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.