Silica induced alterations of murine lymphocyte immunocompetence and suppression of B lymphocyte immunocompetence: a possible mechanism

The alteration of B lymphocyte immunocompetence was studied in the mouse following exposure to silica dust by assaying the thymus independent anti Escherichia coli lipopolysaccharide (LPS) response of mice after immunization with soluble E. coli 055:B5 LPS or with whole E. coli 055:B5. Significant suppression of the cellular and humoral immune response to LPS occurred in the mediastinal lymph nodes which drain the thoracic cavity and in the anatomically distant spleen. Bypassing the silica stressed lung by i.v. injection of Ag resulted in a less severe, but still significant, level of immunosuppression. The suppression was shown not to be due to a shift in the kinetics of the response and it persisted at highly significant levels for up to 3 months after removal of the animals from the exposure chambers. Intraperitoneal injections of filtered silica supernatant fluids from silica suspensions were also able to suppress the LPS response, indicating the involvement of a toxic substance smaller than 0.22 mμ, possibly silicic acid, in the suppression of the B cell response. Serum transfer experiments indicated that a suppressor factor may also be mediating the in vivo B cell suppression observed in silicotic animals.