The motor nerve terminal is a novel regulator of anti-ganglioside antibodies in mouse models of autoimmune neuropathy

Autoimmune neuropathies are a group of conditions resulting from inflammatory attack of the peripheral nervous system (PNS). Guillain-Barre syndrome (GBS), an acute autoimmune neuropathy, presents in both axonal and demyelinating forms. Axonal forms of GBS are caused by autoantibodies which target gangliosides on peripheral nerves. Here, they cause axonal damage via activation of the complement pathway. In ex vivo preparations, anti-ganglioside antibodies have been shown to cause complement-mediated injury to the node of Ranvier and the motor nerve terminal. Of these two vulnerable sites, the motor nerve terminal has recently been shown to be able to internalise anti-ganglioside antibody while the node of Ranvier does not. Rabbit models have demonstrated that immunisation with ganglioside results in a motor axonal neuropathy but no such model currently exists in mice. This is partially due to the fact that wildtype mice respond poorly when immunised with ganglioside and partially due to the requirement of an exogenous complement source to cause injury. This laboratory has recently developed GalNAcT-/--Tg(neuronal) and GalNAcT-/--Tg(glial) mice with complex ganglioside expression restricted to neurons and glia, respectively. This thesis aimed to develop a mouse model of GBS by actively immunising these mice with ganglioside liposomes. Subsequently, the aims were expanded to look at the clearance of the antibodies by membranes which express their ganglioside target. To complete these aims, wildtype, GalNAcT-/-, GalNAcT-/--Tg(neuronal) and GalNAcT-/--Tg(glial) mice were compared. Following immunisation with liposomes containing GD1b, wildtype mice responded poorly as demonstrated by low presence of immunoglobulin in their sera. Conversely, GalNAcT-/- mice, which lack complex gangliosides, showed high presence of immunoglobulin in their sera. GalNAcT-/--Tg(neuronal) and GalNAcT-/--Tg(glial) mice showed intermediate levels. This was assumed to be due to varying levels of tolerance to “self” lipids among the mice. However, when normal human serum was introduced, GalNAcT-/--Tg(neuronal) and GalNAcT-/--Tg(glial) mice did not show any complement-mediated injury. Based upon evidence from ELISpots from the splenocytes of these mice, there did not appear to be any major differences in anti-GD1b antibody-producing cells among genotypes. The possibility that the antibodies produced by these mice were being removed by internalisation was investigated at the NMJ ex vivo and in vivo. Ex vivo, antibodies against complex gangliosides were demonstrated to be cleared in a receptor-dependent and activity-dependent manner. Following passive immunisation with pathogenic monoclonal antibody in vivo, serum levels of the antibody were cleared rapidly in wildtype mice but remain elevated at 7 days in GalNAcT-/- mice. GalNAcT-/--Tg(neuronal) mice cleared antibody at an intermediate rate. Non-pathogenic antibodies were not cleared from the circulation over the 7 days from any of the three genotypes. These results have demonstrated that levels of anti-ganglioside antibody can be regulated by receptor-dependent internalisation, especially at the motor nerve terminal. These studies have highlighted this structure as a novel regulator of anti-ganglioside antibody in vivo. The clearance of antibody is also dependent on the ability of the antibody to bind to living tissue; therefore antibodies detected in patient serum may not represent pathogenic, disease-causing antibodies. These factors may profoundly influence host vulnerability to antibody-mediated disease by affecting circulating levels of pathological antibodies.