ABSTRACT
Bronchopulmonary dysplasia develops in preterm infants due to a combination of lung immaturity and lung injury. Cultured pluripotent bone marrow stem cells (BMSC) are known to reduce injury and induce repair in adult and in immature lungs, possibly through paracrine secretion of soluble factors. The paracrine relationship between BMSC and primary fetal lung epithelial type II cells is unknown. We determined the effects of BMSC on type II cell and fibroblast behavior using an in vitro co-culture model. Rat BMSC were isolated and co-cultured with primary fetal E21 rat type II cells or lung fibroblasts in a Transwell(®) system without direct cell contact. Effects of BMSC conditioned media (CM) on type II cell and fibroblast proliferation and on type II cell surfactant phospholipid (DSPC) synthesis and mRNA expression of surfactant proteins B and C (sftpb and sftpc) were studied. We also determined the effect of fibroblast and type II cell CM on BMSC proliferation and surface marker expression. Co-culture with BMSC significantly decreased type II cell and fibroblast proliferation to 72.5% and 83.7% of controls, respectively. Type II cell DSPC synthesis was significantly increased by 21% and sftpb and sftpc mRNA expressions were significantly induced (2.1 fold and 2.4 fold, respectively). BMSC proliferation was significantly reduced during the co-culture. Flow cytometry confirmed that BMSC retained the expression of undifferentiated stem cell markers despite their exposure to fetal lung cell CM. We conclude that BMSC induce fetal type II cell differentiation through paracrine release of soluble factors. These studies provide clues for how BMSC may act in promoting alveolar repair following injury.
ABSTRACT
INTRODUCTION: CD26 is highly expressed on lung epithelial cells as well as on immune cells. Ovalbumin (OVA)-induced airway inflammation induces a further increase of CD26 expression. CD26-deficient rat strains exhibit blunted clinical courses in models of experimental asthma. OBJECTIVE: (1) To investigate the involvement of regulatory T cells (Tregs) and the surfactant system in a rat model of genetic CD26 deficiency. (2) To investigate regulatory mechanisms dependent on the endogenous CD26 expression. (3) To investigate the impact of CD26 on surfactant protein (SP)-levels under inflammatory conditions. METHODS: Wild-type and CD26-deficient F344 rats were sensitized to and challenged with OVA. Subsequently, airway inflammation, SP levels as well as surface tension of the bronchoalveolar lavage (BAL) fluid were evaluated. RESULTS: CD26 deficiency led to decreased airway inflammation, e.g. reduced numbers of eosinophils and activated T cells in the BAL. Remarkably, the CD26-deficient rats exhibited a significantly increased influx of FoxP3(+) Tregs into the lungs and increased IL-10-secretion/production by draining lymph node cells in culture experiments. Furthermore, in OVA-challenged CD26-deficient rats, the increase of the expression of the collectins SP-A and SP-D as well as of the surface tension-active SP-B was significantly less pronounced than in the CD26-positive strain. Only in the wild-type rats, functional alterations of the surfactant system, e.g. the increased surface tension were obvious after OVA challenge. CONCLUSION: Reduced airway inflammation in CD26-deficient F344 rats appear to be mediated by differences in the recruitment and activity of Tregs. This altered inflammation is associated with differences in the SP expression as well as function.
