Kerkvliet N I, Oughton J A
College of Veterinary Medicine, Oregon State University, Corvallis 97331.
Toxicol Appl Pharmacol. 1993 Apr;119(2):248-57. doi: 10.1006/taap.1993.1066.
TCDD is a widespread environmental contaminant of concern to human health because of its well-recognized immunotoxicity in laboratory animals. Suppression of the murine antibody response to xenogeneic erythrocytes has been shown to be one of the most sensitive assays for TCDD immunotoxicity. However, the cellular mechanisms underlying the suppressed immune function have not been fully elucidated. In the present studies, peritoneal macrophage recruitment, activation, and antigen-presenting function in response to sheep red blood cell (SRBC) injection were compared in C57Bl/6 mice treated with a single oral dose of 0 or 5 micrograms TCDD/kg. In vehicle-treated mice, SRBC injection induced a typical inflammatory response in the peritoneal cavity. Within 6 hr, the number of neutrophils increased and remained elevated until 40 hr. Macrophage numbers increased at 24 hr and remained elevated through 72 hr. In TCDD-treated mice, a hyperinflammatory response to SRBC was observed. The total number of peritoneal exudate cells was significantly greater at 16, 24, and 40 hr after SRBC challenge when compared to that of vehicle-treated mice. The increased number of peritoneal cells reflected significant increases in both neutrophils and macrophages. Mac-1+ peritoneal cells were examined by two-color flow cytometric analysis on Days 0-3 after SRBC injection for expression of the activation markers F4/80 and I-A. The intensity of F4/80 fluorescence significantly decreased 24-72 hr following SRBC challenge, while fluorescence associated with I-A significantly increased at 72 hr. These changes are consistent with macrophage activation. TCDD did not significantly alter F4/80 expression on Mac-1+ cells, whereas I-A expression was increased earlier on cells from TCDD-treated mice. However, TCDD treatment did not alter the antigen presentation function of peritoneal cells, assessed by their ability to induce the proliferation of SRBC-primed T cells in vitro. The antigen-presenting function of adherent spleen cells was also not altered by TCDD exposure. To test the hypothesis that an excess number of phagocytes in TCDD-treated mice were clearing the antigen more efficiently, leading to a smaller (e.g., suppressed) antibody response, we attempted to overcome TCDD suppression by increasing the amount of SRBC antigen used for challenge. However, the magnitude of the anti-SRBC response in TCDD-treated mice was not significantly altered by increasing the antigen challenge dose, suggesting that enhanced clearance of antigen by macrophage is not a mechanism for TCDD-induced suppression of the anti-SRBC response.(ABSTRACT TRUNCATED AT 400 WORDS)
2,3,7,8-四氯二苯并对二恶英（TCDD）是一种广泛存在的环境污染物，因其在实验动物中具有公认的免疫毒性，故而备受人类健康关注。对异种红细胞的小鼠抗体反应抑制已被证明是TCDD免疫毒性最敏感的检测方法之一。然而，免疫功能受抑制背后的细胞机制尚未完全阐明。在本研究中，对单次口服剂量为0或5微克TCDD/千克的C57Bl/6小鼠，比较了其在注射绵羊红细胞（SRBC）后腹膜巨噬细胞的募集、活化及抗原呈递功能。在用赋形剂处理的小鼠中，注射SRBC诱导了腹膜腔典型的炎症反应。6小时内，中性粒细胞数量增加并持续升高直至40小时。巨噬细胞数量在24小时增加并持续升高至72小时。在TCDD处理的小鼠中，观察到对SRBC的高炎症反应。与赋形剂处理的小鼠相比，SRBC攻击后16、24和40小时腹膜渗出细胞总数显著更多。腹膜细胞数量增加反映了中性粒细胞和巨噬细胞均显著增加。在注射SRBC后0至3天，通过双色流式细胞术分析检测Mac-1+腹膜细胞上活化标志物F4/80和I-A的表达。SRBC攻击后24至72小时，F4/80荧光强度显著降低，而与I-A相关的荧光在72小时显著增加。这些变化与巨噬细胞活化一致。TCDD未显著改变Mac-1+细胞上F4/80的表达，而TCDD处理小鼠细胞上I-A的表达更早增加。然而，TCDD处理未改变腹膜细胞的抗原呈递功能，通过其在体外诱导SRBC致敏T细胞增殖的能力来评估。TCDD暴露也未改变贴壁脾细胞的抗原呈递功能。为了验证TCDD处理小鼠中过量的吞噬细胞更有效地清除抗原从而导致较小（如受抑制）抗体反应这一假说，我们试图通过增加用于攻击的SRBC抗原量来克服TCDD的抑制作用。然而，增加抗原攻击剂量并未显著改变TCDD处理小鼠中抗SRBC反应的强度，这表明巨噬细胞增强的抗原清除不是TCDD诱导抗SRBC反应受抑制的机制。（摘要截短至400字）
