Altered peptide ligands of myelin basic protein (MBP87–99) conjugated to reduced mannan modulate immune responses in mice

摘要

Mutations of peptides to generate altered peptide ligands, capable of switching immune responses from T helper 1 (Th1) to T helper 2 (Th2), are promising candidates for the immunotherapy of autoimmune diseases such as multiple sclerosis (MS). We synthesized two mutant peptides from myelin basic protein 87–99 (MBP87–99), an immunodominant peptide epitope identified in MS. Mutations of residues K91 and P96, known to be critical T-cell receptor (TCR) contact sites, resulted in the mutant peptides [R91, A96]MBP87–99 and [A91, A96]MBP87–99. Immunization of mice with these altered peptide ligands emulsified in complete Freund’s adjuvant induced both interferon-γ (IFN-γ) and interleukin-4 (IL-4) responses compared with only IFN-γ responses induced to the native MBP87–99 peptide. It was of interest that [R91, A96]MBP87–99 conjugated to reduced mannan induced 70% less IFN-γ compared with the native MBP87–99 peptide. However, [A91, A96]MBP87–99 conjugated to reduced mannan did not induce IFN-γ-secreting T cells, but elicited very high levels of interleukin-4 (IL-4). Furthermore, antibodies generated to [A91, A96]MBP87–99 peptide conjugated to reduced mannan did not cross-react with the native MBP87–99 peptide. By molecular modelling of the mutant peptides in complex with major histocompatibility complex (MHC) class II, I-As, novel interactions were noted. It is clear that the double-mutant peptide analogue [A91, A96]MBP87–99 conjugated to reduced mannan is able to divert immune responses from Th1 to Th2 and is a promising mutant peptide analogue for use in studies investigating potential treatments for MS.