2007 Volume 30 Issue 11 Pages 2105-2112
In this study, we examined the immunoregulatory roles of L-cycloserine (L-CS), a sphingolipid metabolism regulator with inhibitory activity of serine palmitoyltransferase (SPT), on immune responses mediated by monocytes/macrophages and T cells. Mitogenic responses of splenic lymphocytes induced by LPS, PHA, and Con A were very strongly suppressed by L-CS with IC50 values ranging from 0.5 to 1 μM. In contrast, this compound less strongly blocked IL-2-induced CD8+ CTLL-2 cell proliferation with an IC50 value of 540 μM. Interestingly, L-CS enhanced the number of IL-4-producing helper T cells, indicating the favored induction of Th2 condition. Although tumor necrosis factor (TNF)-α and nitric oxide (NO) production was not altered under 10% FCS condition, U937 cell–cell adhesion as well as the surface level of adhesion molecules (CD29 and CD98) were significantly suppressed by L-CS. In particular, reduced serum level (5%) under L-CS treatment strongly enhanced the production of TNF-α and the inhibitory potency of NO production and cell adhesion. Finally, sphingolipids (D-sphingosine and DL-dihydrosphingosine) did not remarkably abrogate L-CS-mediated T cell proliferation. Therefore our data suggest that de novo sphingolipid metabolism may represent an important aspect of immunomodulatory activities mediated by T cells and macrophages/monocytes, depending on serum level.