Plaque-forming Cell Response Research Articles

Carrier-Dependent Suppression of the Anti-phosphorylcholine Plaque-Forming Cell Response inTrichinella-Infected Mice Is Mediated by Anti-hapten IgG1 Antibodies

Baltar, P., Romarı́s, F., Estévez, J., Leiro, J., and Ubeira, F. M. 1998. Carrier-dependent suppression of the anti-phosphorylcholine plaque-forming cell response inTrichinella-infected mice is mediated by anti-hapten IgG1 antibodies.Experimental Parasitology90, 95–102. In normal mice, the phosphorylcholine(PC)-bearingTrichinella spiralisantigen FCp induces PC-specific IgM antibodies. Infection withT. spiralisappears to suppress this response, without affecting the production of anti-PC antibodies in response to other PC-bearing antigens; the suppression can thus be considered carrier-dependent. Previous work in our laboratory has indicated that the observed suppression is due to a soluble factor present in the serum of infected mice. In the work reported here, we investigated the identity of this factor. Afterin vitrostimulation with FCp, spleen cells from FCp-primed infected mice showed a stronger anti-PC IgM response than spleen cells from FCp-primed uninfected mice, confirming that cell memory for FCp is unimpaired by infection. Passive transfer of serum from infected mice to normal recipients, followed by immunization of recipients with FCp or another thymus-dependent or thymus-independent PC-bearing antigen, confirmed that the suppressive agent is soluble and that its activity is carrier-dependent. The suppressive agent was retained by immunoaffinity chromatography with PC or rabbit anti-mouse Ig as ligand, showing that it is a PC-specific Ig. Gel filtration of the fractions retained by PC-immunoaffinity, and subsequent identification of Ig isotypes by an ELISA-based procedure, indicated that the suppressive Igs are of the IgG1 isotype. These findings may be relevant for understanding antibody-mediated down-regulation of the immune response.

Effect of nicotine on the immune system: possible regulation of immune responses by central and peripheral mechanisms.

Nicotine (NT) treatment impairs T-cell receptor (TCR)-mediated signaling, leading to the arrest of T cells in the G1 phase of the cell cycle and inhibition of the antibody plaque-forming cell (AFC) response to sheep red blood cells (SRBC). This paper summarizes some of the previous findings related to cigarette smoke/NT and the immune response, and presents preliminary evidence suggesting that mice chronically treated with NT (0.5 mg/day/kg body weight) have a depressed inflammatory response in the turpentine-induced abscess model of inflammation. This ability of nicotine to attenuate an inflammatory response may also be the cause of reduced mortality of chronically nicotine-treated mice from acute influenza A pneumonitis. Moreover, in LEW rats, decreased anti-SRBC AFC responses were also observed after intracerebroventricular (i.c.v.) administration of relatively small concentrations of NT (28 micrograms/day/kg body weight) which, when given peripherally, did not affect the AFC response. In vitro the addition of NT to T cells increased protein tyrosine kinase (PTK) activity and intracellular Ca2+ concentration [Ca2+]i. These results support the hypothesis that NT alters immune responses by directly interacting with T cells, as well as indirectly through brain-immune interactions.

Requirement of Cytokines for Augmentation of the Antigen-Specific Antibody Responses by Ascorbate in Cultured Murine T-Cell-Depleted Splenocytes

To gain a better understanding of the possible mechanisms by which a stable form of ascorbate, ascorbic acid 2-glucoside (AA-2G), as an ascorbate source, augments antibody responses, we examined whether AA-2G enhances the anti-sheep-red-blood-cell (SRBC) plaque-forming cell (PFC) responses elicited with distinct interleukins that provide signals for B-cell proliferation and differentiation in cultured murine T-cell-depleted splenocytes. The anti-SRBC PFC responses were markedly reduced by T-cell depletion; and additions of the concanavalin A-stimulated murine splenocytes supernatant (CAS) or interleukin (IL)-1β, IL-2, IL-5, IL-4 or IL-6 to the culture limitedly restored the immune responses. AA-2G synergistically stimulated the anti-SRBC PFC responses in the presence of IL-1β-, IL-2, IL-5 or CAS, IL-1β among these cytokines being most highly affected. However, it failed to enhance the PFC responses elicited by IL-4 or IL-6. Repeated additions of ascorbic acid (AsA) during experimental periods could also produced the enhancing effect, but a single addition of the vitamin did not, because of its instability in the medium. It was shown that exposure to IL-1β, IL-2 or IL-5 must be done at early times after antigen stimulation of the cells to support their optimal responses and that AsA exerted its effect on day 2 and day 3 after the start of culture. These results suggest that AsA may up-regulate the in vitro IgM antibody responses in a cytokine-dependent manner.

Evaluation of the potential immunotoxicity of chlorinated drinking water in mice

Recent epidemiological studies have reported associations between the consumption of chlorinated drinking water and various types of human cancer; in addition, exposure to chlorine (Cl −) in drinking water has been reported to suppress certain immune functions in laboratory animals. The current studies were conducted to extend our knowledge of the effects of drinking water exposure to Cl −. Female C57BL/6 mice were administered hyperchlorinated drinking water (7.5, 15, or 30 ppm Cl −) for 2 weeks prior to sacrifice for evaluation of spleen and thymus weights, the plaque-forming cell (PFC) response, hemagglutination (HA) titer, and lymphocyte proliferation (LP). Significant reductions in organ weights and immune response were observed in the positive control groups (i.e. dexamethasone- or cyclophosphamide-exposed mice). No consistent differences were observed between the Cl −-exposed animals and vehicle control mice for the evaluated parameters. Thus, under the conditions of these experiments, 2 weeks of exposure to hyperchlorinated drinking water had no apparent adverse effects on immune function.

Morphine depresses macrophage numbers and function in mouse spleens.

Our laboratory has previously observed that mice implanted with slow-release morphine pellets exhibit profound suppression of their capacity to mount an in vitro antibody response to sheep red blood cells (SRBC) (Bussiere et al., 1992a, b). Suppression was blocked by simultaneous implantation of a naltrexone-releasing pellet, showing that the diminished plaque-forming cell (PFC) responses were mediated via a classical opioid pathway. Although in vitro antibody formation to SRBCs requires the interaction of macrophages, T-cells and B-cells (Fig. 1), macrophages appear to be central to the immu- nosuppressive effect of morphine. Addition of normal splenic macrophages, but not lymphocyte-enriched nonadherent splenocytes, to spleen cell cultures from morphine-pelleted mice restored in vitro antibody production (Bussiere et al., 1993). Further, IL-1, IL-6 and IFN-γ, but not IL-2, IL-4 or IL-5 restored antibody responses of opioid-suppressed cultures (Bussiere et al., 1993). The observation that suppression is reversed by cytokines which are produced by macrophages or which activate macrophages suggests that deficient macrophage function is an important factor in the morphine-induced immunosup- pression. Other evidence that morphine impairs macrophage function in mice includes the decreased ability of colony-stimulating factor-treated bone marrow cells to differentiate into macrophage colonies following morphine treatment in vivo or in vitro (Roy et al., 1991) and the decreased phagocytic capacity (Rojavin et al., 1993; Szabo et al., 1993) of murine peritoneal macrophages presented with the yeast Candida albicans following exposure to morphine or other opioids.

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 log 10 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 log 10 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.

Endpoints for reproductive toxicity

Seasonal hyporesponsiveness and other immune system variations were observed in female B6C3F1 mice during routine screening tests for immunomodulation. In a retrospective assessment, 4 years of data from over 1200 naive, vehicle, and immunosuppressed (cyclophosphamide-treated) control mice were compiled and analyzed for uniformity and significant circannual pattern of immune response. Endpoints included body, spleen, and thymus weights and an immunotoxicity assessment which enumerates specific antibody plaque-forming cells (PFC) in the spleen following immunization with sheep red blood cells. Dosing vehicles were water, corn oil, or 1% methyl cellulose instilled by oral gavage in a 5–20 ml/kg volume once daily for 5 days. Four days later, terminal organ and body weights were recorded and PFC were quantitated. Upon analysis, individual datapoints were arrayed in consistent circannual and seasonal patterns. In naive mice, the yearly peak response in circannual rhythm (acrophase) for body weight and PFC parameters occurred in the summer, with acrophases for spleen and thymus weights located in the spring. Vehicle gavage modulated the circannual/seasonal means and acrophases of all measured endpoints in distinct patterns which varied by vehicle. Body weight was the endpoint least affected by vehicle treatment. Corn oil was the vehicle resulting in the most dramatic effects on natural rhythm. As expected, the naive mice receiving an ip injection of cyclophosphamide exhibited significant decreases (p≤ 0.05) in circannual mean values for PFC response and relative organ weights when compared to naive controls and the elimination of significant expression of rhythm for PFC parameters. Our results indicate that dosing vehicles alter normal seasonal patterns of biological responses in the mouse. These effects on natural rhythms should be considered in toxicity evaluations, especially when comparing datapoints collected at different times of the year.

The effects of perinatal/juvenile methoxychlor exposure on adult rat nervous, immune, and reproductive system function.

In order to address data gaps identified by the NAS report Pesticides in the Diets of Infants and Children, a study was performed using methoxychlor (MXC). Female rats were gavaged with MXC at 0, 5, 50, or 150 mg/kg/day for the week before and the week after birth, whereupon the pups were directly dosed with MXC from postnatal day (pnd) 7. Some dams were killed pnd7 and milk and plasma were assayed for MXC and metabolites. For one cohort of juveniles, treatment stopped at pnd21; a modified functional observational battery was used to assess neurobehavioral changes. Other cohorts of juveniles were dosed until pnd42 and evaluated for changes to the immune system and for reproductive toxicity. Dose-dependent amounts of MXC and metabolites were present in milk and plasma of dams and pups. The high dose of MXC reduced litter size by approximately 17%. Ano-genital distance was unchanged, although vaginal opening was accelerated in all treated groups, and male prepuce separation was delayed at the middle and high doses by 8 and 34 days, respectively. In the neurobehavioral evaluation, high-dose males were more excitable, but other changes were inconsistent and insubstantial. A decrease in the antibody plaque-forming cell response was seen in males only. Adult estrous cyclicity was disrupted at 50 and 150 MXC, doses which also showed reduced rates of pregnancy and delivery. Uterine weights (corrected for pregnancy) were reduced in all treated pregnant females. High-dose males impregnated fewer untreated females; epididymal sperm count and testis weight were reduced at the high, or top two, doses, respectively. All groups of treated females showed uterine dysplasias and less mammary alveolar development; estrous levels of follicle stimulating hormone were lower in all treated groups, and estrus progesterone levels were lower at 50 and 150 MXC, attributed to fewer corpora lutea secondary to ovulation defects. These data collectively show that the primary adult effects of early exposure to MXC are reproductive, show that 5 mg/kg/day is not a NO(A)EL in rats with this exposure paradigm (based on changes in day of vaginal opening, pubertal ovary weights, adult uterine and seminal vesicle weights, and female hormone data) and imply that the sites of action are both central and peripheral.

The influence of vehicle gavage on seasonality of immune system parameters in the B6C3F1 mouse.

Seasonal hyporesponsiveness and other immune system variations were observed in female B6C3F1 mice during routine screening tests for immunomodulation. In a retrospective assessment, 4 years of data from over 1200 naive, vehicle, and immunosuppressed (cyclophosphamide-treated) control mice were compiled and analyzed for uniformity and significant circannual pattern of immune response. Endpoints included body, spleen, and thymus weights and an immunotoxicity assessment which enumerates specific antibody plaque-forming cells (PFC) in the spleen following immunization with sheep red blood cells. Dosing vehicles were water, corn oil, or 1% methyl cellulose instilled by oral gavage in a 5-20 ml/kg volume once daily for 5 days. Four days later, terminal organ and body weights were recorded and PFC were quantitated. Upon analysis, individual datapoints were arrayed in consistent circannual and seasonal patterns. In naive mice, the yearly peak response in circannual rhythm (acrophase) for body weight and PFC parameters occurred in the summer, with acrophases for spleen and thymus weights located in the spring. Vehicle gavage modulated the circannual/seasonal means and acrophases of all measured endpoints in distinct patterns which varied by vehicle. Body weight was the endpoint least affected by vehicle treatment. Corn oil was the vehicle resulting in the most dramatic effects on natural rhythm. As expected, the naive mice receiving an ip injection of cyclophosphamide exhibited significant decreases (p </= 0.05) in circannual mean values for PFC response and relative organ weights when compared to naive controls and the elimination of significant expression of rhythm for PFC parameters. Our results indicate that dosing vehicles alter normal seasonal patterns of biological responses in the mouse. These effects on natural rhythms should be considered in toxicity evaluations, especially when comparing datapoints collected at different times of the year.

Recovery from 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced immunosuppression in A/J mice by treatment with nonsteroidal anti-inflammatory drugs.

We have previously reported that nonsteroidal anti-inflammatory drugs inhibit lung tumorigenesis induced by the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in mice. The aims of this study were to determine if NNK suppresses humoral (i.e., antibody) and cellular immune responses in mice and if nonsteroidal anti-inflammatory drugs could attenuate these immune responses. Female A/J mice (7-8 weeks old) were fed nonsteroidal anti-inflammatory drugs starting 2 weeks before the beginning of NNK treatment (9.1 mg per mouse in total) and continuing through the 7 weeks of NNK treatment. Eight groups (two control groups and six experimental groups) of 10 mice each were used per experiment. Animals in the two control groups received the same diet and water as animals in the six experimental groups; one control group received no nonsteroidal anti-inflammatory drugs or NNK and the other control group received only NNK. The primary humoral and cellular immune responses to the various treatments were assayed by the plaque-forming cell technique and by measurement of natural killer cell cytotoxic activity, respectively. At the end of each experiment, the animals were killed, blood was collected, plasma was prepared, and levels of the immune system modulator prostaglandin E2 were measured. NNK treatment inhibited the plaque-forming cell response by approximately 50%; this inhibition was attenuated by treatment with sulindac or acetylsalicylic acid (P = .0001 for both). In contrast, treatment with naproxen, which had no chemopreventive (i.e., tumor inhibitory) efficacy, further increased by 26% (P = .05) the immunosuppressive effect of NNK. The cytotoxic activity of splenic natural killer cells against YAC-1 cells was reduced by 60% (P = .002); treatment with acetylsalicylic acid (254 mg/kg of diet) reduced the NNK-induced natural killer cell cytotoxicity inhibition by 50% (P = .02), whereas the administration of the specific cyclooxygenase-2 inhibitor NS-398 (7 mg/kg of diet) resulted in an almost complete recovery (approximately 95%, P = .04) of natural killer cell activity. The prostaglandin E2 plasma concentration was approximately 100% greater in NNK-treated mice than in untreated mice. Treatment of the mice with nonsteroidal anti-inflammatory drugs attenuated this elevation (from approximately 25% to 100%), and NS-398 (7 mg/kg of diet) was the most effective (100%). The ability of various nonsteroidal anti-inflammatory drugs to inhibit NNK-induced carcinogenesis appears to be directly related to the ability of these drugs to inhibit NNK-induced immunosuppression. Our results suggest that the chemopreventive effect of nonsteroidal anti-inflammatory drugs may be mediated through the modulation of prostaglandin E2 synthesis.

Opposite effects of 2,2',4,4',5,5'-hexachlorobiphenyl and 2,3,7,8-tetrachlorodibenzo-p-dioxin on the antibody response to sheep erythrocytes in mice.

The effect that cotreatment with 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has on the antibody plaque-forming cell (PFC) response to sheep red blood cells (SRBCs) was determined in female B6C3F1 mice. Groups of eight mice per group were given a single oral dose of PCB153 alone (0, 3.58, 35.8, or 358 mg/kg), TCDD alone (0, 0.1, 1, or 10 micrograms/kg), and all possible combinations of these doses in corn oil 7 days prior to immunization with SRBCs. Separate groups of mice were given phenobarbital (PB) parenterally by intraperitoneal injection at a dosage of 160 mg/kg/day for 3 days. Four days after intravenous immunization, body, spleen, thymus, and liver weights and the PFC response to SRBCs were determined. Exposure to TCDD alone resulted in a dose-related suppression of the PFC response, with significant suppression at 1 and 10 micrograms/kg. In contrast, exposure to PCB153 alone resulted in the enhancement of the PFC response at 358 mg/kg. Combined exposure to 358 mg/ kg PCB153 and TCDD resulted in no change (PCB153 + 0.1 microgram/ kg TCDD) or suppression (PCB153 + 1 or 10 micrograms/kg TCDD) of the PFC response relative to PCB153 alone; however, the PFC response was enhanced (PCB153 + 0.1 microgram/kg TCDD), unaffected (PCB153 + 1 microgram/kg TCDD), or suppressed (PCB153 + 10 micrograms/kg TCDD) relative to corn oil controls. PB did not affect the PFC response to SRBCs, despite a 13-fold induction of hepatic pentoxyresorufin O-dealkylase (PROD) activity. These results suggest that PCB153 enhancement of the PFC response is not related to PROD induction and that it acts as a functional antagonist rather than an aryl hydrocarbon receptor or dispositional antagonist. By enhancing the PFC response to SRBCs, PCB153 raises the "setpoint" response level. Consequently, cotreatment with an immunosuppressive dose of TCDD fails to suppress the PFC response relative to corn oil controls, while clearly suppressing it relative to the appropriate control, PCB153 alone.

Interleukin-2-dependent augmentation of the anti-tnp antibody production by sodium butyrate in cultured murine splenic b cells

Previously we found that sodium butyrate (NaBu) markedly enhanced production of the antibody specific for a T-cell-dependent antigen, sheep red blood cells (SRBC) in murine splenocytes (Kishiro, Y., Ueda, K., Fujiwara, M. and Yamamoto, I., Jpn J. Phamacol., 1994 66, 369–376. To gain a better understanding of the target cells for NaBu's action on antibody responses, we have utilized the T-cell-independent antigen, trinitrophenyl-lypopolysaccharide (TNP-LPS) as a stimulant and have examined an effect of NaBu on the anti-TNP antibody production in vitro. NaBu markedly increased the anti-TNP plaque-forming cell (PFC) responses in murine whole splenocytes, but not in murine splenic B cells. Addition of T-cells or the concanavalin A supernatant (CAS) from murine splenocytes to the B cell cultures completely restored the enhancing effect of NaBu. This effect of CAS was totally blocked by an anti-interleukin (IL)-2 antibody and partially by an anti-IL-lβ or anti-IL-4 antibody. The full enhancing effect of NaBu was also detected when IL-2 was added to the B cell cultures, while IL-2 alone had no stimulatory effect on the control PFC response. IL-lβ alone significantly stimulated the antibody production and adding NaBu to this IL-1β-supplemented culture caused a further increase. Neither IL-4 alone nor NaBu plus IL-4 had any effect on the PFC response. NaBu did not affect the expression of the IL-2 receptor α-and β-chains in B cells stimulated with TNP-LPS. These results suggest that NaBu is an agent that promotes B cell differentiation in vitro in an IL-2-dependent manner.

Immunostimulatory properties of a novel polyphosphoramidate based on stearyl tyrosine

The immunostimulatory property of a synthetic polyphosphoramidate based on stearyl tyrosine (PPST) is described. The immunostimulatory activity of this negatively charged polymer was investigatedin vitro through examining the effect on the mitogen-induced lymphocytes proliferation by a tetrazolium-based colormetric assay and also through studying the primary plaque-forming cells (IgM PFC) responses of Balb/c mice after the intraperitoneal (i.p.) injection of the polymer with sheep red blood cells (SRBC). PPST exhibits specific and high immunostimulatory activityin vitro by the stimulation on lipopolysaccharide(LPS)-induced murine B-cells proliferation, which is probably due to the interaction between the polymer with LPS-responding B lymphocytes. This polymer also makes a significant increase of single antibody producing cells. The result shows that the stimulation rate to IgM PFC response of Balb/c mice achieved 77.9% (p<0.01) when 160 mg/kg of PPST was injected 4 h before with SRBC.

Inhibition of 3,3′,4,4′,5-Pentachlorobiphenyl-induced fetal cleft palate and immunotoxicity in C57BL/6 mice by 2,2′,4,4′,5,5′-hexachlorobiphenyl

3,3′,4,4′,5-Pentachlorobiphenyl (pentaCB) caused a dose-dependent induction of fetal cleft palate in offspring from pregnant C57BL/6 mice exposed to a single dose (783 or 1044 μg/kg) of this compound on gestation and 10. In contrast 2,2′,4,4′,5,5′-hexaCB did not cause cleft palate at a dose 271 mg/kg and, in pregnant mice cotreated with 2,2′,4,4′,5,5′-hexaCB (271 mg/kg) plus 783 or 1044 μg/kg 3,3′,4,4′,5-pentaCB, fetal cleft plane formation was significantly inhibited. 3,3′,4,4′-PentaCB (6 μg/kg) also inhibited the splenic plaque-forming cell (PFC) response and serum IgM levels in C57BL/6 mice treated with the T cell-independent antigen trinitrophenyl-lipopolysaacharide. At doses as high as 72 mg/kg, 2,2′,4,4′,5,5′-hexaCB was not immunotoxic; however, in mice cotreated with a immunotoxic dose of 3,3′,4,4′,5-pentaCB plus different doses of 2,2′,4,4′,5,5′-hexaCB (18, 36 and 72 mg/kg), there was a dose-dependent inhibition of 3,3′,4,4′,5-pentaCB-induced immunotoxicity. These non-additive (antagonistic) interactions of prototypical polychlorinated biphenyl (PCB) congeners may be an important consideration in development of a toxic equivalency factor approach for hazard and risk assessment of PCB mixtures.

Immune responses in an air-breathing teleost Clarius batrachus

The kinetics of the primary and secondary response to a particulate antigen, sheep red blood cells (SRBC), was investigated in terms of antibody-secreting cells by a plaque forming cell (PFC) assay and haemagglutination (HA) tests. Plaque forming cells were found in all the lymphoid organs including the thymus. The antibody response was observed on the second day of immunisation, with a peak PFC response at 5 days after both primary and secondary challenge. Circulating antibodies were detected on the second day by the HA technique with a peak on the 10th day, whereas the peak of the HA titre during the secondary response was attained on the 7th day. The agglutinating antibodies produced after both the first and second injections were 2-mercaptoethanol sensitive, indicating that they are equivalent to the IgM of mammalian species. The cell-mediated immune response in terms of delayed type hypersensitivity reaction was observed with 2,4,-dinitrofluorobenzene (DNFB), a soluble sensitising agent. Maximum induration was observed 72 h after the secondary challenge. In addition, non-specific lytic factors which are characteristic of invertebrates were found in the serum of Clarius batrachusagainst different types of erythrocytes.

Opposite Effects of 2,2′,4,4′,5,5′-Hexachlorobiphenyl and 2,3,7,8-Tetrachlorodibenzo-p-dioxin on the Antibody Response to Sheep Erythrocytes in Mice

The effect that cotreatment with 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has on the antibody plaque-forming cell (PFC) response to sheep red blood cells (SRBCs) was determined in female B6C3F1 mice. Groups of eight mice per group were given a single oral dose of PCB153 alone (0, 3.58, 35.8, or 358 mg/kg), TCDD alone (0, 0.1, 1, or 10 micrograms/kg), and all possible combinations of these doses in corn oil 7 days prior to immunization with SRBCs. Separate groups of mice were given phenobarbital (PB) parenterally by intraperitoneal injection at a dosage of 160 mg/kg/day for 3 days. Four days after intravenous immunization, body, spleen, thymus, and liver weights and the PFC response to SRBCs were determined. Exposure to TCDD alone resulted in a dose-related suppression of the PFC response, with significant suppression at 1 and 10 micrograms/kg. In contrast, exposure to PCB153 alone resulted in the enhancement of the PFC response at 358 mg/kg. Combined exposure to 358 mg/ kg PCB153 and TCDD resulted in no change (PCB153 + 0.1 microgram/ kg TCDD) or suppression (PCB153 + 1 or 10 micrograms/kg TCDD) of the PFC response relative to PCB153 alone; however, the PFC response was enhanced (PCB153 + 0.1 microgram/kg TCDD), unaffected (PCB153 + 1 microgram/kg TCDD), or suppressed (PCB153 + 10 micrograms/kg TCDD) relative to corn oil controls. PB did not affect the PFC response to SRBCs, despite a 13-fold induction of hepatic pentoxyresorufin O-dealkylase (PROD) activity. These results suggest that PCB153 enhancement of the PFC response is not related to PROD induction and that it acts as a functional antagonist rather than an aryl hydrocarbon receptor or dispositional antagonist. By enhancing the PFC response to SRBCs, PCB153 raises the "setpoint" response level. Consequently, cotreatment with an immunosuppressive dose of TCDD fails to suppress the PFC response relative to corn oil controls, while clearly suppressing it relative to the appropriate control, PCB153 alone.

The effect of methyl linoleate hydroperoxides and radical initiator 2,2'-azobis (2-amidinopropane) dihydrochloride on antibody production by mouse spleen cells.

Methyl linoleate hydroperoxides (MLHPO) and 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH), a widely used free radical initiator, were examined for effects on antibody production by spleen cells using plaque-forming cell response against sheep red blood cells (SRBC). The in vitro primary antibody response was enhanced in the presence of MLHPO at a concentration range of 2-20 microM or AAPH at 0.1 microM, but was suppressed with higher concentrations of these compounds. In the in vitro secondary antibody responses, both MLHPO and AAPH failed to increase plaque-forming cell response above that of the control culture. Following the oral administration of MLHPO (2.29 g/kg) four times to mice, in vivo primary plaque-forming cell response was significantly suppressed. After, a single intraperitoneal injection of AAPH (60 mg/kg) to mice, in vitro primary plaque-forming cell response was also suppressed. These findings suggest that primary antibody response can be affected by lipid hydroperoxides and oxygen radicals in vivo.

Influence of Stress on DDT-Induced Humoral Immune Responsiveness in Mice

The effects of different durations/intensities of stress on DDT-induced modulation of humoral immune response were evaluated in mice. DDT (20, 50, or 100 ppm × 4 weeks) per se did not influence the primary antibody response to sheep red blood cells (SRBC). However, when DDT-pretreated mice were exposed to single and multiple sessions of restraint stress (RS), the anti-SRBC antibody titers were lower than the control values, the most prominent effects being seen after 50 and 100 ppm DDT exposure in combination with a single intense stressor (24 hr RS) or repeated stress (1 hr RS × 5). In the splenic plaque forming cells (PFC) assay, similar potentiations of DDT-induced immune suppression were seen at 50 and 100 ppm exposure levels in combination with 24 hr RS or 1 hr RS (×5) procedures. In addition, the 20 ppm DDT exposure effect was also potentiated in combination with the multiple RS model. Further, other forms of stress viz. 3 hr cold restraint stress (CRS) or 6 hr RS, which per se did not influence the antibody titer or PFC response, suppressed humoral immune responses, when combined with 100 ppm DDT exposure. These results are discussed in light of the possible interactions between physical/emotional and environmental/xenobiotic stressors in the regulation of humoral immune response.

Humoral and Cell-Mediated Immune Responses Following Lesions of the Nucleus Basalis Magnocellularis in the Rat

The present study was undertaken to elucidate whether electrolytic lesions of nucleus basalis magno-cellularis–NBM (an animal model of Alzheimer's disease-AD) may influence humoral and cellular immune responses in adult male Wistar rats. For this purpose intact control (IC), sham-operated (SO) and NBM-lesioned rats were divided into two main groups: (1) rats immunized with sheep red blood cells (SRBC) for plaque-forming cell (PFC) response and anti-SRBC agglutinins, and (2) rats immunized with bovine serum albumin in complete Freund's adjuvant (BSA-CFA) for anti-BSA antibody production, Arthus and delayed hypersensitivity skin reaction to BSA. PFC responses and anti-SRBC agglutinins as well as diameter and expression of edema/induration of Arthus/delayed skin reaction and titer of anti-BSA antibody were significantly lower in NBM lesioned rats (compared to IC and SO). The results showed that in NBM-lesioned rats both the humoral and cellular immune responses were suppressed.