The lectin Siglec-G inhibits dendritic cell cross-presentation by impairing MHC class I-peptide complex formation

Area of Science:

• Immunology
• Cell Biology

Background:

• CD8α(+) dendritic cells (DCs) are key for initiating cytotoxic T lymphocyte (CTL) responses via cross-presentation of extracellular antigens on MHC class I.
• Mechanisms regulating DC cross-presentation are not fully understood.

Purpose of the Study:

• To investigate the role of Siglec-G in regulating CD8α(+) DC cross-presentation.
• To elucidate the molecular mechanisms by which Siglec-G affects cross-presentation.

Main Methods:

• Comparative analysis of Siglec-G expression in CD8α(+) DCs.
• Assessment of CTL responses in wild-type and Siglec-G deficient (Siglecg(-/-)) mice.
• Quantification of MHC class I-peptide complexes on DCs.
• Investigation of molecular interactions involving Siglec-G, SHP-1, p47(phox), and NOX2.

Main Results:

• Siglec-G expression is lower in CD8α(+) DCs.
• Siglec-G deficiency leads to increased antigen-specific CTL responses, enhancing control of bacterial infection and tumor growth.
• Mice lacking Siglec-G exhibit higher abundance of MHC class I-peptide complexes on CD8α(+) DCs.
• Siglec-G recruits SHP-1 phosphatase, which dephosphorylates p47(phox), inhibiting NOX2 activation and leading to excessive antigen hydrolysis and reduced MHC class I-peptide complex formation.

Conclusions:

• Siglec-G acts as an inhibitor of DC cross-presentation by impairing MHC class I-peptide complex formation.
• These findings provide novel insights into the regulation of adaptive immunity through DC cross-presentation.