28-Day dietary exposure of mice to a low total dose (7 mg/kg) of perfluorooctanesulfonate (PFOS) alters neither the cellular compositions of the thymus and spleen nor humoral immune responses: does the route of administration play a pivotal role in PFOS-induced immunotoxicity?

Short-term exposure of mice to high doses of perfluorooctanesulfonate (PFOS), an ubiquitous and highly persistent environmental contaminant, induces various metabolic changes and toxic effects, including immunotoxicity. However, extrapolation of these findings to the long-term, low-dose exposures to which humans are subject is highly problematic. In this connection, recent studies have concluded that sub-chronic (28-day) exposure of mice by oral gavage to doses of PFOS that result in serum levels comparable to those found in general human populations suppress adaptive immunity. Because of the potential impact of these findings on environmental research and monitoring, we have examined here whether sub-chronic dietary exposure (a major route of human exposure) to a similarly low-dose of PFOS also suppress adaptive immune responses. Dietary treatment of male B6C3F1 mice for 28 days with a dose of PFOS that resulted in a serum concentration of 11mug/ml (ppm) significantly reduced body weight gain and increased liver mass. However, this treatment did not alter the cellular compositions of the thymus and spleen; the number of splenic cells secreting IgM antibodies against sheep red blood cell (SRBC); serum levels of IgM and IgG antibodies specifically towards SRBC; or circulating levels of IgM antibodies against the T-cell-independent antigen trinitrophenyl conjugated to lipopolysaccharide (TNP-LPS). These findings indicate that such sub-chronic dietary exposure of mice to PFOS resulting in serum levels approximately 8-85-fold greater than those observed in occupationally exposed individuals does not exert adverse effects on adaptive immunity.