Purification, structural characterization of an arabinogalactan from green gram (Vigna radiata) and its role in macrophage activation

An acidic arabinogalactan (AGP-2) isolated from green gram Hemicellulose-B was purified using Sephacryl S-
400 and its molecular weight was found to be ∼1200 kDa. Characterization of the AGP-2 by various structural
methods indicated 1,3- β- D- Galactan backbone substituted, at O-6 with 1, 5 linked arabinofuranosyl side
chains, which were further substituted either with mono/di/tri substituted arabinofuranosyl residues resulting in
highly branched structure. Glucuronic acid residues are present as non reducing end terminals. AGP-2 enhanced
the release of NO, TNF- α, IL-6 and IL- 1β and phagocytic capability of macrophages whereas carboxyl reduced
AGP-2 failed to show the similar result indicating the importance of carboxyl groups in macrophage activation.
Pretreatment of macrophages with antibodies specific to extracellular domains of TLR2, TLR4 and TREM1
significantly reduced the AGP-2 induced release of NO and TNF– α indicating the interaction of AGP-2 with TLRs
to activate macrophages.