MAb10F5 is an Anti-Phospholipid Antibody that Binds in the Basal Ganglia in Vivo

Abstract

IgG2b antibodies are hypothesized to have more anti-phospholipid activity and therefore more likely to enter tissues from the bloodstream. The group A streptococcal conservative M protein sequence when injected into mice generates a promiscuous IgG2b antibody referred to as mAb10F5. Streptococcal antibodies are involved in latent streptococcal disorders including disorders which require movement of antibody into the brain (basal ganglia; caudate/putamen or CPu). Previously, our laboratory demonstrated the binding of streptococcal mAb10F5 with CPu and with liposomes. To determine if mAb10F5 binding to basal ganglia would occur in vivo and if binding with lipids is due to virulence of the antibody or antibody subtype, rats were injected with either control IgG2 antibodies or mAb10F5 and euthanized after 24, 48, or 72 hours. Brains were harvested and immunofluorescence was used to analyze brain slices. Control IgG2 injected rats showed significantly less fluorescence in the CPu than mAb10F5 injected rats at each of the time points (p<0.05). These findings reaffirmed mAb10F5 as an anti-basal ganglia antibody. Fluorescent clouds were visible in slices of brain acquired from mAb10F5 injected rats suggesting entry of the antibody from the bloodstream but not in IgG2 injected controls. To evaluate an anti-phosphopholipid mode of antibody entry, mAb10F5 was examined for anti-phospholipid activity using ELISA. MAb10F5 generated significantly different curves for phosphotidylserine (PS) as compared to phosphotidylinositol (PI) (p<0.05). Though mAb10F5 displayed greater affinity to lipids (PI, PS and cardiolipin were examined) in general when compared to IgG2 controls, mAb10F5 was not significantly different from IgG2b when variation between ELISAs was taken into account. Our findings support mAb10F5 as an anti-basal ganglia antibody in vivo and anti-phospholipid antibody due in part to its own virulence and in part to being an IgG2b subtype.