SumnlagyDendritic cells (DC) are widely distributed in the lung where they are distinguished by their morphology and class II major histocompatibility complex (Ia) antigen expression. Although a role for DC as pulmonary antigen-presenting cell (APC) has been suggested, little is currently known concerning how these ceils respond to inhaled antigens in vivo. Hen-egg lysozyme (HEL) was injected intratracheally into Lewis rats; DC were subsequently purified from the lung and regional lymph nodes (LN) at intervals of up to 14 d and examined for their ability to stimulate the proliferation of HEL-immune T calls in vitro in the absence of added HEL. Pulmonary DC displayed APC activities at 3 h and for up to 7 d after the injection of antigen. Dendritic cells in the draining hilar LN showed APC activities that appeared at 24 h, peaked at day 3, and then diminished progressively. After the primary sensitization, HEL-immune T ceils were detected in hilar LN but not in the lung. A second airway challenge with HEL at day 14 yielded an antigen-specific pulmonary immune response, characterized histologically by the accumulation of mononuclear calls around lung venules. We conclude that APC activities shift from lung to lymph node during the response to inhaled antigen.

Dendritic cells are specifically adapted to provide accessory signals for the growth of T lymphocytes. Ia+ dendritic cells are present within the normal lung; however, little is known concerning their regulation in vivo. Interferon-gamma (IFN-gamma) is a proinflammatory lymphokine that augments the expression of Ia antigens and promotes the accessory activities of a variety of cells. In order to determine whether IFN-gamma regulates pulmonary dendritic cells in vivo, Lewis rats were injected intraperitoneally with recombinant murine IFN-gamma (2 x 10(5) U/rat/day) or with buffered saline for 5 consecutive days. Following sacrifice, the lungs were excised, and the distribution and number of Ia (OX-6)+ cells was determined in situ. Dendritic cells were localized in the mucosal lining of the tracheobronchial tree, in pulmonary capillaries, as well as in the alveolar septal interstitium and subjacent to the pleural surfaces. IFN-gamma yielded a specific increase in Ia+ dendritic cells in alveolar septa and in pulmonary airways. Purified Ia+ dendritic cells from enzymatic digests of lung were excellent accessory cells for the proliferative responses of both antigen-primed and naive T lymphocytes. IFN-gamma did not, however, further augment the expression of Ia antigens or the accessory activities of pulmonary dendritic cells. These results suggest that IFN-gamma may promote pulmonary T cell-mediated inflammatory responses in vivo by increasing the number of Ia+ dendritic accessory cells in the lung.

The pathogenesis of asbestos-induced pleural fibrosis is poorly understood. Moreover, there has been a long-standing controversy regarding the relative potential of different commercial types of asbestos to cause pleural disease. We postulated that inhaled asbestos fibers translocate to the pleural space where they stimulate the recruitment and activation of pleural macrophages. To test this hypothesis, and to determine whether there are differences between inhaled amphibole and serpentine asbestos, Fischer 344 rats were exposed by intermittent inhalation (6 hr/day for 5 days/week over 2 weeks) to either National Institute of Environmental Health Sciences (NIEHS) crocidolite (average concentration 7.55 mg/m3) or NIEHS chrysotile fibers (average concentration 8.51 mg/m3). Comparisons were made with sham-exposed rats. The rats were sacrificed at 1 and 6 weeks after the cessation of exposure. More pleural macrophages were recovered at 1 and 6 weeks after crocidolite and chrysotile exposure than after sham exposure. Small numbers of crocidolite fibers (approximately 1 per 4000 cells) were detected in the pleural cell pellet of one crocidolite-exposed rat by scanning electron microscopy. Pleural macrophage supernatants were assayed for production of nitric oxide (NO) (by the Griess reaction) and tumor necrosis factor alpha (TNF-x) (by an enzyme-linked immunosorbent assay method). Significantly greater amounts of NO as well as TNF-a were generated by pleural macrophages at 1 and 6 weeks after either crocidolite or chrysotile inhalation than after sham exposure. Conceivably, translocation of asbestos fibers to the pleural space may provide a stimulus for persistent pleural space inflammation, cytokine production, and the generation of toxic oxygen and nitrogen radicals. Enhanced cytokine secretion within the pleural space may in turn upregulate adhesion molecule expression and the synthesis of extracellular matrix constituents by pleural mesothelial cells. Thus, our findings may have significance for the development of asbestos-induced pleural injury.

The pathogenesis of asbestos-induced pleural fibrosis is poorly understood. Moreover, there has been a long-standing controversy regarding the relative potential of different commercial types of asbestos to cause pleural disease. We postulated that inhaled asbestos fibers translocate to the pleural space where they stimulate the recruitment and activation of pleural macrophages. To test this hypothesis, and to determine whether there are differences between inhaled amphibole and serpentine asbestos, Fischer 344 rats were exposed by intermittent inhalation (6 hr/day for 5 days/week over 2 weeks) to either National Institute of Environmental Health Sciences (NIEHS) crocidolite (average concentration 7.55 mg/m3) or NIEHS chrysotile fibers (average concentration 8.51 mg/m3). Comparisons were made with sham-exposed rats. The rats were sacrificed at 1 and 6 weeks after the cessation of exposure. More pleural macrophages were recovered at 1 and 6 weeks after crocidolite and chrysotile exposure than after sham exposure. Small numbers of crocidolite fibers (approximately 1 per 4000 cells) were detected in the pleural cell pellet of one crocidolite-exposed rat by scanning electron microscopy. Pleural macrophage supernatants were assayed for production of nitric oxide (NO) (by the Griess reaction) and tumor necrosis factor alpha (TNF-alpha) (by an enzyme-linked immunosorbent assay method). Significantly greater amounts of NO as well as TNF-alpha were generated by pleural macrophages at 1 and 6 weeks after either crocidolite or chrysotile inhalation than after sham exposure. Conceivably, translocation of asbestos fibers to the pleural space may provide a stimulus for persistent pleural space inflammation, cytokine production, and the generation of toxic oxygen and nitrogen radicals. Enhanced cytokine secretion within the pleural space may in turn upregulate adhesion molecule expression and the synthesis of extracellular matrix constituents by pleural mesothelial cells. Thus, our findings may have significance for the development of asbestos-induced pleural injury.

In earlier studies, we had determined that class II (Ia) major histocompatibility complex (MHC) antigen expression in the normal rat lung was limited to dendritic cells and type II alveolar cells. In order to characterize the Ia+ pulmonary dendritic cells of the lung parenchyma, Lewis rat lungs were dissected free of their major airways, enzymatically digested, and serially subjected to density centrifugation on bovine serum albumin, overnight adherence, and immunopanning with a murine anti-rat monoclonal antibody (anti-OX-6) that reacts specifically with class II (Ia) MHC antigens. The purified Ia+ pulmonary cells displayed the morphologic and functional features of dendritic accessory cells, including extended cell processes, absence of nonspecific esterase staining, minimal phagocytosis of latex beads, rapid clustering with T lymphocytes, and co-stimulation of T-cell mitogen responses. Detailed immunophenotyping by cytofluorimetry and immunohistology showed that the purified dendritic cells were Ia (OX-6)+, CD45R (OX-1)+, CD45Rb (OX-22)-, ICAM-1+, and OX-43-. As many as 50% of the cells bound heat-aggregated IgG, while a smaller percentage expressed the CD43 sialophorin antigens (W3/13) expressed by a variety of blood-derived cells, and/or the OX-41 and RMA macrophage antigens. We conclude that Ia+ dendritic cells of lung are heterogeneous with respect to their expression of surface membrane differentiation antigens and may prove to be functionally distinct with respect to their accessory activities.