Small fibre integrity and axonal pathology in the rat model of experimental autoimmune neuritis

Experimental autoimmune neuritis is a common animal model for acute human immune-mediated polyneuropathies. Although already established in 1955, a number of pathophysiological mechanisms remain unknown. In this study, we extensively characterize experimental autoimmune neuritis progression in Lewis rats, including new insights into the integrity of small nerve fibres, neuropathic pain and macrophage activation. Acute experimental autoimmune neuritis was induced with $P2_{53–78}$ peptide and consequently investigated using the gait analysis system CatWalk XT, electrophysiological and histopathological analyses, quantitative polymerase chain reaction (PCR), dorsal root ganglia outgrowth studies, as well as the von Frey hair and Hargreaves tests. For the longitudinal setup, rats were sacrificed at Day (d) 10 (onset), d15 (peak), d26 (recovery) and d29 (late recovery). We confirmed the classical T-cell and macrophage-driven inflammation and the primarily demyelinating nature of the experimental autoimmune neuritis. The dual role of macrophages in experimental autoimmune neuritis is implicated by the high number of remaining macrophages throughout disease progression. Furthermore, different subpopulations of macrophages based on $\textit {Cx3-motif chemokine receptor 1 (Cx3cr1), platelet factor 4 (Pf4)}$ and $\textit {macrophage galactose-type lectin-1 (Mgl1)}$ expressions were identified. In addition, modulation of the sensory system in experimental autoimmune neuritis was detected. An outgrowth of small fibres in the plantar skin at the onset and peak of the experimental autoimmune neuritis was evident parallel to the development of acute hyperalgesia mediated through transient receptor potential vanilloid 1 modulation. Our data depict experimental autoimmune neuritis as a primary demyelinating disease with implicated axonal damage, a small unmyelinated fibre impairment throughout the disease progression course, and underline the pivotal role of macrophages in the effector and during the recovery stage

Association of the neonatal Fc receptor promoter variable number of tandem repeat polymorphism with immunoglobulin response in patients with chronic inflammatory demyelinating polyneuropathy

$\textbf {Background and purpose:}$ Chronic inflammatory demyelinating polyneuropathy (CIDP) is an autoimmune disease with humoral and cellular autoimmunity causing demyelination of peripheral nerves, commonly treated with intravenous immunoglobulins (IVIg). The neonatal Fc receptor (FcRn), encoded by the $\it FCGRT$ gene, prevents the degradation of immunoglobulin G (IgG) by recycling circulating IgG. A variable number of tandem repeat (VNTR) polymorphism in the promoter region of the $\it FCGRT$ gene is associated with different expression levels of mRNA and protein. Thus, patients with genotypes associated with relatively low FcRn expression may show a poorer treatment response to IVIg due to increased IVIg degradation. $\bf Methods:$ VNTR genotypes were analyzed in 144 patients with CIDP. Patients' clinical data, including neurological scores and treatment data, were collected as part of the Immune-Mediated Neuropathies Biobank registry. $\bf Results:$ Most patients ($\it n$ = 124, 86%) were VNTR 3/3 homozygotes, and 20 patients (14%) were VNTR 2/3 heterozygotes. Both VNTR 3/3 and VNTR 2/3 genotype groups showed no difference in clinical disability and immunoglobulin dosage. However, patients with a VNTR 2 allele were more likely to receive subcutaneous immunoglobulins (SCIg) than patients homozygous for the VNTR 3 allele (25% vs. 9.7%, $\it p$ = 0.02) and were more likely to receive second-line therapy (75% vs. 54%, $\it p$ = 0.05). $\bf Conclusions:$ The VNTR 2/3 genotype is associated with the administration of SCIg, possibly reflecting a greater benefit from SCIg due to more constant immunoglobulin levels without lower IVIg levels between the treatment circles. Also, the greater need for second-line treatment in VNTR 2/3 patients could be an indirect sign of a lower response to immunoglobulins