Differential Expression of Interleukin 1 Alpha by Thy-1+ and Thy-1- Lung Fibroblast Subpopulations: Enhancement of Interleukin 1 Alpha Production by Tumor Necrosis Factor-alpha

The purpose of this investigation was to determine whether subpopulations of murine lung fibroblasts produced interleukin 1 (IL 1). We previously identified two major populations of pulmonary fibroblasts based on the presence or absence of Thy-1. Thy-1+ and Thy-1- subsets synthesize fibronectin and type I and III collagen, but only the Thy-1- population displays class II major histocompatibility complex antigens after stimulation with interferon-gamma and presents antigen to T helper clones. Interestingly, in the current study we determined that only Thy-1- fibroblast lines and clones synthesized IL 1. Although constitutive production was low, tumor necrosis factor -alpha (TNF-alpha) stimulated 5-20-fold increases in IL 1 production in Thy-1- fibroblasts. The Thy-1+ fibroblasts did not produce IL 1 even after TNF-alpha treatment. Northern blot analysis of TNF-alpha treated cells revealed that in the Thy-1- subset increased mRNA levels for IL 1 alpha were detected, while IL 1 beta mRNA was not detected. Furthermore, IL 1 activity from TNF-alpha-treated Thy-1- fibroblast membranes and supernatants was completely neutralized by IL 1 alpha-specific antibodies. These observations support the hypothesis that the antigen-presenting Thy-1- subset is important for promoting the inflammation associated with pulmonary fibrosis. In addition, the existence of functional subsets of lung fibroblasts is further substantiated by differential expression of IL 1.