Immunostimulatory activity and structure of polysaccharide from Streptococcus equi subsp. zooepidemicus.

In the present study, crude capsule polysaccharides from Streptococcus equi subsp. zooepidemicus C55129 (CP) were purified by DEAE cellulose-52 column and Sephadex G-100 column chromatography to afford purified fractions of CP-1, CP-2 and CP-3. The relative molecular weights of CP-1, CP-2 and CP-3 were 29.0, 891.0 and 1338.0 kDa, respectively. CP-1 was composed of mannose, glucose, arabinose and galactose in a percentage ratio of 66.15:28.97:2.43:2.45. CP-2 was composed of mannose, glucose, galactose and glucuronic acid in a percentage ratio of 40.94:27.71:5.96:25.39. In CP-1, there were pyranose rings, α-configuration glycosidic bond residues, one backbone chain (1→6 glycosidic bonds) and two branch chains (1→3 and 1→4 glycosidic bonds) in one repeating unit. In vitro immunostimulatory assay, it was found that CP could promote the splenocyte proliferation and increase the activity of acid phosphatase in peritoneal macrophages. The immunostimulatory activity of CP-1 might be related to its monosaccharide composition, molecular weight and α-configuration glycosidic bond.