LFA-1 AND ICAM-1 IN HOMOTYPIC AGGREGATION OF RAT ALVEOLAR MACROPHAGES- ORGANIC DUST-MEDIATED AGGREGATION BY A NONPROTEIN KINASE-C-DEPENDENT PATHWAY

We have examined the role of cell adhesion molecules in the homotypic aggregation of rat alveolar macrophages after exposure to wool and gra in dusts. Molecules such as bacterial lipopolysaccharide (LPS) and pho rbol myristate acetate (PMA) can upregulate adhesion molecules, result ing in aggregation of lymphocytes. In rats treated intratracheally wit h an inspirable sample of wool dust collected from the air of British wool textile mills, and sieved grain dust, aggregates of macrophages w ere present in the bronchoalveolar lavage (BAL). Our hypothesis was th at substances present on the dust surface could activate and upregulat e adhesion molecules of the CD11/CD18 complex on the BAL cells and acc ount for the aggregates. Macrophages from untreated rats form aggregat es in vitro, which averaged 19 cells/aggregate; when treated with both wool and grain dusts, this rose to 25 and 24 cells/aggregate, respect ively. LPS, PMA, and the proinflammatory cytokine tumor necrosis facto r (TNF) also caused increases in aggregate size. Staurosporine, an inh ibitor of protein kinase C (PKC), reduced the number of cells per aggr egate from 35 cells/aggregate in LPS- and PMA-treated macrophages to 1 8 cells/aggregate, the same as untreated. In contrast, staurosporine h ad no effect in reducing the size of aggregates produced by the organi c dusts. Removal of divalent cations, which are essential for maintain ing integrin stability and PKC activity, resulted in complete abolitio n of aggregate formation. Treatment with monoclonal antibodies to lymp hocyte function-associated antigen-1 (LFA-1) alpha and beta and interc ellular adhesion molecule-1 (ICAM-1) resulted in the inhibition of agg regate formation in a dose-dependent manner. Our results strongly sugg est that aggregate formation in response to the two organic dusts invo lves upregulation of adhesion molecules which is not PKC dependent. Th e consequence of these cell interactions in the lungs of workers expos ed to dust in wool textile mills may be important in leading to inflam mation.