59 NF-Kappa B Activation and Apoptosis in Lung Neutrophils from Infants with Hyaline Membrane Disease

Abstract

Background: Sequestration and the persistence of neutrophils in the lungs of infants with hyaline membrane disease (HMD) have been associated with pulmonary injury and the subsequent development of chronic lung disease (CLD). While activation of the transcription factor, NF-kappa B, in these cells could upregulate the expression of various mediators that enhance the pulmonary inflammatory process, apoptosis of neutrophils may promote the resolution of lung inflammation. We aimed to determine the proportion of tracheal aspirate samples from infants with HMD that had neutrophils showing evidence of NF-kappa B activation and/or apoptosis.Methods: Tracheal aspirates were collected from mechanically ventilated infants who were diagnosed to have HMD. The cells in the samples were pelleted after centrifugation, fixed and stained for immunofluorescence microscopy. The neutrophils from each sample were stained using anti-p65 antibody to assess for NF-kappa B activation and cleaved caspase-3 antibody for the detection of apoptosis.Results: A total of 172 tracheal aspirates from 59 premature infants were studied. The median gestational age and birthweight were 27 weeks (range, 23 to 36 weeks) and 855 g (range, 500 to 3200 g) respectively. The median age when aspirates were obtained was day four of life and the median number of samples per infant was two. Fifty-four (31%) samples from 33 (56%) infants had neutrophils with evidence of NF-kappa B activation. A total of 68 tracheal aspirates from 27 infants were available for concomitant assessment for neutrophil apoptosis. Eleven (16%) samples from seven (26%) infants showed evidence of neutrophil apoptosis. With the exception of one sample, tracheal aspirates with neutrophils showing NF-kappa B activation or apoptosis were mutually exclusive events.Conclusion: A majority of infants with HMD had indication of a pro-inflammatory milieu in their lungs with tracheal aspirate neutrophils showing activated NF-kappa B. We speculate that NF-kappa B activation in neutrophils may reflect conditions that are anti-apoptotic, and thus be associated with persistent neutrophilic inflammation implicated in the process of lung injury and the development of CLD.