Potentiation of a functional autoantibody in narcolepsy by a cholinesterase inhibitor.

We have recently reported the presence of an immunoglobulin G (IgG) autoantibody (Ab) in patients with narcolepsy with cataplexy that abolishes spontaneous colonic migrating motor complexes (CMMCs) and increases smooth muscle tension and atropine-sensitive phasic contractions in a physiological assay of an isolated colon. In this study, we used the cholinesterase inhibitor, neostigmine, to explore the mechanism of the narcoleptic IgG-mediated disruption of enteric motor function in four patients with narcolepsy with cataplexy and to identify a pharmacological mimic of the Ab. Neostigmine potentiated the narcoleptic IgG-mediated increase in smooth muscle resting tension and phasic smooth muscle contractions by an atropine-sensitive mechanism but exerted no effect on resting tension in the presence of control IgG. Decreased frequency of CMMCs mediated by IgG with anti-M3R activity was reversed by neostigmine. Therefore, a challenge with a cholinesterase inhibitor improves the specificity of the CMMC assay for narcoleptic IgG. Tetrodotoxin (TTX), a neuronal sodium channel blocker, also abolished CMMCs and increased resting tone, and a similar potentiation was observed with neostigmine; thus, TTX is a mimic of the functional effects of the narcoleptic IgG in this bioassay. These findings provide a link to pharmacological studies of canine narcolepsy and are consistent with a functional blockade of both excitatory and inhibitory motor neurons by the narcoleptic Ab, similar to the TTX mimic, presumably by binding to an autoantigenic target expressed in both populations of neurons.

An autoantibody in narcolepsy disrupts colonic migrating motor complexes.

Despite strong circumstantial evidence for the autoimmune hypothesis of narcolepsy, conventional immunological methods have failed to detect an autoantibody. This study investigated the real-time effects of narcoleptic immunoglobulins on a spontaneous colonic migrating motor complex (CMMC) preparation. IgG from patients with narcolepsy with cataplexy or healthy controls was added directly to isolated mouse colons undergoing CMMC activity to test for autoantibodies that disrupt colonic motility. The effect of immunoglobulins prepared for clinical intravenous treatment (IVIg) on autoantibody-mediated colonic disruption was also assessed. Narcoleptic IgGs markedly reduced the frequency of CMMCs or irreversibly abolished them. Abrogation of CMMCs was followed by an increase in the resting tension of the colon preparation and appearance of atropine-sensitive phasic smooth muscle contractions. IVIg partially neutralized the inhibitory effect of narcoleptic IgG on the CMMCs. The dramatic effect of narcoleptic IgG on CMMC generation is consistent with an autoantibody-mediated disruption of enteric neural pathways. The ex vivo whole-organ approach allows real-time examination of the physiological effects of the narcoleptic autoantibody and offers a new avenue for exploring the autoimmune basis of narcolepsy. The neutralizing effect of IVIg on the autoantibody provides a rationale for the reported clinical improvement in cataplexy when IVIg are given at disease onset.

A functional autoantibody in narcolepsy.

Narcolepsy is widely believed to have an autoimmune basis, but conventional immunological approaches have failed to detect a serum autoantibody marker. Since cholinergic hyperactivity is a feature of narcolepsy-cataplexy, we transferred IgG from nine patients with narcolepsy and nine healthy controls to mice and assessed the effect on smooth muscle contractile responses to cholinergic stimulation. IgG from all narcolepsy patients significantly enhanced bladder contractile responses to the muscarinic agonist carbachol and to neuronally released acetylcholine compared with control IgG (p<0.0001), whereas contraction of the sympathetically innervated vas deferens was unaltered. Our findings provide direct evidence for the autoimmune hypothesis of narcolepsy.

IgM paraproteinaemia: disease associations and laboratory features.

AIMS: To review the disease associations and laboratory features occurring in IgM paraproteinaemia. METHODS: Systematic review of all new serum IgM paraproteins detected over a 6-year period in an immunodiagnostic laboratory serving a population of 400,000 people. Clinical diagnoses were ascertained from a computerised laboratory database or clinical notes, whilst associated laboratory features were obtained from the same sources. RESULTS: The 125 IgM paraproteins detected constitute 19.7% of all new paraproteins observed over the period of study. IgM paraproteinaemia occurred more commonly in males and its frequency increased with age. Approximately 30% were associated with B cell lymphoproliferative disorders (Waldenstrom's macroglobulinaemia, non-Hodgkin's lymphoma, chronic lymphocytic leukaemia, amyloid, etc.) with the remainder being labelled as monoclonal IgM gammopathies of uncertain significance (four having a peripheral neuropathy). At clinical presentation, patients with lymphoproliferative disorders tended to have higher levels of IgM, beta2-microglobulin, the presence of free urinary light chains and demonstrated molecular size heterogenicity of the paraprotein (presence of decamers, oligomers and monomers in addition to the pentamer) but there was considerable overlap. A good correlation was noted between paraprotein concentration and viscosity in most patients. CONCLUSION: IgM paraproteinaemia was most frequently encountered in the context of a gammopathy of uncertain significance. Features which suggested lymphoproliferative disorders included higher levels of paraprotein (>15 g/l) elevated levels of beta2-microglobulin and the presence of urinary free high chain. However, as much overlap was seen, regular monitoring of paraprotein levels is considered mandatory in the management of these patients.