Cross-presentation by intercellular peptide transfer through gap junctions.

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Major histocompatibility complex (MHC) class I molecules present endogenous peptides, crucial for T-cell responses.
• Cross-presentation allows professional antigen-presenting cells to present exogenous antigens, but the mechanisms of antigen acquisition are not fully understood.
• Intercellular communication pathways, such as gap junctions, are known to facilitate direct cell-to-cell transfer of molecules.

Purpose of the Study:

• To investigate the direct intercellular transfer of peptides between adjacent cells through gap junctions.
• To determine if this intercellular peptide transfer contributes to antigen acquisition for cross-presentation and T-cell activation.

Main Methods:

• Experimental testing of peptide diffusion between adjacent cells through gap junctions.
• Analysis of peptide size limitations for intercellular transfer.
• Assessment of cytotoxic T-cell recognition of bystander cells and monocytes following intercellular peptide transfer.
• Investigation of the role of cytosolic peptidase activity in restricting peptide transfer.

Main Results:

• Peptides up to approximately 1,800 relative molecular mass can diffuse intercellularly through gap junctions.
• Intercellular peptide transfer leads to cytotoxic T-cell recognition of adjacent bystander cells and activated monocytes.
• High cytosolic peptidase activity restricts gap-junction-mediated peptide transfer to a limited number of coupled cells.

Conclusions:

• Gap-junction-mediated intercellular peptide transfer provides a novel mechanism for antigen acquisition in cross-presentation.
• This process couples the antigen presentation systems of adjacent cells, potentially initiating T-cell responses against innocent bystander cells.
• The described mechanism is implicated in T-cell priming and appears to be impaired in many tumors.