title: Extracellular DNA: a major proinflammatory component of Pseudomonas aeruginosa biofilms.
abstract: We previously demonstrated that extracellular bacterial DNA activates neutrophils through a CpG- and TLR9-independent mechanism. Biofilms are microbial communities enclosed in a polymeric matrix that play a critical role in the pathogenesis of many infectious diseases. Because extracellular DNA is a key component of biofilms of different bacterial species, the aim of this study was to determine whether it plays a role in the ability of biofilms to induce human neutrophil activation. We found that degradation of matrix extracellular DNA with DNase I markedly reduced the capacity of Pseudomonas aeruginosa biofilms to induce the release of the neutrophil proinflammatory cytokines IL-8 and IL-1beta (>75%); reduced the upregulation of neutrophil activation markers CD18, CD11b, and CD66b (p < 0.001); reduced the number of bacteria phagocytosed per neutrophil contacting the biofilm; and reduced the production of neutrophil extracellular traps. Consistent with these findings, we found that biofilms formed by the lasI rhlI P. aeruginosa mutant strain, exhibiting a very low content of matrix extracellular DNA, displayed a lower capacity to stimulate the release of proinflammatory cytokines by neutrophils, which was not decreased further by DNase I treatment. Together, our findings support that matrix extracellular DNA is a major proinflammatory component of P. aeruginosa biofilms.
authors.affiliation: Departamento de Inmunología, Instituto de Investigaciones Hematológicas and Instituto de Estudios Oncológicos Fundación Maissa, Academia Nacional de Medicina, Buenos Aires, Argentina.
authors.forename: Juan I
authors.initials: JI
authors.lastname: Fuxman Bass
authors.forename: Daniela M
authors.initials: DM
authors.lastname: Russo
authors.forename: Maria L
authors.initials: ML
authors.lastname: Gabelloni
authors.forename: Jorge R
authors.initials: JR
authors.lastname: Geffner
authors.forename: Mirta
authors.initials: M
authors.lastname: Giordano
authors.forename: Mariana
authors.initials: M
authors.lastname: Catalano
authors.forename: Angeles
authors.initials: A
authors.lastname: Zorreguieta
authors.forename: Analía S
authors.initials: AS
authors.lastname: Trevani
mesh_terms: D018441:Biofilms / Q000254:growth & development*; D016207:Cytokines / Q000096:biosynthesis; D004269:DNA, Bacterial / Q000276:immunology*; D045604:Extracellular Fluid / Q000737:chemistry / Q000382:microbiology; D006801:Humans; D018613:Microscopy, Confocal; D018375:Neutrophil Activation / Q000276:immunology*; D009504:Neutrophils / Q000276:immunology* / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000502:physiology*
chemical_list: D016207:Cytokines; D004269:DNA, Bacterial