Dextran from Leuconostoc mesenteroides augments immunostimulatory effects by the introduction of phosphate groups

The immunological effects of phosphorylated dextran (in which phosphate groups were chemically introduced) on murine splenocytes were examined. When dextran produced by Leuconostoc mesenteroides was phosphorylated by a reaction with polyphosphoric acid in formamide solution for 48 h, the degree of phosphorylation of dextran was maximal. The highest phosphorus content (1.7%, wt/wt) was observed in 40 kDa of dextran. The mitogenic response of murine splenocytes was enhanced by the phosphorylated dextran, but its activity was not related to its molecular weight. A strong response was detected at a concentration of 10 to 500 μg/ml, and the highest activity was obtained 48 h after stimulation. Phosphorylated dextran was characterized as a B-cell-specific mitogen. The expressions of CD86 on CD8α^-CD11c^- and CD8α^-CD11c⁺ cells were augmented by phosphorylated dextran. The levels of mRNA expression of gamma interferon and interleukin-10 on murine splenocytes were also increased by the stimulation. These results demonstrate that dextran exerts immunostimulation by the introduction of phosphate groups.