Streptococcus pyogenes and Sydenham Chorea: Molecular Antigenic Mimicry with Barrier-Dependent Neuroimmune Access

Abstract

Abstract Background Other documents in this series have developed vascular access and lesion topology, and cellular second-hit trafficking of adjuvant particles, as convergent but mechanistically distinct routes to compartmental autoimmune or post-infectious disease, within the Access–Mimicry Framework [1]. This document evaluates a fourth, less previously formalized line — molecular antigenic mimicry with neuroimmune barrier access — against an operational four-part framework for causal molecular mimicry derived from Oldstone [2]. Streptococcus pyogenes (Group A Streptococcus, GAS) infection of the pharynx is followed, in a minority of cases, by Sydenham chorea, the major neurological manifestation of acute rheumatic fever. Antibodies raised against the immunodominant N-acetyl-β-D-glucosamine (GlcNAc) epitope of the Group A carbohydrate cross-react with lysoganglioside-GM1 and with tubulin on human neuronal cells [3–4] and activate calcium/calmodulin-dependent protein kinase II (CaMKII) [3]. A separate, independently documented branch of autoantibodies against dopamine D1 and D2 receptors is also associated with active chorea, without an established GlcNAc-based structural homology to those receptors [5]. A murine model of repeated intranasal GAS infection shows Th17 lymphocyte migration into the brain, with microglial activation and BBB disruption concentrated in the olfactory bulb and its direct projection targets, that could provide a candidate neuroimmune-access route [6]. Hypothesis We propose that Sydenham chorea is the clearest human case within this series in which cross-reactive neuronal antibody specificity, barrier-dependent central access, and anatomically selective vulnerability of the basal ganglia converge to produce a single postinfectious compartmental-autoimmune phenotype — a convergence pattern distinct from, and complementary to, this series' vascular-topology and cellular-trafficking lines (Section 2). Sydenham chorea also functions as the positive symmetric counterpart to the Borrelia burgdorferi case note already published in this series [7], where structural cross-reactivity capacity is documented but the four-part framework is explicitly not met, and shares its underlying glycolipid-mimicry logic with the Campylobacter jejuni–Guillain-Barré syndrome case already developed in this series [8], while diverging from it in both compartment (central versus peripheral) and access route (a candidate Th17-associated neuroimmune-access route versus VECT receptor-mediated transcytosis). Conclusions This document evaluates each criterion of that operational framework independently rather than asserting mimicry as a binary verdict, finding criteria 1–2 well supported for Sydenham chorea, criterion 3 supported but assay- and cohort-dependent, and criterion 4 only partially met. It further argues that molecular mimicry establishes antigenic specificity but not sufficiency: because the raft-anchored tubulin target is not straightforwardly accessible to circulating antibody, some additional local neurovascular state — heightened BBB permeability, endothelial transcytosis, or T-cell-driven inflammation, of which a vaccine-adjuvant second hit is treated as one candidate contributor — is needed to explain why disease develops in some antibody-positive children and not others; this document treats the exact source of that local state as an open, falsifiable question (Section 5) rather than assuming any single answer. Seven falsifiable predictions are proposed. Streptococcus pyogenes and Sydenham chorea are retained as this series' first positive case of molecular antigenic mimicry with barrier-dependent neuroimmune access, reinforcing this series' central thesis that autoimmunity is a convergent phenotype reachable by structurally distinct causal architectures, not a single mechanistic kind.