A natural sulfated polysaccharide of high molecular weight, a fucoidan isolated from Undaria pinnatifida, is incorporated into Peyer's patches of mice via M cells and induces innate immune responses

Fucoidans (FUs) are sulfated glycans primarily found in marine algae and exhibit various bioactivities. Mekabu FU, from the edible brown alga Undaria pinnatifida, enhances innate and adaptive immunity and exerts protective effects in virus-infected mice, although its mechanisms remain unclear. We aimed to investigate the fate of mekabu FU after oral administration in mice by monitoring the uptake of fluorescence-labeled FU (FL-FU) into Peyer's patches (PPs) through M cells in the intestine and conducting DNA microarray analysis of PPs. FL-FU was observed in M cells 30 min after oral administration in mice. DNA microarray analysis of gene expression in PPs revealed that FU administration altered the expression of genes involved in immune regulation. Orally administered FL-FU was not metabolized into small fragments upon excretion from the mouse intestine, suggesting that mekabu FU suppresses viral infections by modulating intestinal immunity after incorporation into PPs through M cells. • Oral fucoidan assimilates in Peyer's patches (PPs) through M cells in about 30 min • DNA microarray of PPs show control of intestinal immune functions by fucoidan • Oral fucoidan is not metabolized to smaller fragments in the digestive tract