Further evidence for the involvement of inhibition of cell proliferation and development in thymic and splenic atrophy induced by the peroxisome proliferator perfluoroctanoic acid in mice.

We recently demonstrated that severe thymic and splenic atrophy occur upon dietary treatment of mice with potent peroxisome proliferators (PPs), e.g. perfluorooctanoic acid (PFOA), WY-14,643, nafenopin, and di(2-ethylhexyl)phthalate (DEHP). In the present study, we investigated this phenomenon further employing a relative inert PP, PFOA. Comparison of the dose-dependencies and time-courses indicated that the peroxisome proliferative effect occurred prior to atrophy of both the thymus and spleen. However, following withdrawal of PFOA from the diet, the weight of the thymus and spleen rapidly returned to normal within 10 and 5 days, respectively, in contrast to the more persistent peroxisome proliferation. Furthermore, the changes in thymus and spleen weight upon PFOA treatment and the following withdrawal from diet paralleled the changes in total thymocyte and splenocyte counts, respectively. It was found previously that the decreases in the thymocyte populations present in the S and G2/M phases, as well as in the number of CD4+CD8+ cells upon PFOA treatment, were the most dramatic, perhaps reflecting inhibition of thymocyte proliferation in connection with thymocyte development. Here, the recovery of thymocytes began with increases in the populations in these same phases of the cell cycle, with CD4+CD8+ cells recovering most rapidly, lending further support to our previous hypothesis. The possible relationship of these immunotoxic effects of PPs to the changes they cause in fatty acid metabolism is discussed.