MHC class II and CD40 play opposing roles in dendritic cell survival

Area of Science:

• Immunology
• Cell Biology

Background:

• Mature dendritic cells (DCs) exhibit differential susceptibility to death receptor-mediated apoptosis.
• Dendritic cell (DC) maturity influences resistance to CD95 (also known as APO-1) ligation-induced cell death.

Purpose of the Study:

• To investigate the susceptibility of mature DCs to apoptosis induced by other death ligands.
• To elucidate the mechanisms and regulatory pathways involved in DC apoptosis and survival.

Main Methods:

• Induction of apoptosis in mature DCs using anti-I-A/I-E monoclonal antibodies (mAb) targeting MHC class II.
• Assessment of apoptosis via annexin/propidium iodide staining, morphological changes, and mitochondrial membrane potential.
• Investigation of CD40-mediated protection against MHC class II-induced apoptosis, including the role of signaling pathways like p38 MAPK.

Main Results:

• Mature DCs are highly susceptible to apoptosis induced by cross-linking of MHC class II, contrasting with their resistance to CD95-mediated death.
• MHC class II-mediated killing requires DC cytoskeletal motion, divalent cations, and phosphatase activity, but not caspase activation or de novo synthesis.
• CD40 mAb cross-linking, but not lipopolysaccharide or TNF-alpha, conferred complete resistance to MHC class II-induced apoptosis, partly mediated by the p38 MAPK pathway.

Conclusions:

• DC maturity correlates with increased resistance to CD95 killing and increased susceptibility to MHC class II-mediated killing.
• CD40 activation provides a crucial survival signal against MHC class II-induced apoptosis in DCs.
• These findings underscore the role of T cell interactions, via CD40, in regulating dendritic cell survival and function.