Bispecificity for Myelin and Neuronal Self-Antigens Is a Common Feature of CD4 T Cells in C57BL/6 Mice

Abstract

The recognition of multiple ligands by a single TCR is an intrinsic feature of T cell biology, with important consequences for physiological and pathological processes. Polyspecific T cells targeting distinct self-antigens have been identified in healthy individuals as well as in the context of autoimmunity. We have previously shown that the 2D2 TCR recognizes the myelin oligodendrocyte glycoprotein epitope (MOG)35–55 as well as an epitope within the axonal protein neurofilament medium (NF-M15–35) in H-2b mice. In this study, we assess whether this cross-reactivity is a common feature of the MOG35–55-specific T cell response. To this end, we analyzed the CD4 T cell response of MOG35–55-immunized C57BL/6 mice for cross-reactivity with NF-M15–35. Using Ag recall responses, we established that an important proportion of MOG35–55-specific CD4 T cells also responded to NF-M15–35 in all mice tested. To study the clonality of this response, we analyzed 22 MOG35–55-specific T cell hybridomas expressing distinct TCR. Seven hybridomas were found to cross-react with NF-M15–35. Using an alanine scan of NF-M18–30 and an in silico predictive model, we dissected the molecular basis of cross-reactivity between MOG35–55 and NF-M15–35. We established that NF-M F24, R26, and V27 proved important TCR contacts. Strikingly, the identified TCR contacts are conserved within MOG38–50. Our data indicate that due to linear sequence homology, part of the MOG35–55-specific T cell repertoire of all C57BL/6 mice also recognizes NF-M15–35, with potential implications for CNS autoimmunity.

NFM Cross-Reactivity to MOG Does Not Expand a Critical Threshold Level of High-Affinity T Cells Necessary for Onset of Demyelinating Disease

“…that NFM expression was not required for T cell mediated EAE (59). This is consistent with the reports that proliferation and cytokine production by MOG specific T cells were markedly diminished by restimulation with NFM compared to cognate MOG (28, 40, 59). We support that CNS T cell infiltrates are functionally responsive to NFM during EAE (14, 28), because pMHC monomers detected T cell cross-recognition of MOG 38-49 and NFM 18-30 by the majority of infiltrates at peak and chronic time points (Fig.…”

“…Our group also found this true for a model antigen system (58). It is not totally unexpected that deletion failed to alter the NFM specific T cell response considering the MHC alterations inherent in NFM 15-35 elicit a weaker association for I-A b than MOG 35-55 (28), which is consistent with the high concentration of NFM required to tolerize EAE compared to MOG (59). In support of this, our studies revealed that cross-reactivity was not altered between wild type and NFM -/- mice because MOG 35-55 induced EAE similarly in both mouse strains (Fig.…”

“…C57BL/6 mice actively challenged with NFM 15-35 using a conventional induction regimen lacked the weight loss and encephalitogenic potential exhibited by MOG 35-55 , Fig. 1B (14, 28). …”

“…4). For MOG 35-55 , evidence suggested that amino acid residues P-1 and P-2 outside of the core nonamer contribute to MHC anchoring and to TCR binding in individual clones (44, 45, 54, 55) with implications for T cell recognition of NFM 15-35 (28). We focused on modulating NFM at P1 (T20Y) to mirror MOG at that position because Petersen et al .…”

“…Currently, polyclonal studies examining T cell specificity to MOG and NFM do not paint a clear model for cross-reactivity and disease because NFM involvement is based on functional responses after MOG 35-55 and not NFM 15-35 priming (28). While this experimental approach stems from earlier reports stating NFM 15-35 does not induce EAE (14), we questioned why this would be the case and chose to comparatively track antigen specific T cells after a MOG 35-55 or NFM 15-35 challenge.…”