Relationship between structure and immunological activity of an arabinogalactan from Lycium ruthenicum

An immunologically active arabinogalactan (LRGP3) was selectively degraded by acetolysis, mild acid hydrolysis and enzymatic digestion. After exo-α-l-arabinofuranosidase digestion, 56% of the arabinosyl chains were released. The resistant product (LRGP3-AF) had markedly increased complement fixating activities. The acid hydrolysis product (LRGP3-T) contained (1→3)-linked (17.6%), (1→6)-linked (23.1%), (1→3,6)-linked (30.1%) and terminal (29.2%) galactosyl residues, and its complement fixating activity was lower than that of LRGP3-AF. The side chains (Oligo-S) consisted of arabinose, galactose, and rhamnose in the molar ratios 16.8:1.4:1.0. The complement fixating activity of Oligo-S was weak, but Oligo-S had potent macrophage stimulation activity. Degradation of arabinosyl residues in LRGP3 decreased the macrophage stimulation activity, but the galactan backbone still expressed partial activity. The results demonstrated that the galactan backbone of the polymer might be essential for the expression of complement fixating activity and the arabinosyl side chains could be more responsible for the macrophage activation activity. There may be several structurally different active sites involved in the immunological activity of LRGP3.