A comparison of asbestos and urban particulate matter in the in vitro modification of human alveolar macrophage antigen-presenting cell function.

The mechanism for how inhaled particles cause or exacerbate human diseases is not known. It is clear, however, that some particles are more bioactive than others. One possible mechanism may involve a modification of antigen-presenting cell function. In this study, 2 forms of asbestos (crocidolite and Libby amphibole) and PM(2.5) (an urban particle) were cultured with human alveolar macrophages (HAMs) to determine whether antigen-presenting cell (APC) function was altered. HAMs were exposed to the bioactive particles, asbestos and PM(2.5), for 24 hours, then isolated free of extracellular particulates and nonviable cells. Isolated HAMs were then cultured with autologous lymphocytes in an 11-day APC assay using tetanous toxoid as the antigen and the resulting culture supernatants were assayed for lymphocyte-derived cytokines. Asbestos exposure, regardless of type, up-regulated a TH1 lymphocyte-derived cytokine, interferon gamma (IFNgamma), and the TH2 lymphocyte-derived cytokines interleukin-4 (IL-4) and interleukin-13 (IL-13). PM(2.5) exposure up-regulated all 3 cytokines also. Although cytokine production levels were significantly higher for the treatment compared to control cultures as a group, there was extreme variability in the responses between subjects. In addition, there was no correlation between an individual's cells' response to asbestos verses PM, suggesting that more than one possible mechanism exists for a particle-induced APC effect and individual differential sensitivities to inhaled bioactive particles. This work supports the hypothesis that some inhaled particles can modify immune function by directly affecting APCs thus up-regulating the normal lymphocyte response to antigens in the lung.