Eicosanoids Mediate Manduca sexta Cellular Response to the Fungal Pathogen Beauveria bassiana: A Role for the Lipoxygenase Pathway

摘要

Many studies have documented the involvement of eicosanoids in insect cellular immune responses to bacteria. The use of the fungal pathogen Beauveria basisana as a nodulation elicitor, with inhibition of phospholipase A_2 by dexamethasone, extends the principle to fungi. This study also provides the first evidence of involvement of the lipoxygenase (LOX) pathway rather than the cyclooxygenase (COX) pathway in synthesis of the nodulation mediating eicosanoid (s). The LOX product, 5(S)0hydroperoxyeicosa-6E, 8Z, 11Z, 14Z-tetraenoic acid (5-HPETE), substantially reversed nodulation inhibition caused by dexamethasone and the LOX inhibitors, caffeic acid and esculetin. The COX product, prostaglandin H_2 (PGH_2), did not reverse the nodulation inhibition by dexamethasone or the COX inhibitor, ibuprofen. None of the inhibitors tested had a significant effect on the phagocytosis of B.bassiana blastospores in vitro. Hemocyte phenoloxidase activity was reduced by dexamethasone, esculetin, and the COX inhibitor, indomethacin. The rescue candidates 6-HPETE and PGH_2 did not reverse the inhibition.