Kocuran, an exopolysaccharide isolated from Kocuria rosea strain BS-1 and evaluation of its in vitro immunosuppression activities

•A new Kocuria rosea BS-1 produced a polysaccharide designated as Kocuran.•It downregulated the release of proinflammatory cytokines in RAW 264.7 macrophages.•Kocuran inhibited the proliferation of PHA-stimulated human PBMC.•Kocuran inhibited complement mediated hemolysis.

In an ongoing survey for bioactive potential of microorganisms from different biosphere zones of India, a promising Kocuria rosea strain BS-1 was identified which produced an exopolysaccharide (designated as Kocuran) exhibiting in vitro antioxidant and immunosuppression properties. Kocuran was characterized as a heteropolysaccharide with repeating monosaccharide residues of glucose, galactose, mannose and glucuronic acid with an average molecular mass of 51.2 kDa. In RAW 264.7 macrophages, Kocuran significantly downregulated the LPS-stimulated ROS, NO, TNF-α, IL-6 and C3 complement component secretion to 4.71 ± 0.08%, 4.11 ± 0.06%, 11.19 ± 0.06 pg ml−1, 9.12 ± 0.07 pg ml−1 and 20.81 ± 0.06 ng/106 cells ml−1, respectively. Furthermore, it inhibited the PHA-stimulated proliferation of human peripheral blood mononuclear cells with IC50 of 100.13 ± 2.1 μg ml−1. In addition, the classical and alternative pathway mediated hemolysis was also inhibited with CH50 and AH50 of 100.96 ± 1.75 and 98.60 ± 1.93 μg ml−1, respectively. Kocuran did not inhibit the LPS-induced LAL enzyme and the binding of FITC-LPS to macrophages suggesting that Kocuran does not neutralize the LPS activity. These results demonstrate the in vitro suppression of activation and macrophage-derived inflammatory cytokines and complement mediated hemolysis indicating its in vitro immunosuppression activity.