A polysaccharide that is alpha-D-Manp-(1->3)-[beta-D-Manp-(1->6)]-beta-D-Manp-(1->4)-beta-D-GlcpNAc-(1->4)-beta-D-GlcpNAc in which a hydroxy group in one of the terminal mannose moieties has been converted into the corresponding Neu5Ac-(1->?)-?-D-Gal-(1->?)-?-D-GlcNAc-(1->?)- glycoside, while two of the hydroxy groups on the other terminal mannose moiety have each been converted into the corresponding Neu5Ac-(1->?)-?-D-Gal-(1->?)-?-D-GlcNAc-(1->?)- glycoside. For the structure shown, either one of the R1 atoms and two of the R2 atoms represent Neu5Ac-(1->?)-?-D-Gal-(1->?)-?-D-GlcNAc-(1->?)- groups or vice versa; the remaining R1 and R2 atoms are hydrogens.