Potentiation of murine innate immunity by alpha-galacturonosyl-type glycosphingolipids isolated from Sphingomonas yanoikuyae and S. terrae.

Glycosphingolipids (GSLs) are components of the outer membrane of Sphingomonas species, commonly classified into two types, alpha-glucuronosyl ceramide (alpha-GlcACer) and alpha-galacturonosyl ceramide (alpha-GalACer), respectively. GSL-7 from S. yanoikuyae and GSL-13 from S. terrae, with alpha-GalACer-type structure, possess dihydrosphingosine but with a different ratio of C21cyclopropane to C20:1, while other parts remain similar. We therefore examined if this difference in the ratio of C21cyclopropane to C20:1 in the two ceramides may influence activation of, not only invariant natural killer T (iNKT) cells, but also other cells involved in innate immunity. GSL-7 with a large proportion of C21cyclopropane induced stronger activation of iNKT cells, natural killer cells, dendritic cells, and macrophages than GSL-13 with a large proportion of C20:1. The results show that a higher ratio of C21cyclopropane to C20:1 in the dihydrosphingosine molecule allows a more optimal activation of iNKT cells and other cell types.