Effect of short-term inhalation exposure to 1,3-butadiene on murine immune functions.

Interest in 1,3-butadiene (BD) as a potential immunomodulator was prompted by reports of an increased incidence of neoplasia in humans exposed to BD during the manufacture of styrene-butadiene synthetic rubber, and by a recent study which demonstrated a high incidence of thymic lymphomas in B6C3F1 mice. B6C3F1 mice were exposed to 1250 ppm BD by inhalation 6 hr per day, 5 days per week, for 6 or 12 weeks. Immune function assays were selected to evaluate specific humoral and cell-mediated immunity and spontaneous cytotoxicity; lymphoid organ histopathology was also evaluated. A slight decrease in antibody plaque-forming cells (PFC) per spleen was observed in exposed mice, although PFC per 10(6) splenic lymphocytes was normal. Significant extramedullary hematopoiesis and erythroid hyperplasia was observed in spleens from exposed mice, and correlated with a twofold increase in thymidine incorporation in spontaneously proliferating splenocytes. No differences in proliferation to alloantigens were demonstrable between control and BD-exposed splenocytes. Mitogenesis by phytohemagglutinin, Concanavalin A, and lipo polysaccharide was suppressed in splenocytes from exposed mice, but may have been due to the cellular dilution effect of hematopoietic activity. Cytotoxic T-lymphocyte generation was suppressed after a 6-week exposure to BD, but was comparable to controls after 12 weeks of exposure. No differences in spontaneous cytotoxicity were observed between control and exposed mice. Overall, no persistent immunological defects were detectable after inhalation exposure to this tumorigenic agent.