Processing of MOG is Affected by Post-Translational Modification in Virus Infected Non-Human Primate B Cells

The non-human primate experimental autoimmune encephalomyelitis (EAE) model provides a unique opportunity to study several pathogenic mechanisms of multiple sclerosis, due to its close resemblance to humans. We have shown that in the common marmoset, a New World monkey, sensitization against myelin oligodendrocyte glycoprotein peptide 34–56 (MOG34-56) in incomplete Freund's adjuvant (IFA) involved activation of Natural Killer-cytotoxic T lymphocytes (NK-CTL), which leads to severe demyelination of the grey and white matter and neurological symptoms. However, the same immunization protocol in rhesus macaques was not effective in inducing clinically evident EAE. Nevertheless, gamma-herpesvirus transformed B cells (such as with EBV) from both species were equally able to act as antigen presenting cells for the activation of MOG34-56 specific NK-CTL. The aim of this study was to assess whether there is a difference in uptake and processing of MOG34-56 by primary versus gamma-herpes-infected B cells of both species. Proteolytic degradation of both the marmoset and rhesus monkey MOG34-56 peptide, which is occupied by a proline in the rhesus and a serine in the marmoset sequence at position 42, was investigated using primary and transformed B cell lysates with mass spectrometry and SDS-PAGE gel analysis. In addition, also peptides were tested where the arginine residue at position 41 and/or 46 was citrullinated. This is a common post-translational modification of peptides in virus infected B cells. We found that the rhesus monkey peptide, even with the citrulline modifications, was totally destroyed during processing by the primary as well as by the transformed B cells, a phenomenon know as destructive processing. The marmoset sequence was protected from destructive processing with a citrulline substitution on position 46. The data indicate an unexpected role of B cells in the prevention of autoimmunity in the non-human primate EAE model by destructive processing of the highly pathogenic epitope (MOG40-48) within the MOG34-56 sequence. Moreover, gamma-herpesvirus infection abrogated this protective mechanism by rescuing the MOG40-48 epitope from destruction.