The ligand-dependent transcription factor aryl hydrocarbon receptor (AhR) has been implicated in various immune functions. Our previous studies have shown that AhR activation by exposure of ovalbumin (OVA)-immunized mice to the potent ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increases immunization-induced IFN-gamma production in the spleen and suppresses the production of T(h)2 cytokines and OVA-specific antibodies. In the present study, we used transgenic (Tg) mice that express a constitutively active mutant of aryl hydrocarbon receptor (CA-AhR) specifically in T-lineage cells to clarify the role of AhR activation in T cells in these reactions. The results of this study clearly demonstrated that AhR activation only in the T cells augments IFN-gamma production upon OVA immunization. By contrast, production of T(h)2 cytokines and antibodies were not significantly suppressed by CA-AhR in the T cells. These results suggest that suppression of T(h)2 cytokines and antibodies production require AhR activation not only in T cells but also in other cell types as caused by TCDD exposure. Alternatively, these results may indicate that IFN-gamma augmentation and T(h)2 cytokines and antibodies suppression depend on different ways of functions of AhR in the T cells and that CA-AhR does not replicate the suppressive effect of TCDD-activated AhR on T(h)2 cytokines and antibodies. Expression of CA-AhR in the T cells was also shown to increase the percentage of CD25(+) cells among CD4(+) cells in the thymus and spleen. Thus, studies using T-cell-specific CA-AhR Tg mice provide a way to dissect the role of AhR in individual cell types and how the AhR functions.

Our previous study showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure of NC/Nga mice, a mouse model of atopic dermatitis, induces no dermal changes. In the present study, to investigate whether TCDD exacerbates atopic dermatitis-like skin lesions elicited in NC/Nga mice, NC/Nga mice were applied with picryl chloride (PC), and then were exposed to a single oral dose of 0 (control), 5, and 20μgTCDD/kg. Two weeks later, spleens, blood, and skin specimens were collected. TCDD exposure increased the production of Th1-type cytokine IFN-γ, but not Th2-type cytokine IL-4, from spleen cells stimulated with a mitogen. The plasma total IgE antibody levels of the TCDD-exposed mice remained at control levels. On the other hand, TCDD exposure markedly increased the mast cell infiltration and degranulation in PC-sensitized NC/Nga mice histologically, as compared with control mice. These results suggest that TCDD exposure exacerbates atopic dermatitis-related inflammation with no increase of IgE antibody production and that TCDD may be one of the environmental pollutants that induce exacerbations of atopic diseases.

The immune system is one of the organs most vulnerable to the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Among the various immunotoxic effects of TCDD, the thymus involution and suppression of IgM antibody production are well known sensitive reactions of the thymocytes and B cells affected by TCDD. Recently, we reported that TCDD greatly inhibits the production of type-2 helper T (Th2) cell-derived cytokines, especially IL-5, by the splenocytes in mice immunized with ovalbumin (OVA). In the present study, we investigated the dose-dependency of these TCDD immunotoxic effects in OVA-immunized mice to identify the most sensitive target. Mice of two age groups, 6 weeks old and 3 weeks old, were dosed with 0.3, 1.0, or 3.0μg TCDD/kg and immunized with OVA using alum as an adjuvant. Seven days later, the thymus weight, thymocyte population, antigen-specific IgM in the plasma, and IL-5 production by the splenocytes were examined. Among them, IL-5 production was significantly suppressed by all three doses of TCDD and reduced to about 30% by even a small dose of 0.3μg TCDD/kg in both age groups. The thymus weight was significantly reduced by 1.0μg or 3.0μg TCDD/kg, but IgM production was not affected by up to 3.0μg/kg of TCDD in both age groups. Taken together, the Th2 cell-derived IL-5 production was the most sensitive endpoint detecting TCDD toxicity among those examined. Our results also suggest that effector T cells are targets more vulnerable to TCDD toxicity than thymocytes or antibody-producing B cells in the OVA-immunized mice.

The aryl hydrocarbon receptor (AhR) is a transcription factor belonging to the basic helix-loop-helix-PER-ARNT-SIM superfamily. Xenobiotics, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin, bind the receptor and trigger diverse biological reactions. Thymocyte development and T cell-dependent immune reactions are sensitive targets of AhR-dependent 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity. However, the exact role of the AhR in T cells in animals exposed to exogenous ligands has not been clarified because indirect effects of activated AhR in other cell types cannot be excluded. In this study, we generated transgenic (Tg) mice expressing a constitutively active mutant of AhR under the regulation of a T cell-specific CD2 promoter to examine AhR function in T cells. The mRNAs of the constitutively active mutant of AhR and an AhR-induced gene, CYP1A1, were expressed in the thymus and spleen of the Tg mice. The transgene expression was clearly detected in the thymocytes, CD4, and CD8 T cells, but not in the B cells or thymus stromal cells. These Tg mice had a decreased number of thymocytes and an increased percentage of CD8 single-positive thymocytes, but their splenocytes were much less affected. By contrast, the increase in number of T cells and B cells taking place in the spleen after immunization was significantly suppressed in the Tg mice. These results clearly show that AhR activation in the T-lineage cells is directly involved in thymocyte loss and skewed differentiation. They also indicate that AhR activation in T cells and not in B cells suppresses the immunization-induced increase in both T cells and B cells.

Dioxin-like polychlorinated biphenyls (PCBs) exert their toxicities by activating the arylhydrocarbon receptor (AhR), a ligand-dependent transcription factor, in a similar manner to the most toxic dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In the present study, we re-evaluated the relative potency (REP) of the toxic members of dioxin-like PCBs, PCB126 (toxic equivalency factor, TEF 0.1) and PCB169 (TEF 0.01) relative to TCDD, focusing our attention on their effects on the immune reactions of mice immunized with ovalbumin (OVA). Thymus involution, IgM production, and IL-5 produced by the splenocytes were examined in addition to CYP1A1 induction, the established index of AhR-activation, in the spleen. PCB126 had an REP value of 0.1 because of its effects on thymus, IgM, IL-5, and CYP1A1 induction in the spleen, although its effect on IgG1 production was weaker. On the other hand, PCB169 had a smaller REP value estimated at less than 0.01 with regard to CYP1A1 induction in the spleen and all examined immunological effects, except for IgM production. The tissue concentrations of PCB169 and TCDD could not explain the reason for the smaller potency of PCB169, since the spleen contained a higher proportion of PCB169 to TCDD than dosed. These results indicate that dioxin-like PCBs, especially PCB169, shows deviating REPs against immune reactions, and also suggest that PCB169-liganded AhR behaves differently from TCDD-liganded AhR in immune cells.

In the humoral immune response to an invasion of foreign antigens, B cells differentiate into low-affinity antibody-forming cells (AFCs) that mainly secrete IgM or, through germinal center (GC) formation, into high-affinity AFCs that secrete IgG-class antibodies with a higher affinity for the antigen. Previous studies have established the suppressive effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on low-affinity antibody responses to antigens. However, whether and how TCDD affects the high-affinity antibody response to antigens has not yet been clarified. In this paper we investigate the effects of TCDD on GC formation, high-affinity AFC generation, and high-affinity antibody production in the primary humoral immune response. C57BL/6 mice were orally administered 0 or 20 microg/kg of TCDD and subsequently immunized with alum-precipitated ovalbumin (OVA) on day 0. Then the GC formation in the spleen and OVA-specific antibodies in the plasma, was evaluated until day 14 postimmunization. TCDD exposure reduced the production of OVA-specific IgG1 on days 10 and 14. GC formation in the spleen was also suppressed by TCDD exposure, and the suppression persisted from day 7 until day 14. In TCDD-administered mice, on day 7, cellular proliferation in the GCs was significantly suppressed, although apoptosis was not markedly affected. In order to measure high-affinity antibody and high-affinity AFCs, the mice were administered TCDD followed by immunization with alum-precipitated (4-hydroxy-3-nitrophenyl) acetyl linked to chicken gamma-globulin (NP-CG). The frequency of high-affinity NP-specific AFCs that bind to low-haptenated antigen was clearly shown to be reduced in the spleen on days 10 and 14. Furthermore, the high-affinity anti-NP IgG1 levels on days 10 and 14 postimmunization were significantly reduced by TCDD exposure. Taken together, the results of this paper demonstrate that TCDD exposure inhibits the generation of high-affinity AFCs and high-affinity antibody production during the primary humoral immune response and suggest that these alterations were caused by the suppression of antigen-responding B-cell proliferation induced by TCDD during GC formation.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is known to suppress antigen-specific antibody production in humoral immune reactions, but the precise mechanism remains unclear. Since T cell activation and subsequent production of type 2 helper T (Th2) cell-derived cytokines are required for antigen-specific antibody production in humoral immunity, we examined the effects of TCDD on splenic T cell numbers, T cell growth factor IL-2 production, and Th2 cell-derived cytokine production. C57BL/6N mice were orally given TCDD (20 mug/kg) or vehicle, and immediately intraperitoneally immunized with ovalbumin (OVA) adsorbed to alum, and cellular changes in the spleen and cytokine production by spleen cells were investigated from Day 1 to Day 14. In vehicle-control mice the numbers of splenic CD3(+) T cells increased from Day 7 onward, but no increase was observed in the TCDD-exposed mice. When spleen cells from control mice were cultured and restimulated with OVA ex vivo, a significant amount of IL-2 was found from Day 1, but it decreased on Day 7, whereas TCDD exposure promptly suppressed the increase on Day 4. TCDD exposure significantly suppressed the production of Th2 cell-derived cytokines IL-4, IL-5, and IL-6, which were prominently increased from Day 4 onward in control mice. The dose-dependent study showed that IL-5 production was significantly suppressed in a dose-dependent manner starting at 1 mug/kg TCDD. Moreover, separation and reconstitution studies showed that the TCDD-induced suppression of IL-5 production was due to the impaired function of T cells rather than that of antigen-presenting cells. The results of this study suggest that TCDD-induced suppression of T cell activation and Th2-type cytokine production is involved in the impairment of antigen-specific antibody production.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is known to suppress both cellular and humoral immunity. Effector T cell-derived type-2 cytokines, including IL-4 and IL-5, play pivotal roles in humoral immunity. Herein, we studied whether TCDD affects type-2 cytokine productions during the immune response. C57Bl/6 mice were intraperitoneally immunized with ovalbumin (OVA) and orally administered 5 or 20 microg TCDD/kg on Day 0, and then challenged with OVA on Day 21. Seven days later (Day 28), antigen-specific antibodies in plasma, and T cell-derived cytokines produced by splenocytes and proliferation of splenocytes upon ex vivo re-stimulation with OVA were investigated. The quantities of IgM class and IgG1 class OVA-specific antibodies in plasma were reduced by 5 or 20 microg TCDD/kg and by 20 microg TCDD/kg, respectively. While thymus weight and cellularity were reduced by 20 microg TCDD/kg, spleen weight and cellularity were not changed by either 5 or 20 microg TCDD/kg. The proportions of B and T cells in the spleen were not affected by TCDD exposure. On the other hand, splenocytes from mice treated with 5 or 20 microg TCDD/kg were shown to produce less IL-4 or IL-5 upon ex vivo re-stimulation with OVA. Production of the T cell growth factor IL-2 was also decreased in splenocytes from TCDD-treated mice. In contrast, the type-1 cytokine IFN-gamma was increased by TCDD. Twenty micrograms of TCDD/kg suppressed OVA- or T cell mitogen (Con A)-stimulated proliferation of splenocytes, but did not affect B cell mitogen (LPS)-stimulated proliferation. These results suggested compromised T cell activation and suppressed type-2 cytokine production by T cells to be involved in the impaired humoral immunity associated with TCDD exposure.

ADVERTISEMENT RETURN TO ISSUEPREVArticleMicroscopy of Amino Acids and Their Compounds: Silver SaltsKaoru Inouye, Russell Sunderlin, and Paul KirkCite this: Ind. Eng. Chem. Anal. Ed. 1941, 13, 8, 587–588Publication Date (Print):August 1, 1941Publication History Published online1 May 2002Published inissue 1 August 1941https://pubs.acs.org/doi/10.1021/i560096a027https://doi.org/10.1021/i560096a027research-articleACS PublicationsRequest reuse permissionsArticle Views58Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

Of 27 amino acids studied all yielded definite crystalline salts with picrolonic acid. The predominant crystal habit of the picrolonates is acicular, the needles usually being arranged in rosettes. While the appearance of the crystals is thus often insufficiently characteristic, it was found that in nearly all instances the refractive indices can serve for identification of the amino acid.