In vitro depression of human lymphocyte mitogen response (phytohaemagglutinin) by asbestos fibres.

Asbestosis is a fibrotic lung disease associated with chronic inhalation of asbestos dust. The response of peripheral blood mononuclear cells (PBM) to phytohaemagglutinin (PHA) in asbestosis patients has been reported to be impaired, suggesting a disturbance in the cell-mediated response of chronically exposed individuals. We demonstrated that PHA responses of normal PBM are also depressed when exposed to various forms of asbestos fibres in vitro. Furthermore, we showed the primary effect of the fibres to be on lymphoid (non-adherent) populations rather than monocytes (adherent cells). Exposure as brief as 1 hr affected the subsequent PHA response of the cells. This effect did not appear to involve suppressor cell activation nor was it mediated by soluble factors. Our findings therefore offer an explanation for the alterations in the cellular immune response observed in humans as a result of lymphoid cells coming into transient contact with inhaled asbestos fibres residing in the lung.