Complement-Regulated Nodal Vulnerability in Guillain-Barré Syndrome and  CIDP.

The immunobiology of Guillain-Barré syndrome (GBS) has long been organized around a dichotomy: acute motor axonal neuropathy (AMAN) is an antibody-mediated nodal disorder, whereas acute inflammatory demyelinating polyneuropathy (AIDP) has been interpreted mainly through T-cell-mediated models of compact-myelin injury. Four successive findings challenge this separation. Intraneural injection of GBS sera produced demyelination without transfer of immune cells; pathological studies in AIDP localized complement activation to the Schwann-cell surface before macrophage-associated myelin stripping. Serum IgG from a substantial subset of patients with AIDP bound nodal or paranodal surface domains; and identification of gelsolin-3 defined an AIDP subset in which patient IgG, together with active complement, produced nodal disruption before internodal demyelination. Peripheral-myelin-reactive T cells further indicate that T-cell-mediated and antibody-mediated immunity may coexist. Within this evidence hierarchy, AMAN and a subset of AIDP have distinct initiating targets but converge on nodal dysfunction. CD55 and CD59 are membrane-bound complement regulators: CD55 limits complement amplification, whereas CD59 prevents assembly of the membrane attack complex. Both are detectable in compact myelin but not at human nodes of Ranvier, revealing a localized discontinuity in complement control. This local absence of complement regulators may influence whether antibody binding progresses to conduction failure, axonal degeneration, or internodal demyelination, but should be regarded as a permissive substrate for injury rather than as evidence of lesion localization. Observations in chronic inflammatory demyelinating polyneuropathy (CIDP) suggest that antibody-mediated functional injury may precede structural demyelination. This Review proposes complement-regulated nodal vulnerability to integrate evidence across AMAN and subsets of AIDP and CIDP while preserving differences in targets, tempo, and mechanistic strength.