Protein kinase C delta stimulates antigen presentation by Class II MHC in murine dendritic cells

Maturation of dendritic cells (DCs) regulates protein sorting in endosomal compartments to promote the surface expression of molecules involved in T cell activation. MHC Class II complexes are mobilized to the surface via intracellular effector molecules that remain largely unknown. We here show that protein kinase C (PKC) stimulates Class II antigen surface expression, using knock-in mice that express a Class II-green fluorescent protein fusion protein as a read out. Selective inhibition of PKC delta counteracts the ability of DCs to stimulate Class II MHC-restricted antigen-specific T cells. Activation of PKC does not affect antigen uptake, peptide loading and surface display of Class 1 MHC and transferrin receptor in DCs. We show that activation-induced Class 11 MHC surface expression is dependent on activation of PKC delta and conclude that this event is pivotal for optimal CD4 T cell activation.