Short peptides sensitize target cells to CTL specific for the MHC class Ib molecule, H2-M3

Area of Science:

• Immunology
• Molecular Biology
• Mitochondrial Genetics

Background:

• MHC class Ib molecule H2-M3 presents N-formylated peptides derived from mitochondrial proteins to cytotoxic T lymphocytes (CTLs).
• Understanding the optimal peptide length for H2-M3 presentation is crucial for dissecting T cell recognition of mitochondrial antigens.

Purpose of the Study:

• To determine the optimal peptide length for H2-M3-restricted CTL recognition of mitochondrial peptides.
• To investigate the natural processing and presentation of endogenous mitochondrial peptides in target cells.

Main Methods:

• Generation and characterization of CTL lines and clones specific for N-formylated peptides from mitochondrial proteins (COI and ND1).
• Sensitization of antigen-deficient target cells with synthetic peptides of varying lengths.
• Assessment of CTL lysis of sensitized target cells and lymphoblasts expressing endogenous mitochondrial antigens.

Main Results:

• Most CTL lines and clones efficiently lysed target cells sensitized with a COI hexamer or an ND1 heptamer.
• A minority of anti-ND1 CTL clones showed a preference for octamer or nonamer peptides; no CTL required longer peptides.
• CTL recognition of short peptides correlates with the known shortened peptide-binding groove of H2-M3.
• All tested CTLs lysed lymphoblasts expressing the relevant mitochondrial antigen, indicating natural processing and presentation of endogenous formylated peptides (6-9 amino acids).

Conclusions:

• The optimal length for H2-M3-presented mitochondrial peptides recognized by CTLs is generally short (6-9 amino acids).
• This finding aligns with the structural constraints of the H2-M3 binding groove.
• Naturally processed mitochondrial peptides presented by H2-M3 on target cells are endogenous, N-formylated, and range from six to nine amino acids in length.