Phospholipase A2 (PLA2) hydrolyzes fatty acids from phospholipids at sn-2 position. Two immune-associated PLA2s are known in Spodoptera exigua. Both are calcium-independent cellular PLA2 (iPLA2A and iPLA2B). These iPLA2s are inducible to immune challenge using different epitopes such as virus, Gram+, Gram- bacteria, and fungi. However, their expression profiles are different between these two iPLA2s. Especially, immune challenge with Gram+ bacteria and fungi significantly up-regulated these iPLA2 expression, suggesting their expression under Toll signal pathway. RNA interferences of Toll or IMD signal components are being investigated.

Chronic/cyclic neutropenia, leukocyte adhesion deficiency syndrome, Papillon-Lefèvre syndrome, and Chédiak-Higashi syndrome are associated with severe periodontitis, suggesting the importance of neutrophils in the maintenance of periodontal health. Various Toll-like receptor (TLR) ligands are known to stimulate neutrophil function, including FcR-mediated phagocytosis. In the present study, the effect of TLR2 activation on the non-opsonic phagocytosis of oral bacteria and concomitant production of reactive oxygen species (ROS) by human neutrophils was evaluated. Neutrophils isolated from peripheral blood were incubated with Streptococcus sanguinis or Porphyromonas gingivalis in the presence of various concentrations of Pam3CSK4, a synthetic TLR2 ligand, and analyzed for phagocytosis and ROS production by flow cytometry and chemiluminescence, respectively. Pam3CSK4 significantly increased the phagocytosis of both bacterial species in a dose-dependent manner. However, the enhancing effect was greater for S. sanguinis than for P. gingivalis. Pam3CSK4 alone induced ROS production in neutrophils and also increased concomitant ROS production induced by bacteria. Interestingly, incubation with P. gingivalis and Pam3CSK4 decreased the amounts of ROS, as compared to Pam3CSK4 alone, indicating the possibility that P. gingivalis survives within neutrophils. However, neutrophils efficiently killed phagocytosed bacteria of both species despite the absence of Pam3CSK4. Although P. gingivalis is poorly phagocytosed even by the TLR2-activated neutrophils, TLR2 activation of neutrophils may help to reduce the colonization of P. gingivalis by efficiently eliminating S. sanguinis , an early colonizer, in subgingival biofilm.

An entomopathogenic fungus Beauveria bassiana (Bb), is a potent pathogen against the beet armyworm, Spodoptera exigua. Phospholipase A2 (PLA2) activities were measured in both immune-associated tissues of hemocytes and fat body S. exigua. Upon the fungal PLA2s were significantly activated in both hemocytes and fat body. Considering inhibitory activity of BZA, we posed a hypothesis that BZA against PLA2 activity of hemocyte, resulting in shutdown of eicosanoid biosynthesis, subsequently inducing immunosupression, which leads to enhance Bb pathogenicity. This study directly analyzed the inhibitory activity of BZA on PLA2 extracted from different immune-related tissues. At low micromolar range, BZA significantly inhibited PLA2s of hemocytes, fat body, and plasma, in which most PLA2 activity was found in hemocytes. Interestingly, an immune signal receptor, Se-Toll, was related with PLA2 activation. RNA interference (RNAi) of Se-Toll significantly inhibited PLA2activity while nonspecific RNAi did not inhibit the PLA2 activity. The RNAi of Se-Toll also significantly suppressed hemocyte nodule response against Bb challenge. In addition, the fungal infection significantly induced activation of PLA2 activity, which would lead to production of immune mediating eicosanoids. This study addressed the synergistic effect of BZA on Bb pathegenicity by its inhibition of PLA2 activity, which was linked with Toll signal pathway.