TNF and leukemia: AOS, such as enzymatically depolymerized guluronate and mannuronate oligomers (enzymatic degradation, degree of polymerization: 20–24, concentration: 500 μg/mL) enhance defense mechanisms against human leukemia cells U937 by upregulating the synthesis cytotoxic cytokines in human mononuclear cells, and these effects are inhibited by antibodies to tumor necrosis factor (TNF) -α [33].