Activation of the alternative pathway of complement by an antitumor (1----3)-beta-D-glucan from Alcaligenes faecalis var. myxogenes IFO 13140, and its lower molecular weight and carboxymethylated derivatives.

An antitumor (1----3)-beta-D-glucan with a number-average degree of polymerization (DP) of 540 from Alcaligenes faecalis var. myxogenes IFO 13140, and its lower molecular weight derivatives were found to activate the alternative pathway of complement (APC), as judged by hemolytic and immunoelectrophoretic analyses. Of the native and derivative (1----3)-beta-D-glucans measured, the smallest one that showed APC-activating ability was that with a DP of about 20. The effect of carboxymethylation of the (1----3)-beta-D-glucans with DPs of 49, 131 and 540 on their APC-activating ability was investigated. In any (1----3)-beta-D-glucan the ability was decreased with the increase of carboxymethyl substitution and was completely lost when about one carboxymethyl group per glucose residue was incorporated. In contrast, strong inhibitory ability against C1 hemolytic activity appeared on carboxymethylation.