Kraabel B J, Miller M W
Colorado Division of Wildlife, Wildlife Research Center, Fort Collins 80526, USA.
J Wildl Dis. 1997 Jul;33(3):558-66. doi: 10.7589/0090-3558-33.3.558.
We examined the effects of simulated stress on susceptibility of Rocky Mountain bighorn sheep (Ovis canadensis canadensis) neutrophils to Pasteurella haemolytica leukotoxin in a blocked, crossover experiment. Ten captive-raised bighorn sheep were sampled 10 hr after separate administrations of long-acting adrenocorticotrophic hormone (ACTH) gel and normal saline (control). We then compared in vitro leukotoxin-dependent neutrophil death rates after exposure to culture supernatants from four unique P. haemolytica isolates (one from domestic and three from bighorn sheep). Simulated stress effects were evidenced by elevated (P = 0.002) mean plasma cortisol concentrations, more neutrophils (P = 0.037), and fewer lymphocytes and eosinophils (P < or = 0.043) in ACTH-treated bighorn sheep. Maximum leukotoxin-dependent neutrophil death rates were > or = 61% for three of four P. haemolytica isolates tested. For all three cytotoxic isolates, neutrophil death rates at 150 micrograms/50 microliters supernatant were about 1.13 times higher (P = 0.0001) after bighorns received ACTH; for two of these, overall neutrophil death rates were higher (P < or = 0.001) in ACTH-treated bighorn sheep. Although variable leukotoxin production among P. haemolytica strains appeared principally responsible for differences in leukotoxin-dependent neutrophil death rates, susceptibility of bighorn sheep neutrophils to leukotoxin was increased by prior exposure to elevated plasma cortisol concentrations. It follows that if similar processes occur in neutrophils and alveolar macrophages in vivo, they could contribute to greater susceptibility of stressed bighorn sheep to pneumonic pasteurellosis.
在一项区组交叉实验中，我们研究了模拟应激对落基山大角羊（加拿大盘羊指名亚种）中性粒细胞对溶血巴氏杆菌白细胞毒素易感性的影响。十只圈养的大角羊分别接受长效促肾上腺皮质激素（ACTH）凝胶和生理盐水（对照）处理10小时后进行采样。然后，我们比较了暴露于四种独特的溶血巴氏杆菌分离株（一株来自家养动物，三株来自大角羊）的培养上清液后，体外白细胞毒素依赖性中性粒细胞死亡率。ACTH处理的大角羊血浆皮质醇平均浓度升高（P = 0.002）、中性粒细胞增多（P = 0.037）、淋巴细胞和嗜酸性粒细胞减少（P≤0.043），证明了模拟应激效应。在所测试的四种溶血巴氏杆菌分离株中，有三种的最大白细胞毒素依赖性中性粒细胞死亡率≥61%。对于所有三种细胞毒性分离株，大角羊接受ACTH后，150微克/50微升上清液中的中性粒细胞死亡率约高1.13倍（P = 0.0001）；其中两种，ACTH处理的大角羊总体中性粒细胞死亡率更高（P≤0.001）。虽然溶血巴氏杆菌菌株间白细胞毒素产生的差异似乎是白细胞毒素依赖性中性粒细胞死亡率差异的主要原因，但大角羊中性粒细胞对白细胞毒素的易感性因先前暴露于升高的血浆皮质醇浓度而增加。由此可见，如果体内中性粒细胞和肺泡巨噬细胞发生类似过程，可能会导致应激的大角羊对肺炎巴氏杆菌病的易感性增加。
