Submitted on June 5, 2007
Revised on August 1, 2007
TNF-
from Macrophages Enhances LPS-Induced Clara Cell Expression of KC
Arnon Elizur1, Tracy L Adair-Kirk2, Diane G Kelley2, Gail L Griffin2, Daphne E deMello3, and Robert M Senior4*
1 Department of Pediatrics, Division of Allergy and Pulmonary Medicine, Washington University School of Medicine, St louis, MO, USA,
2 Department of Medicine, Division of Pulmonary and Critical Care Medicine, Washington University School of Medicine, St Louis, MO, USA,
3 Department of Pathology, St. Louis University Health Science Center, St Louis, MO, USA,
4 Department of Medicine, Division of Pulmonary and Critical Care Medicine, Washington University School of Medicine, St Louis, MO, USA; Department of Cell Biology and Physiology, Washington University School of Medicine, St Louis, MO, USA
* To whom correspondence should be addressed. E-mail: rsenior{at}im.wustl.edu.
TNF-
is a cytokine produced by alveolar macrophages in response to LPS in the lung. Clara cells are bronchiolar epithelial cells that produce a variety of pro-inflammatory cytokines in response to LPS but not TNF-. In this study, we examined whether TNF- affects Clara cell cytokine production in the setting of LPS stimulation. Using a transformed murine Clara cell line (C22), we observed that both LPS and TNF- induced production of KC and MCP-1. We also found that simultaneous LPS and TNF- stimulation is synergistic for KC production, but additive for MCP-1 production. By using a transwell co-culture system of RAW264.7 macrophages and Clara cells isolated from C57Bl/6 mice, we found that macrophages produce a soluble factor that enhances Clara cell KC production in response to LPS. Co-cultures of Clara cells from mice deficient in TNF- receptors with RAW264.7 macrophages demonstrated that the effect of macrophages on Clara cells is mediated primarily via TNF-. To determine whether these findings occur in vivo, we treated wild type (WT) and TNF receptor-deficient (TNFR-KO) mice intratracheally with LPS and examined the expression of KC. LPS-treated TNFR-KO mice showed much less KC mRNA in airway epithelial cells compared to WT mice. In contrast, a similar number of KC expressing cells was seen in the lung periphery. Thus, up-regulation of KC by Clara cells in the setting of LPS stimulation is largely dependent on TNF- originating from alveolar macrophages. These findings shed light on macrophage-Clara cell interactions in regulating the pulmonary inflammatory response to LPS.
