relative sensitivity of several responses in female B6C3F1 mice was compared on the basis of administered and target tissue dose spanning 3 orders of magnitude. Twenty-four hours after administration, [ 3H]TCDD was detected in the heart, spleen, kidney, uterus, thymus, lung, and liver and the highest concentrations were noted in the liver, uterus, and lung. At doses from 5 to 25 ng/kg, hepatic [ 3H]TCDD levels associated with the cytosolic and nuclear subcellular fractions increased from 12 to 62% of the total liver levels and then decreased at higher doses. At the two lowest doses used in the enzyme induction study, 5 and 10 ng/kg, the levels of specifically bound nuclear Ah receptor complex liganded with [ 3H]TCDD were 2.3 and 2.5 fmol/mg protein. Slightly higher levels of nuclear Ah receptor complex were observed at doses between 25 and 100 ng/kg (i.e., 3.6 to 4.2 fmol/mg protein) and a steep dose-dependent increase in nuclear Ah receptor levels was noted at doses of 500, 1000, and 5000 ng/kg (8.0, 39.3, and 92.8 fmol/mg protein, respectively). The dose-dependent effects of [ 3H]TCDD on hepatic Cyp1a-1 and Cyp1a-2 mRNA levels, ethoxyresorufin O-deethylase (EROD) activity, and the splenic antibody plaque-forming cell (PFC) response to sheep red blood cells were also determined; the latter response was determined 9 days after administrations of TCDD. Statistically significant induction of hepatic Cyp1a-1 was observed at lower doses (25 ng/kg) than any other marker, followed by induction of EROD and PFCs expressed per spleen or per 10 6 cells which was observed at 100 ng TCDD/kg and at higher doses. Cyp1a-2 was elevated significantly relative to control at doses ⩾ 1000 ng/kg. The ED50 value for PFCs/106; cells was the lowest of the variables analyzed and was not statistically significantly different from control (91 ± 92 ng/kg). A 500% increase in Cyp1a-2 and Cyp1a-1 mRNA levels was observed at doses of 736 ± 132 and 1630 ± 431 ng/kg, respectively. Due to variability in response in PFCs/spleen and the submaximal induction of EROD activity, ED50 values could not be calculated for these responses. The analyses indicate that the immunosuppressive response (when normalized for the number of spleen cells) may be depressed by administered doses as low as 90 ng TCDD/kg body weight. A 50% in crease in Cyp1a-1 or Cyp1a-2 was observed at higher administered doses (1630 or 736 ng/kg, respectively). This suggests that the immunosuppressive response is depressed at lower doses of TCDD than the other variables studied.

Modulation of exercise‐induced immunosuppression by dietary polyunsaturated fatty acids in mice

The possible interaction between intense exercise, known to suppress the immune response, and nutritive factors, such as polyunsaturated fatty acids (PUFA), was examined in inbred female C57Bl/6 mice. The animals received for 8 wk either a natural ingredient diet or a diet supplemented with 10 g/100 g linseed oil containing over 50% of 18:3 (n-3) alpha-linoleic acid. Other groups received PUFA containing only traces of 18:3 (n-3) fatty acid; beef tallow, containing mostly 18:1 (n-9) saturated fat, safflower oil, an 18:2 (n-6) PUFA, and fish oil, containing longer chain (n-3) PUFA. Each dietary group was divided into two subgroups: sedentary diet controls and exercised animals. Exercise consisted of continuous swimming at high intensity until exhaustion. It was shown in three separate experiments that (1) the primary humoral response to sheep red blood cells, determined by the plaque-forming cell (PFC) assay, was affected by PUFA diet in sedentary animals in the order beef tallow > control diet > safflower oil > fish oil > linseed oil, and (2) the PFC response was suppressed by the exhaustive exercise, as compared to sedentary controls, except for animals fed 18:3 (n-3) linseed oil, where the normal response was noted. Phagocytosis of fluorescent microspheres by peritoneal macrophages, determined by flow cytometry, was significantly lower in exercised animals receiving the linseed oil diet, whereas other diets either increased or did not significantly change the macrophage phagocytic activity, compared to the sedentary diet controls. Spleen lymphocyte subsets were unchanged in exercised animals except for a marked shift from the lymphoid peak toward the erythroid peak. Generally, our data showed a marked immunomodulatory effect of 18-3 (n-3) alpha-linoleic acid on the exhaustive exercise-related immunosuppression, as compared to the effects of other selected PUFA.

Opposing activities of brain opioid receptors in the regulation of humoral and cell-mediated immune responses in the rat

The role of brain delta- and kappa-opioid receptors in the regulation of PFC response, Arthus hypersensitivity reactions and delayed hypersensitivity reactions was studied following intracerebroventricular (i.c.v.) administration of opioid receptor agonists and antagonists. Eight-week-old male Wistar rats, with polyethylene cannulae inserted into the lateral brain ventricles, were i.c.v. treated with different doses of delta-opioid receptor agonist methionine-enkephalin (Met-Enk), delta-opioid receptor antagonist ICI 174864, kappa-opioid receptor agonist MR 2034, and kappa-opioid receptor antagonist MR 2266. In rats sensitized for plaque-forming cell (PFC) assay, the first drug injection was given 1 h prior to immunization, and then every 24 h until day 4. One h after the last treatment, rats were sacrificed and (PFC) assay performed. In rats immunized for hypersensitivity skin reactions, the first drug injection was given 1 h before immunization, and then every 48 h until day 14. Skin reactions were elicited one h after the last drug administration. Opioid receptor agonists Met-Enk and MR 2034 stimulated and suppressed PFC response, Arthus and delayed skin reactions respectively. ICI 174864 decreased the number of PFC and intensity of hypersensitivity skin reactions whereas MR 2266 increased the number of PFC, but did not affect to a greater extent hypersensitivity reactions. Stimulation of PFC produced by 1 μg/kg of Met-Enk was completely blocked with 10 and 50 μg/kg of ICI 174864. MR 2034-induced suppression was partially and completely antagonized with 10 and 50 μg/kg of MR 2266 respectively. The present results suggest that brain opioid receptors differentially affect humoral and cell-mediated immune responses.

Quaternary naltrexone: its immunomodulatory activity and interaction with brain delta and kappa opioid receptors

To investigate the role of brain opioid receptors in immune reactions, quaternary naltrexone (QNtx), a nonselective opioid antagonist which does not cross the brain-blood barrier, was tested for its immunomodulatory activity and ability to antagonize immunological changes produced by centrally applied delta-receptor agonist methionine-enkephalin (Met-Enk) and kappa-opioid receptor agonist MR 2034. Plaque-forming cell (PFC) response served as an immunological model. For this purpose, different groups of Wistar rats were centrally (intracerebroventricularly, i.c.v.) and peripherally (intraperitoneally, i.p., or subcutaneously, s.c.) treated with different doses of Met-Enk, MR 2034 and QNtx. Centrally injected Met-Enk and MR 2034 induced a dose-dependent potentiation and suppression of PFC response, respectively. Small amounts of i.c.v. given QNtx produced a dose-dependent increase in the number of PFC, whereas peripherally administered antagonist potentiated immune response in a dose-independent manner. A dose of 10 μg/kg of QNtx given i.c.v. completely abolished the immunopotentiation by Met-Enk. However, a large dose of 5 mg/kg of QNtx given s.c., did not affect the Met-Enk-induced immunoenhancement. Immunosuppression produced by i.c.v. injected MR 2034 was totally abrogated by prior i.c.v. application of QNtx, but partially blocked by s.c. administration of the antagonist. These results suggest that: (a) QNtx itself potentiates the humoral immune response when applied centrally in small doses (1 to 10 μg/kg) or peripherally in relativelly large doses (0.2 to 5 mg/kg), (b) immunopotentiation and immunosuppression induced by i.c.v. given Met-Enk and MR 2034, respectively, appears to be preferentially mediated through brain opioid receptors, (c) QNtx antagonizes the immunomodulating activities of Met-Enk and MR 2034, and (d) peripheral opioid systems may also contribute to the immunomodulation evoked by centrally administered kappa-receptor agonist MR 2034. As a whole, this study provides evidence for the involvement of the central opioid system in mechanisms underlying the immune responsiveness.

Species and strain comparisons of immunosuppression by 2-methoxyethanol and 2-methoxyacetic acid

2-Methoxyethanol (ME) and its principal metabolite 2-methoxyacetic acid (MAA) have been shown in our laboratory to be immunosuppressive in male Fischer 344 rats. In this study several strains of 12-week-old female rats and mice were used to compare the immunosuppressive activity of equimolar concentrations of ME and MAA on the trinitrophenyl-lipopolysaccharide (TNP-LPS) antibody plaque-forming cell (PFC) response, which we previously demonstrated to be a sensitive end point. Female inbred Lewis, Fischer 344 and Wistar/Furth, and outbred Sprague-Dawley rats were dosed by gavage with either ME or MAA at dosages of 0.33 to 2.64 mmol/kg/day for 10 consecutive days. Female inbred C3H and C57BL/6J, hybrid B6C3F 1, and outbred CD-1 mice were similarly dosed with equimolar dosages of 0.66 to 5.28 mmol/kg/day ME or MAA. All animals were immunized on day 9 of dosing and PFC responses evaluated 3 days later. Suppression of the PFC response was observed in all strains of rats at 2.64 mmol/kg/day ME or MAA. Lewis and Wistar/Furth rats were found to be the most sensitive strains with suppression at levels as low as 0.66 mmol/kg/day ME or MAA. While ME and MAA dosing resulted in suppression of the TNP PFC response in all the rat strains tested, such treatment did not suppress this PFC response in any of the mouse strains examined. These results indicate that under the conditions of this study rats, but not mice, are immunosuppressed by ME and MAA exposure, and that the susceptibility to immunosuppression differs among rat strains.

Modulation of the in vivo immune response by selective depletion of neutrophils using a monoclonal antibody, RP-3. III. Enhancement by RP-3 treatment of the anti-sheep red blood cell plaque-forming cell response in rats.

Because recent work has shown that neutrophils produce various cytokines and are activated by these agents, this study was undertaken to examine neutrophil participation in immune networks. In our previous work, we demonstrated that delayed type hypersensitivity to SRBC and accompanying mononuclear leukocyte recruitment are inhibited in vivo by selective depletion of neutrophils using a mAb designated RP-3. To elucidate the function of these cells in Ab production, we assessed the splenic plaque-forming cell response to SRBC in a rat model through selective depletion of circulating neutrophils by RP-3. This depletion which occurred at the time of immunization resulted in an increase in the number of anti-SRBC Ab producing cells, as determined by the direct and indirect plaque-forming cell response. This phenomenon was observed only when the Ag was administered i.p. and not with i.v. immunization. These results suggest that neutrophils suppress Ab production in certain situations.

Enhanced Activity of Polynuclear Aromatic Hydrocarbon Mixtures as aryl Hydrocarbon (Ah) Receptor Agonists

Abstract The relative potencies of benzo[a]pyrene and a complex mixture of polycyclic aromatic hydrocarbons (PAH) produced as by-products of manufactured gas plant (MGP) residues as inducers of hepatic microsomal ethoxyresorufin O-deethylase (EROD) were determined in the B6C3F1 mouse. The ED50 values for the induction response were 78 and 65 mg/kg for benzo[a]pyrene and the MGP-PAH mixture, respectively, although benzo[a]pyrene and other compounds containing four or more rings were only trace components of this mixture. A comparison of the EROD induction potencies of benzo[a]pyrene and the MGP-PAH mixture showed that the mixture was approximately 706 times more active than expected based on its benzo[a]pyrene content (0.17%). The enhanced activity of the MGP-PAH mixture was also observed for several other aryl hydrocarbon (Ah) receptor-mediated responses, including inhibition of the splenic plaque-forming cell (PFC) response to both T-cell-dependent and independent antigens in B6C3F1 mice. The nature of t...

Alcohol-Induced Changes in the Immune Response: Immunological Effects of Chronic Ethanol Intake Are Genetically Regulated

Experimental evidence on the immunomodulating effects of ethanol is contradictory and, in animals, the immunological effects of long-term alcohol intake may depend on the age of animal, amount of alcohol consumed, and nutritional composition of the administered diet. In this study, immunological effects of pair-feeding a 35% ethanol-containing Bio-Serv liquid diet for 6 weeks were evaluated using two major histocompatibility complex (MHC)-compatible inbred strains of rats (F344 and LEW). Food intake, rate of gain in body weight, and percentages of B cells, T cells, and T cell subtypes were not affected by ethanol intake. Also, proliferative responses of lymphocytes to T and B cell mitogens were similar in control and ethanol-fed groups of the two strains. Ethanol consumption had no significant influence on spleen weights and the antibody plaque-forming cell (PFC) response in F344 rats; however, in LEW rats, ethanol ingestion leads to a significant decrease (about 16%; p < 0.012) in spleen weight and a > 75% reduction in the PFC response. These results suggest that a non-MHC-encoded gene(s) regulates the ethanol-mediated immunosuppression of the PFC response. Thus, LEW-F344 combination may provide an excellent model to characterize genetic factors which determine sensitivity/resistance to immunological effects of ethanol ingestion.

An immunotoxicity assessment of food flavouring ingredients

A rapid screening protocol incorporating key elements of the US National Toxicology Program's immunotoxicity tier testing strategy was used to evaluate the effects of 35 commonly used food flavouring ingredients on humoral and cell-mediated immune responses. The test compounds were administered intragastrically on a daily basis for 5 days at three dose levels to female CD-1 or B6C3F 1 mice, 6–8 wk old. A host resistance assay ( Listeria monocytogenes bacterial challenge) was conducted to assess cell-mediated immunity. Humoral immunity was measured by the antibody plaque-forming cell (PFC) response to sheep erythrocytes. Body weights, lymphoid organ weights and spleen cellularity were also measured. Cyclophosphamide (80 mg/kg) served as an immunosuppressive positive control agent. The results indicated that the majority of the flavouring ingredients tested did not modulate the cell-mediated or humoral immune response. However, at very high dose levels, two of the materials tested, peppermint oil and citral dimethyl acetal, did increase mortality rate and reduce survival time in the host resistance assay. Neither of these materials significantly altered the PFC response. This rapid, economical screening battery for potential immunotoxicants proved to be a useful means of evaluating a large number of structurally diverse compounds and mixtures to prioritize them for more definitive testing.

Influence of change from grouped to individual housing on a T-cell-dependent immune response in mice: Antagonism by diazepam

Transferring CD-1 mice from grouped to individual housing and then maintaining them individually resulted in a decline in the peak IgM plaque-forming cell (PFC) response to sheep red blood cells (SRBCs). However, the immunosuppression was dependent on the amount of time mice were maintained individually. In particular, individual housing for 5–10 days prior to SRBC inoculation and for 4 days following inoculation resulted in a suppression of the splenic PFC response and serum antibody titers. Shorter periods of individual housing (4 days following inoculation) did not provoke the immunosuppression. Likewise, following more protracted individual housing (15–30 days prior to inoculation) the immunosuppression was not evident. Inasmuch as daily treatment with an anxiolytic, diazepam (1.0 mg/kg), antagonized the suppression induced by 5 days of individual housing, it was suggested that the change from group to individual housing and then maintenance of animals individually acted much like a stressor to induce the immunosuppression.

Evaluation of the effect of low-level 2,3,7,8-tetrachlorodibenzo- p-dioxin exposure on cell mediated immunity

The immunotoxicity of TCDD in the mouse has been well documented. To date, the most sensitive endpoint to TCDD-induced toxicity in mice is that reported by Clark et al. (Clark, D.A., Gauldie, J., Szewczuk M.R. and Sweeney, G. (1981) Proc. Soc. Exper. Biol. Med. 168, 290.) who found that TCDD suppressed the murine cytotoxic T lymphocyte (CTL) response following four weekly doses of 4 ng TCDD/kg/week. However, these results have never been corroborated, as other laboratories have been unable to detect immunosuppression by TCDD at such low levels. In this study, we evaluated the effect of TCDD on the in vivo- and in vitro- generated CTL response to P815 mastocytoma cells in adult C57BL/6J female mice via a 51Cr release assay. Mice were given weekly intraperitoneal injections of TCDD or vehicle for 4 weeks at dosages ranging from 0.01 to 3.00 μg/kg/week. No statistically significant suppression of the in vivo- or in vitro-generated CTL response was detected at any dosage. As expected, significant increases in liver weights and decreases in thymus weights were observed at TCDD dosages of 1.0 and 3.0 μg/kg/week. Likewise, suppression of the antibody plaque forming cell response to sheep erythrocytes was observed at dosages of 1.0 and 3.0 μg TCDD/kg/week. Although expected humoral immunosuppression and organ effects were observed, our data do not support suppression of murine CTL responses at the TCDD doses employed in this study.