Macrophage immunomodulatory activity of extracellular polysaccharide (PEP) of Antarctic bacterium Pseudoaltermonas sp.S-5

Antarctic bacteria are a novel source of polysaccharides which might have potential applications as biological response modifiers (BRM). A heteropolysaccharide (PEP) was isolated from the liquid culture broth of the Antarctic bacterium Pseudoaltermonas sp.S-5. PEP contained Mannose, Glucose, and Galactose in a ratio of 4.8:50.9:44.3. High performance gel permeation chromatography of this polysaccharide showed a unimodal profile, and the molecular weight was 397 kDa. PEP was studied for its immunological effects on peritoneal macrophage cells. Morphological alterations were observed in macrophages treated with PEP. In vitro exposure to PEP increased the occurrence of activated macrophages and endocytic index in a dose-dependent pattern (2.5-50 μg/ml) after 24 h of incubation, since increase of 136% and 133% was detected in the activated macrophage percentage and endocytic index respectively compared to untreated cells. At 200 μg/ml PEP caused a greatest increase (44.5%) in NO production when compared to the control group; however, this polysaccharide did not affect respiratory burst in the absence of PMA. Furthermore, it was demonstrated that PEP induces macrophages to secrete tumor necrosis factor (TNF)-α and interleukin (IL)-1β. These results suggested that PEP from Pseudoaltermonas sp.S-5 can be classified as a BRM.