A Haemophilus influenzae strain associated with Fisher syndrome expresses a novel disialylated ganglioside mimic

The non-typeable Haemophilus influenzae strain DH1 was isolated from a 25 year old male patient with Fisher syndrome, a postinfectious autoimmune condition characterized by the presence of anti-GQ1b IgG antibodies that target and initiate damage to peripheral nerves. DH1 was found to display an alphaNeuAc(2-8)alphaNeuAc(2-3)betaGal branch bound to the tetraheptosyl backbone core of its lipooligosaccharide (LOS). The novel sialylation pattern was found to be dependent on the activity of a bifunctional sialyltransferase, Lic3B, which catalyzes the addition of both the terminal and subterminal sialic acid residues. Patient serum IgGs bind to DH1 LOS, and the reactivity is significantly influenced by the presence of sialylated glycoforms. The display by DH1, of a surface glycan that mimics the terminal trisaccharide portion of disialosyl-containing gangliosides, provides strong evidence for its involvement in the development of Fisher syndrome.