Highlights
Red algal galactans can participate in cell surface biology involving complement system.
Polysaccharides inhibit C3 binding to LPS with direct dependence on degree of sulfation.
Degree of sulfation mattered in carrageenans capacity to reduce C4 binding to mannan.
C4 binding to antibodies was activated in the presence of carrageenans.
No relevant structural characteristics were observed in ameliorating C5 cleavage by plasmin.