Miller J S., Stanley D W.
Department of Biological Sciences, Northern Illinois University, 60115, De Kalb, IL, USA
J Insect Physiol. 2001 Dec;47(12):1409-1417. doi: 10.1016/s0022-1910(01)00131-7.
Nodule formation is the quantitatively predominant insect cellular defense reaction to bacterial challenges, responsible for clearing the largest proportion of infecting bacteria from circulation. It has been suggested that eicosanoids mediate several steps in the nodulation process, including formation of hemocyte microaggregates, an early step in the process. While fat body and hemocytes are competent to biosynthesize eicosanoids, the source of the nodulation-mediating eicosanoids remains unclear. To investigate this issue, we studied hemocyte microaggregation reactions to bacterial challenge in vitro. Hemocyte suspensions from the tobacco hornworm, Manduca sexta, were treated with the phospholipase A(2) inhibitor, dexamethasone, then challenged with the bacterium Serratia marcescens. Preparations treated with dexamethasone yielded fewer hemocyte microaggregations than untreated, control preparations. Furthermore, the influence of dexamethasone was reversed by amending experimental (dexamethasone-treated) preparations with the eicosanoid biosynthesis precursor, arachidonic acid. Palmitic acid, which is not a substrate for eicosanoid biosynthesis, did not reverse the influence of dexamethasone on the microaggregation reaction. The influence of dexamethasone was also reversed by adding filtered media from challenged hemocyte preparations to dexamethasone-treated preparations. Finally, most hemocyte preparations treated with selected eicosanoid biosynthesis inhibitors formed fewer hemocyte microaggregations than control preparations. The 5- and 12-lipoxygenase inhibitor, esculetin, did not influence the formation of hemocyte microaggregations in this system. These results are consistent with similar investigations performed in vivo, and we infer that hemocytes are responsible for forming and secreting eicosanoids, which subsequently initiate nodulation by mediating hemocyte microaggregation.
结节形成是昆虫对细菌挑战在数量上占主导的细胞防御反应，负责从循环中清除大部分感染细菌。有人提出，类花生酸在结节形成过程中介导了几个步骤，包括血细胞微聚集体的形成，这是该过程的早期步骤。虽然脂肪体和血细胞能够生物合成类花生酸，但介导结节形成的类花生酸的来源仍不清楚。为了研究这个问题，我们在体外研究了血细胞对细菌挑战的微聚集反应。用磷脂酶A(2)抑制剂地塞米松处理烟草天蛾曼陀罗的血细胞悬液，然后用粘质沙雷氏菌进行挑战。用地塞米松处理的制剂产生的血细胞微聚集比未处理的对照制剂少。此外，通过用类花生酸生物合成前体花生四烯酸改良实验（用地塞米松处理的）制剂，地塞米松的影响被逆转。棕榈酸不是类花生酸生物合成的底物，它不能逆转地塞米松对微聚集反应的影响。将受挑战的血细胞制剂的过滤培养基添加到用地塞米松处理的制剂中，也能逆转地塞米松的影响。最后，大多数用选定的类花生酸生物合成抑制剂处理的血细胞制剂形成的血细胞微聚集比对照制剂少。5-和12-脂氧合酶抑制剂七叶亭在该系统中不影响血细胞微聚集的形成。这些结果与体内进行的类似研究一致，我们推断血细胞负责形成和分泌类花生酸，随后通过介导血细胞微聚集启动结节形成。
