Compartmentalization of the inflammatory response to inhaled grain dust

Interleukin (IL)-1 beta, IL-6, IL-8, tumor necrosis factor (TNF)-alpha, and the secreted form of the IL-l receptor antagonist (sIL-1RA) are involved i n the inflammatory response to inhaled grain dust. Previously, we found con siderable production of these cytokines in the lower respiratory tract of w orkers exposed by inhalation to aqueous extracts of corn dust extract. Alve olar macrophages (AM) have long been considered the cell type responsible f or producing these cytokines, and only recently has it been realized that a irway epithelial cells may also be involved in cytokine production. In orde r to determine whether airway epithelia are involved in the inflammatory re sponse to inhaled corn dust extract and to compare the magnitude of respons e of bronchial epithelial cells (BE) and bronchoalveolar ravage (BAL) cells , we used the reverse transcriptase/polymerase chain reaction (RT/PCR) tech nique in a semiquantitative manner to evaluate the concentration of IL-1 be ta, IL-6, IL-8, TNF-alpha, and sIL-1RA. Alveolar cells were obtained by BAL , and BE were obtained by endobronchial brush biopsy from 15 grain handlers 6 h after experimental inhalation of saline or an aqueous corn dust extrac t. After inhalation of saline, BE expressed low but detectable levels of IL -6, IL-8, and IL-1 beta (> 1 complementary DNA [cDNA] molecule/cell). After inhalation of corn dust extract, the expression of messenger RNA (mRNA) fo r IL-1 beta and IL-8 in the BE were significantly increased, whereas no cha nge was seen in IL-6, sIL-1RA, and TNF-cr mRNA expression. Comparing cytoki ne mRNA levels in BE and BAL cells from the same subjects after inhalation of corn dust extract, BE and BAL cells expressed equivalent amounts of IL-8 mRNA; IL-1 beta was Ii-fold higher in BAL cells; and TNF-alpha and sIL-1RA were expressed exclusively by BAL cells. Immunostaining for the cytokines in BAL cells showed cytokine protein expression in AMs but not in polymorph onuclear cells (PMNs). On the other hand, sIL-1RA was strongly expressed in both AMs and PMNs. Analysis of cytokine protein levels in endobronchial ra vage (EBL) fluid demonstrated that only IL-8 was released in detectable amo unts into the airway lumen, whereas all the other cytokines of interest wer e exclusively found in the BAL fluid. Thus, within 6 h after inhalation exp osure to corn dust extract, BE appear to contribute to airway inflammation by producing IL-8. AMs are responsible for most of the IL-1b and IL-6 produ ction in the alveolar region, whereas AMs and PMNs both produce sIL-1RA. Ou r findings suggest that the inflammatory response to inhaled grain dust is compartmentalized, involving specific mediators of inflammation released by macrophages, neutrophils, and airway epithelial cells.