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

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.