Immunological consequences of mineral dust inhalation

Our experiments have indicated that in vitro lymphocyte function is a sensitive marker capable of detecting low levels of exposure to mineral dusts. Syngeneic PVG rats were exposed to airborne mineral dusts at a range of mean respirable mass concentrations for periods ranging from two weeks to three months. At predetermined times, splenic lymphocyte function was assessed by measuring the in vitro proliferation response to the mitogens phytohaemagglutinin and concanavalin A. Inhalation of chrysotile A asbestos and quartz had profound but different effects on the immunological status of the rats: chrysotile induced a marked suppression of lymphocyte mitogenic activity, whereas quartz was associated with a marked enhancement of response. In contrast, inhalation of titanium dioxide had no significant effect on lymphocyte reactivity over a wide range of dust concentration. Soluble factors released from lymphoid cells taken from dust exposed rats were capable of inducing immune suppression when transferred to syngeneic naive recipients whereas transfer to normal lymphocyte products had no effect. Moreover, the immunomodulatory effect of intraperitoneal dust inoculation was reduced by pretreatment of rats with cyclophosphamide to inhibit the development of suppressor cell precursors.