Water soluble phosphorylated β-1→3-D-glucan (GP) was prepared as done before [20]. The physicochemical characteristics of GP were determined as reported previously [20,26]. GP was dissolved in aqueous media, filter-sterilized (0.2 μm) and screened for endotoxin contamination with the Endospecy assay (Seigakaku, Tokyo, Japan), which is specific for endotoxin but does not respond to β-1→3-D-glucans.