This analogue of the encephalitogenic PLP 139-151 epitope carries glutamine in place of the native tryptophan at position 144, the sixth residue of the supplied sequence. The native epitope drives relapsing experimental autoimmune encephalomyelitis in SJL/J mice and is among the most heavily used autoantigens in multiple sclerosis modelling. The substitution here is chemically distinct from the alanine and leucine analogues offered alongside it. Glutamine is polar and capable of hydrogen bonding, where alanine simply deletes the contact and leucine preserves bulk and hydrophobicity without the aromatic ring. Substituting at the dominant T-cell receptor contact with side chains of differing chemistry is how the series distinguishes receptors that require aromaticity from those that require only volume, or that can accommodate a polar partner. Analogues of this epitope have produced outcomes across the full range, including heteroclitic responses in which a substituted peptide elicits a stronger response than the native antigen together with a shifted cytokine profile. That possibility is worth anticipating: an altered peptide ligand cannot be assumed to be weaker than the parent, and dose-response comparison against native PLP 139-151 rather than single-concentration testing is the reliable way to characterise it in a given responder population. | 