EBV and HLA‑DR15: Immunopeptidome Evidence Linking Infection, MBP Peptides and CD4+ T Cells in MS

In an HLA-DR15 context, EBV-transformed B cells displayed specific MBP peptides, and MBP-reactive CD4+ T-cell responses were detected in a subset of HLA-DR15+ multiple sclerosis (MS) samples (including 8 of 16 RRMS peripheral blood samples), the authors report in a study of the HLA-DR15 immunopeptidome.

Investigators present three main lines of evidence: immunopeptidomics from EBV-infected (EBV-transformed) B-cell lines, immunopeptidomics from inflamed MS brain tissue to assess overlap, and functional assays testing peripheral blood and CSF T-cell reactivity to selected MBP epitopes. They also compare findings across compartments relevant to antigen exposure and tolerance, including thymic tissue. The authors interpret these datasets as supporting a mechanistic link between an environmental exposure (EBV) and a genetic risk factor (HLA-DR15) through HLA class II antigen presentation.

To generate these data, the investigators modeled latent EBV infection by infecting primary B cells in vitro to create EBV-transformed B-cell lines, then compared them with primary B cells from HLA-DR15+ donors. Using allele-specific monoclonal antibodies, they immunoprecipitated the two HLA-DR15 allomorphs (DR2a and DR2b), eluted bound peptides, and performed LC-MS/MS to define DR2a- and DR2b-restricted peptide repertoires. In parallel, they report transcriptomic and proteomic profiling to characterize EBV-associated changes in B-cell programs that intersect with antigen processing, along with flow-cytometric assessment of HLA-DR15 surface expression. This setup frames the peptide-level readout as a direct product of DR2a/DR2b antigen presentation under EBV-transformed versus primary B-cell conditions.

Within the EBV-transformed B-cell immunopeptidomes, the authors report four MBP-derived peptides eluted from DR2a and/or DR2b—MBP(78–90), MBP(83–90), MBP(91–106), and MBP(91–114)—and state that these peptides were not detected in primary B-cell immunopeptidomes. They further report that three of these four peptides were also detected among DR2a/DR2b-presented peptides in immunopeptidomes generated from highly inflamed MS brain tissue, while thymic DR2a/DR2b immunopeptidomes from HLA-DR15+ donors did not include MBP(78–90) or MBP(83–90). Presented as convergent observations across sampled compartments, the authors treat detection of these MBP epitopes as a consistent DR15-restricted signal in their datasets.

Functional evidence centered on whether MBP epitope presentation corresponded to detectable memory T-cell responses. Using CD45RA-depleted PBMC preparations from HLA-DR15+ relapsing-remitting MS patients and comparing them with HLA-DR15+ healthy donors, the authors report that patient samples more often showed proliferation to selected MBP epitopes and that responding cultures secreted IFN-γ. In CSF, they report that CD4+ T cells expanded from some HLA-DR15+ patients proliferated in response to these MBP epitopes, with responses varying across individuals and peptides. To probe HLA-DR involvement, they used the pan–HLA-DR blocking antibody L243 and describe partial inhibition of proliferation in several responsive samples. They interpret these assays as supporting HLA-DR–linked, antigen-specific CD4+ memory responses directed at the MBP epitopes identified in their immunopeptidomics work.

On mechanism, the authors emphasize altered antigen processing rather than presenting their results as a demonstration of EBV–MBP molecular mimicry. In EBV-transformed B cells, they report transcriptional and proteomic correlates consistent with enhanced antigen-processing capacity, including upregulated genes spanning proteasome/immunoproteasome components and endosomal proteases, increased autophagy readouts, detection of Golli-MBP transcripts and peptides, and altered intracellular MBP protein levels relative to primary B cells.

The authors note limitations that include immunopeptidomics sensitivity, sample sizes in several experiments, and incomplete ability to exclude low-level presentation in some tissues based on the methods used.

Key Takeaways:

• The authors report that EBV-transformed B cells yielded an HLA-DR15 immunopeptidome containing MBP peptides, whereas these MBP peptides were not detected in primary B-cell immunopeptidomes.
• Investigators observed that three of four EBV_B cell-eluted MBP peptides were also detected in MS brain tissue immunopeptidomes, alongside reported non-detection of MBP(78–90) and MBP(83–90) in thymic DR2a/DR2b immunopeptidomes (a null finding the authors note could reflect immunopeptidomics sensitivity limits).
• The study reports MBP-reactive CD4+ T-cell responses in peripheral blood and in some CSF samples from HLA-DR15+ MS patients, with partial inhibition by the pan–HLA-DR blocking antibody L243 described as supporting evidence.