# Blood–Nerve Barrier Breakdown Induced by Immunoglobulin G in Typical and Multifocal Chronic Inflammatory Demyelinating Polyneuropathy and Multifocal Motor Neuropathy

## TL;DR

This study explores how immunoglobulin G from patients with certain nerve disorders breaks down the blood-nerve barrier, potentially causing inflammation in the nervous system.

## Contribution

The study identifies specific molecular pathways and proteins involved in blood-nerve barrier disruption in different types of neuropathies.

## Key findings

- IgG from typical CIDP patients upregulates TNF-α, CCL20, and ICAM-1 in endothelial cells.
- Multifocal CIDP and MMN IgG increase GM-CSF and VCAM-1, reducing barrier integrity.
- Neutralizing GM-CSF reverses increased permeability in cocultured endothelial and pericyte cells.

## Abstract

Impairment of the blood–nerve barrier (BNB) is associated with the pathogenesis of chronic inflammatory demyelinating polyneuropathy (CIDP) and multifocal motor neuropathy (MMN). This research analyzes the molecular mechanisms of immunoglobulin (Ig) G in patients with typical CIDP, CIDP variants (multifocal CIDP), and multifocal motor neuropathy in BNB-endothelial cells. IgG was purified from the sera of patients with typical CIDP (n = 15), multifocal CIDP (n = 14), multifocal motor neuropathy (MMN; n = 12), and healthy controls (HCs; n = 14). Molecular changes in the RNA-seq/high-content imaging system and permeability were evaluated after the incubation of human peripheral nerve microvascular endothelial cells (PnMECs) with IgG. RNA-seq and a pathway analysis using PnMECs showed that TNF-α, CCL20 (MIP-3α), and ICAM-1 were the centers of the upregulated gene pathways in patients with typical CIDP. TNF-α, VCAM-1, NF-κB, and CSF2 (GM-CSF) are important molecules in patients with multifocal CIDP. The high-content imaging system demonstrated that MIP-3, GM-CSF, and VCAM-1 increased after exposure to typical CIDP-IgG, claudin-5 decreased after exposure to IgG from patients with multifocal CIDP, and TNF-α and VCAM-1 increased after exposure to IgG from patients with MMN. The 10 kDa dextran permeability using coculture with PnMECs and pericytes increased after exposure to IgG from patients with typical CIDP and multifocal CIDP. This effect was reversed after incubation with GM-CSF neutralizing antibodies. Upregulation of MIP-3, GM-CSF, and VCAM-1 may contribute to the infiltration of leukocytes/lymphocytes/monocytes across the BNB into the PNS in typical CIDP. IgG from typical CIDP and multifocal CIDP may decrease barrier properties through autocrine GM-CSF from PnMECs. VCAM-1 upregulation through autocrine TNF secretion in PnMECs may induce lymphocyte entry across the BNB in MMN.