Passive transfer of autoimmune autonomic neuropathy to mice

Abstract

Autoimmune autonomic neuropathy (AAN) is an acquired, often severe, form of dysautonomia. Many patients with AAN have serum antibodies specific for the neuronal ganglionic nicotinic acetylcholine receptor (AChR). Rabbits immunized with a fusion protein corresponding to the N-terminal extracellular domain of the ganglionic AChR alpha3 subunit produce ganglionic AChR antibodies and develop signs of experimental AAN (EAAN) that recapitulate the cardinal autonomic features of AAN in man. We now demonstrate that EAAN is an antibody-mediated disorder by documenting sympathetic, parasympathetic, and enteric autonomic dysfunction in mice injected with rabbit IgG containing ganglionic AChR antibodies. Recipient mice develop transient gastrointestinal dysmotility, urinary retention, dilated pupils, reduced heart rate variability, and impaired catecholamine response to stress. The autonomic signs are associated with a reversible failure of nicotinic cholinergic synaptic transmission in superior mesenteric ganglia. Mice injected with IgG from two patients with AAN (of three tested) demonstrated a milder phenotype with evidence of urinary retention and gastrointestinal dysmotility. The demonstration that ganglionic AChR-specific IgG causes impaired autonomic synaptic transmission and autonomic failure in mice implicates an antibody-mediated pathogenesis for AAN. The antibody effect is potentially reversible, justifying early use of immunomodulatory therapy directed at lowering IgG levels and abrogating IgG production in patients with AAN.

Figure 1.

Time course of passively transferred EAAN. IgG was injected intraperitoneally on day 0. Data are expressed as mean with SEM (vertical bar). a, Rabbit IgG specific for ganglionic AChR was detectable in mouse plasma 3 weeks after injection. b, Body weight for each mouse is expressed relative to experimental day 0. Mice injected with ganglionic AChR IgG (filled circles) lose weight rapidly for several days and then regain weight. Asterisks indicate days at which their weights differed from control IgG recipient mice (open squares). ^*p < 0.01; ^**p < 0.0001. c, EAAN mice have marked urinary retention. Bladder size is expressed as weight of the bladder and its contents at autopsy. Mean bladder weight of control mice (solid horizontal line) and 95% confidence intervals (broken lines) are shown for comparison.

Figure 2.

Overt signs of EAAN. a, Pupils of mice receiving control IgG were constricted in response to light. Mice with EAAN (3 d after ganglionic AChR IgG injection) had dilated pupils that responded poorly to light. b, At autopsy on day 4 after injection, mice receiving control IgG have a normal appearing bowel and empty bladder (^*). Mice with EAAN show marked urinary retention (^*) and dilated loops of large and small bowel. The proximal small bowel is colored resulting from oral administration of blue dye 30 min before autopsy.

Figure 3.

Autonomic neurophysiology in EAAN. Membrane potential of SMG neurons recorded using intracellular sharp microelectrodes. All SMG neurons from mice injected with rabbit control IgG (Control) showed spontaneous f-EPSPs and APs. When the attached segment of colon is distended (colonic intraluminal pressure is shown in the top trace), the frequency of f-EPSPs and APs increased. SMG neurons from mice injected 2-3 d earlier with rabbit ganglionic AChRIgG (EAAN) had normal resting membrane potential, but many showed no spontaneous or distension-evoked f-EPSPs or APs. Distention of the colon did elicit a slow membrane depolarization. In SMG neurons tested 27 d after injecting ganglionic AChRIgG (Recovery), spontaneous and distension-evoked f-EPSPs were present, and the frequencies of f-EPSPs and APs were higher than in control ganglia.

Figure 4.

Passive transfer of human IgG. a, b, Gastrointestinal transit (a) and bladder size (b) were assessed 4 d after a single injection of human IgG. Mice injected with IgG from patient 2 (n = 5) and mice injected with IgG from patient 3 (n = 4) had reduced transit and increased bladder size. ^*p < 0.05.