Lipoxin A 4 inhibits Porphyromonas gingivalis - induced aggregation and ROS 1 production - role of neutrophil / platelet interaction and CD 11 b expression

22 Porphyromonas gingivalis is an etiological agent strongly associated with periodontal disease and 23 correlates with numerous inflammatory disorders, such as cardiovascular disease. Circulating 24 bacteria may contribute to atherogenesis by promoting CD11b/CD18-mediated interactions 25 between neutrophils and platelets, causing reactive oxygen species (ROS) production and 26 aggregation. Lipoxin A4 (LXA4) is an endogenous anti-inflammatory and pro-resolving mediator 27 that is protective of inflammatory disorders. The aim of this study was to investigate the effect of 28 LXA4 on the P. gingivalis-induced activation of neutrophils and platelets, and the possible 29 involvement of Rho GTPases and CD11b/CD18 integrins. Platelet/leukocyte aggregation and 30 ROS production was examined by lumi-aggregometry and fluorescence microscopy. Integrin 31 activity was studied by flow cytometry, detecting surface expression of CD11b/CD18 as well as 32 exposure of high affinity integrin epitope, whereas activation of Rac2/Cdc42 was examined using 33 a GST-pulldown assay. The study shows that P. gingivalis activates Rac2 and Cdc42 and up34 regulates CD11b/CD18 and its high affinity epitope on neutrophils, and that these effects are 35 diminished by LXA4. Furthermore, we found that LXA4 significantly inhibits P. gingivalis36 induced aggregation and ROS generation in whole blood. However, in platelet-depleted blood 37 and in isolated neutrophils and platelets, respectively, LXA4 was unable to inhibit either 38 aggregation or ROS production. In conclusion, this study suggests that LXA4 antagonizes P. 39 gingivalis-induced cell activation in a manner that is dependent on leukocyte-platelet interaction, 40 likely via inhibition of Rho GTPase-signalling and down-regulation of CD11b/CD18. These 41 findings may contribute to new strategies in the prevention and treatment of periodontitis-induced 42 inflammatory disorders, such as atherosclerosis. 43 44 on O cber 4, 2017 by gest http/iai.asm .rg/ D ow nladed fom