The S1P1 receptor antagonist W146 induces lymphopenia in mice. Demonstration that functional antagonism of S1P1 is the mechanism of lymphopenia evoked by fingolimod-like compounds. (140.15)

Abstract

Abstract Agonists of sphingosine 1-phosphate receptor 1 (S1P1) are a novel class of immunosuppressants. S1P is the endogenous agonist of S1P1 and promotes lymphocyte egress from lymph nodes (LN) into blood. However, synthetic agonists like fingolimod prevent the egress, causing systemic lymphopenia. This apparent contradiction is explained by the concept of functional antagonism, according to which synthetic S1P1 agonists induce receptor internalization, making cells unresponsive to the endogenous S1P. If this mechanism is true, S1P1 antagonists should induce lymphopenia. We have fully characterized compound W146, a S1P1 antagonist, by binding and cellular assays. We then administered W146 and several S1P1 agonists to mice and measured blood lymphocytes and plasma levels of compounds in different experimental conditions. All compounds induced lymphopenia in blood and a concomitant increase of CD4+ and CD8+ T cells in LN. These results indicated that lymphopenia evoked by W146 was due to S1P1 blockade and not to another mechanism, like cytotoxicity. By Western blot, FACS and immunocytochemistry we showed that all compounds but W146 induce S1P1 internalization. W146 is able to prevent the internalization induced by an agonist. We report, for the first time, lymphopenia with a S1P1 antagonist. Plasma levels needed to surmount the effects of endogenous S1P are achieved in our experimental conditions. Our studies strongly support the validity of the concept of functional antagonism.