Effects of naphthalene and naphthalene metabolites on the in vitro humoral immune response

Abstract

Naphthalene-induced pulmonary and renal toxicity and polycyclic aromatic hydrocarbon-induced carcinogenesis are known to be mediated by their reactive metabolites. Subchronic exposure (90 d) of mice to naphthalene does not alter humoral and cellular-mediated immune responses, whereas polycyclic aromatic hydrocarbons, such as benzo[a]pyrene and 7,12-dimethylbenzanthracene, are known to be immunosuppressive. To understand these differences, the antibody-forming cell (AFC) responses of splenocyte cultures exposed to naphthalene (2, 20, and 200 microM) were evaluated. At these concentrations, the antibody-forming cell response to sheep red blood cells (RBC) was not affected. To determine if reactive metabolites of naphthalene were immunosuppressive, splenocytes were exposed to naphthalene metabolites by direct addition or through the use of a metabolic activation system. The addition of 1-naphthol (70 and 200 microM) and 1,4-naphthoquinone (2, 7, and 20 microM) resulted in a decreased antibody-forming cell response. Suppression of AFC responses was also obtained by culturing splenocytes with liver S9 and naphthalene. Since splenic metabolism of naphthalene to nonimmunosuppressive metabolites may account for the absence of immunotoxicity, the types of naphthalene metabolites generated by splenic microsomes were determined. It was observed that splenic microsomes were unable to generate any detectable naphthalene metabolites, whereas liver microsomes were able to generate both 1,2-naphthalene diol and 1-naphthol. Thus, the absence of an immunosuppressive effect by naphthalene exposure may be related to the inability of splenocytes to metabolize naphthalene. Moreover, the concentration of naphthalene metabolites generated within the liver that may diffuse to the spleen may be inadequate to produce immunotoxicity.