Meital Edri-Brami, Inga Shengof, Shirly Tzalik and Rachel G. Lichtenstein
Avram and Stella Goren-Goldstein Department of Biotechnology Engineering, Faculty of Engineering,Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
The N-glycan on Asparagine-297 of the IgG Fc (crystalizeable fragment) is a bi-antennary complex structure that can vary by the addition of sugar residues to the core structure. This glycan is an influential constituent of the IgG antibodies, as it mediates leukocyte activation and inflammation by forming immune complexes through the Fc and the activating Fcγ receptors (FcγRs) on immune cells. Bisecting N-acetylglucosamine, for example increases affinity to FcγIIIRA (CD16), and sialic acid residues reduce affinity to FcγR. Recently, we showed that IgG antibodies derived from ALS patient sera possess bisecting glycan which increases binding of the ALS IgG antibodies to CD16 on effector cell and promoting death of neuronal cells relative to IgG antibodies from healthy volunteers. We further showed over-expression of CD16 and co-localization of intact ALS-IgG antibodies with CD16 and with activated microglia cells in brain and spinal cord of SOD1G93A mice. We hypothesize that motor neuron death in ALS patients is due, in part, to the N-glycans with bisecting and without sialic acid conjugated to the Fc antibodies that accumulated in patient CNS during the disease. Accordingly, in the preliminary study here, we injected recovered Fc-rituximab drug into CSF of 70 days old SOD1G93A mice and characterize the phenotype of the disease. We demonstrated prolonging lives and paralysis reduction of Fc-rituximab-treated females and males of SOD1G93A mice by two to three weeks relative to placebo-treated mice. IgG antibodies of mSOD1 mice bearing the bisecting glycans were further injected into cerebrospinal fluid of pre-symptomatic mSOD1 mice. The injected mice developed the disease two weeks earlier than mSOD1 mice injected by IgG antibodies missing the bisecting glycans and three weeks earlier than mSOD1 mice treated with Fc-Rituximab. Moreover, qRT-PCR revealed CD16 increment in spinal cords of mSOD1 with disease progression and constant low expression in littermates and in brains of mSOD1 mice. We therefore anticipate blocking Fc-CD16 interactions in the CNS by designing inhibitors may prolong patient survival.