Keystone Epitope Theory: Implications for the Investigation of Multiple Sclerosis

Multiple sclerosis (MS) has long presented a paradox: a strong and reproducible association with Epstein–Barr virus (EBV) exposure despite EBV’s near-universal prevalence. Large prospective cohorts show that EBV seroconversion precedes MS onset and is associated with a marked increase in risk 1, while earlier work links risk to prior infectious mononucleosis and to elevated anti–EBV nuclear antigen 1 (EBNA1) antibody responses 2 3. Yet EBV is clearly not sufficient, implying additional “gates” governed by host genetics, developmental timing, and tissue context. Keystone Epitope Theory (KET) proposes that persistent, human-adapted pathogens such as EBV imprint high-gain immune priorities toward constrained peptide–HLA geometries (“keystone epitopes”), creating plausible vulnerabilities when modified self or foreign antigens accidentally mimic those geometries in the right HLA and niche 4 5 6 7 8 9 10. Applied to MS, KET reframes EBV association as a conditional recall problem: an EBV-trained effector program, often focused on latent antigens such as EBNA1 and deployed in B-cell follicles by cytotoxic T cells (including class II–restricted cytotoxic CD4 T cells), may be redeployed against CNS targets when mimic density and inflammatory context overcome local inhibitory set points. This model can accommodate partial penetrance, epitope spreading, and the strong effects of HLA-DRB1*15:01. The review summarizes key evidence for EBV-focused immunity in MS, highlights newer findings on EBNA1-to-CNS molecular mimicry 11 12 and host–virus genetic convergence 13, and then proposes a practical investigational workflow: lesion-anchored, TCR-forward mapping to identify the keystone epitope and restricting HLA first, followed by a targeted search for homologous CNS mimics, including post-translationally modified (PTM) peptides.