Structure, chain conformation, and immunomodulatory activity of the polysaccharide purified from Bacillus Calmette Guerin formulation

•A purified polysaccharide (BDP) was obtained from the injection powder of Bacillus Calmette Guerin formulation.•The primary structure was confirmed and chain conformation of BDP was elucidated.•BDP exhibited significant immunomodulatory activity.

A polysaccharide, coded as BDP, purified from the injection powder of Bacillus Calmette Guerin (BCG) polysaccharide and nucleic acid, was composed mainly of α-D-(1 → 4)-linked glucan with (1 → 6)-linked branches and trace amounts of fucose and mannose from the results of FT-IR, HPAEC-PAD and NMR spectrum. The Mw, Mn, Mz  , and 〈s2〉z1/2〈s2〉z1/2 were determined to be 1.320 × 105 g/mol, 1.012 × 105 g/mol, 2.139 × 105 g/mol, and 21.8 ± 3.2% nm by using HPSEC-MALLS, respectively. The ν   value from 〈s2〉z1/2=KMWν was calculated to be 0.52 ± 0.01, which firstly clarified that BDP existed as random coils in 0.9% NaCl aqueous solution. AFM and SEM combined with Congo-red test also revealed that the polysaccharide was irregular globular like or curly structure. Furthermore, in vitro tests on RAW264.7 murine macrophages cells revealed that BDP exhibited significant immunomodulatory activity.