Cellular and biochemical actions of adrenal glucocorticoid hormones on rat thymic lymphocytes

Peroxisome proliferator-activated receptor alpha regulates B lymphocyte development via an indirect pathway in mice

Peroxisome proliferator-activator receptor alpha (PPARalpha), a member of the nuclear receptor superfamily, has been implicated in the regulation of inflammation and immune response. Adaptive immune responses are suppressed by exposure to PPARalpha agonists, resulting in severe thymus and spleen atrophy. In addition, the decline in both T and B cells is due in part to the loss of splenocytes upon exposure to PPARalpha agonists. Thus, the current study was designed to examine the effect of Wy-14,643, a potent PPARalpha agonist, on B cell development in bone marrow from wild-type and PPARalpha-null mice. Significantly decrease in pro/pre-B cell and total B220(+) cell was observed in wild-type mice in bone marrow upon Wy-14,643 treatment, but not in PPARalpha-null mice. Immature and mature B cell populations are not affected. This suggests that PPARalpha is involved in the development of B cell during lymphoid lineage. However, surprisingly, PPARalpha mRNA was absent in bone marrow as revealed by RT-PCR. Therefore, the effect of PPARalpha on B cell development is by an indirect mechanism.

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.

Effects of various inhibitors of oxidative phosphorylation on energy metabolism, macromolecular synthesis and cyclic AMP production in isolated rat thymocytes. A regulating role for the cellular energy state in macromolecular synthesis and cyclic AMP production

Inhibitors of oxidative phosphorylation such as several triorganotin compounds, oligomycin, 2,4-dinitrophenol and carbonylcyanide p-trifluoromethoxyphenylhydrazone suppress energy metabolism of isolated rat thymocytes as indicated by a reduction of ATP levels, an increase in glucose consumption and by a marked accumulation of lactate. Also these compounds effectively inhibit the incorporation of DNA, RNA and protein precursors into acid-precipitable material of thymocytes. Moreover, the prostaglandin E1-induced elevation of cAMP is markedly reduced by these inhibitors. A correlation is observed between the effects on energy metabolism, macromolecular synthesis and cAMP production, since from a series of trialkyltin chlorides, tri-n-propyltin, tri-n-butyltin and tri-n-hexyltin are very effective inhibitors of these functions, while trimethyltin and tri-n-octyltin affect neither of them; other inhibitors of oxidative phosphorylation, each of them with quite different mechanisms of action, also inhibit macromolecular synthesis and cAMP production. The finding that a rise in intracellular ATP concentrations leads to a reversion of the tri-n-butyltin-induced inhibition of cAMP production and uridine incorporation, indicates a regulating role for the cellular energy state in these aspects of cellular function.

Suppression of thymocyte proliferation in vitro by a dioctyltin dichloride-induced serum factor

Oral administration of dioctyltin dichloride (DOTC) results in the production or release of factors which appear to prevent thymocyte maturation at an early stage. Sera obtained from rats gavaged with 75 mg DOTC/kg on alternate days, significantly inhibited PHA-induced blastogenesis of normal thymocytes. In vitro uptake of tritiated thymidine by thymocytes obtained from DOTC-gavaged rats was markedly reduced. These events occurred 24 to 72 h after commencement of DOTC treatment and preceded overt thymic weight loss. The effects of DOTC may therefore be a consequence of factor(s) capable of blocking the intrathymic differentiation of T cell precursors.