UREAPLASMA UREALYTICUM INFECTION AND INFLAMMATORY RESPONSES IN MACROPHAGES - THE IMPORTANCE FOR THE DEVELOPMENT AND TREATMENT OF CHRONIC LUNG DISEASE OF PREMATURITY

Li Y-H1, Brauner A1, Yan Z-Q2, Jonsson B1, Skov Jensen J3, Lagercrantz H1, Tullus K1

1Astrid Lindgren Children´s Hospital,2Center for molecular medicine, Karolinska Hospital, Stockholm Sweden, 3SSI, Copenhagen Denmark

 

Objective: Chronic lung disease (CLD) of prematurity is a prolonged respiratory failure in very low birthweight neonates. It is an inflammatory disease of multifactorial etiology. The importance of Ureaplasma urealyticum (UU) in the development of CLD is debated. Steroids produce some improvement in neonates with CLD. Our aim was to study if UU could elicit an inflammatory response in macrophages as a possible mechanism for the induction of CLD.

Methods and Results: A human monocytic cell line (THP-1) differentiated to macrophages, a rat alveolar macrophage cell line (Nr8383), human lung macrophages from TAF in preterm infants and TAF from infants were used. The mRNA expression and protein production of TNF-a, IL-6, VEGF, cell surface and soluble ICAM-1 increased after stimulation with UU measured with RT-PCR, ELISA a specific bioassay and flow cytometry analysis. Dexamethasone, budesonide and to some extent rIL-10 significantly inhibited these inflammatory responses. UU stimulated alveolar macrophages to produce nitric oxide (NO) in a dose and time dependent manner measured by Griese reaction. This effect was further enhanced by IFN-g, but attenuated by steroids. The mRNA and protein levels of inducible NO synthase (iNOS) detected by RT-PCR, Western blot and immunostaining were also induced in response to UU and inhibited by steroids. UU triggered nuclear factor -kB (NF-kB) activation analyzed by electrophoretic mobility shift assay (EMSA) and immunostaining, and this was inhibited by steroids. NO induced by UU caused a 6 fold reduction of its own growth after 10 h.

Conclusions: U. urealyticum may be an important factor in the development of CLD due to its ability to stimulate inflammatory mediators. One important pathway for that seemed to be activation of the transcription factor NF-kB which has been shown to initiate the inflammatory responses in cytokines and NO that we observe. These responses are important defense mechanisms. NO inhibited growth of UU, but are also detriemental to the child. The down-regulatory effect by steroids on NF-kB activation, iNOS expression, production of NO, proinflammatory cytokine, ICAM-1 and growth factor might partly explain the beneficial effect of steroids in neonates with CLD.

 
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