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.