Structural characterization and immunomodulatory activity of a pectic polysaccharide (CALB-4) from Fructus aurantii

A purified polysaccharide, designated CALB-4, was acquired from Fructus aurantii that is the traditional edible/medicina plant in China. The present study was performed to characterize the CALB-4 and to evaluate its immunomodulatory activities on human peripheral blood mononuclear cells (PBMCs). The structure of CALB-4 was characterized by partial acid hydrolysis, periodate oxidation, Smith degradation, and methylation analysis combined with gas chromatography-mass spectrometry (GC-MS), Infrared Spectroscopy (IR) and scanning electron microscopy (SEM). The results indicated that CALB-4 was elucidated as a pectic polysaccharide and its main chain is composed of Man, Gal UA and Gal, interspersed with Ara, Rha, Man and Gal. Furthermore, immunological tests showed that CALB-4 exhibits the immunoenhancement effects. The mechanism for this action might be attributed to the increase of the cytoplasmic concentration of pro-IL-1 via the up-regulation of several mitogen-activated protein kinases (MAPKs) and the nuclear translocation of p65. This study clarified that CALB-4 could be as an efficacious biological response modifier in immunotherapy.