Lin Y, Xia L, Turner J D, Zhao X
Department of Animal Science, McGill University, Ste Anne de Bellevue, Quebec, Canada.
Am J Vet Res. 1995 Feb;56(2):203-7.
Neutrophils are present in milk of cows as a means of suppressing invading pathogens during mastitis. However, the manner by which neutrophils traverse the secretory epithelia is still not clear: do they diapedese between epithelial cells or do they kill epithelial cells to gain entry into milk? We investigated the process of bovine neutrophil diapedesis across bovine mammary gland epithelium in vitro. The bovine mammary epithelial cell line MAC-T, grown on collagen-coated filters, formed a confluent monolayer with characteristic tight junctions, basal-apical polarity, and functional barriers to the dye trypan blue. Neutrophils added on the apical surface of the monolayer were stimulated to diapedese across the epithelium by the addition of Staphylococcus aureus (10(7) colony-forming units/ml) to the basal compartment. Light and transmission electron microscopy revealed the series of events for neutrophil transmigration: accumulation of neutrophils on the surface of epithelial monolayer; projection of pseudopods into intercellular junctions and movement of neutrophils between adjacent epithelial cells; and reapproximation of the lateral epithelial cell membranes and reformation of the apical tight junctions after neutrophils crossed the epithelium. Morphologically, epithelial cell damage caused by neutrophil diapedesis was not evident. This in vitro model provides a two-dimensional epithelial sheet by which neutrophil diapedesis can be qualitatively studied under defined conditions. Results of the study suggest a major mode by which bovine neutrophils diapedese across the alveolar epithelia into milk during mastitis.
中性粒细胞存在于奶牛的乳汁中，是乳腺炎期间抑制入侵病原体的一种方式。然而，中性粒细胞穿过分泌上皮的方式仍不清楚：它们是在上皮细胞之间渗出，还是杀死上皮细胞以进入乳汁？我们在体外研究了牛中性粒细胞穿过牛乳腺上皮的渗出过程。在胶原包被的滤器上生长的牛乳腺上皮细胞系MAC-T形成了具有特征性紧密连接、基底-顶端极性以及对台盼蓝具有功能屏障的汇合单层。通过向基底腔室中加入金黄色葡萄球菌（10⁷ 菌落形成单位/毫升），刺激添加到单层顶端表面的中性粒细胞穿过上皮进行渗出。光学显微镜和透射电子显微镜揭示了中性粒细胞迁移的一系列事件：中性粒细胞在上皮单层表面的聚集；伪足向细胞间连接的突出以及中性粒细胞在相邻上皮细胞之间的移动；中性粒细胞穿过上皮后，外侧上皮细胞膜重新靠近并重新形成顶端紧密连接。形态学上，中性粒细胞渗出引起的上皮细胞损伤不明显。这个体外模型提供了一个二维上皮片，通过它可以在确定的条件下对中性粒细胞渗出进行定性研究。研究结果表明了乳腺炎期间牛中性粒细胞穿过肺泡上皮进入乳汁的一种主要方式。
