INFLAMMATORY STIMULI INDUCE ACCUMULATION OF MHC CLASS-II COMPLEXES ONDENDRITIC CELLS

Dendritic cells have the remarkable property of presenting any incomin g antigen(1). To do so they must not only capture antigens with high e fficiency and broad specificity, but must also maximize their capacity to load class II molecules of the major histocompatibility complex (M HC) with antigenic peptides in order to present a large array of epito pes from different proteins, each at a sufficient copy number. Here we show that formation of peptide-MHC class II complexes is boosted by i nflammatory stimuli that induce maturation of dendritic cells. In imma ture dendritic cells, class II molecules are rapidly internalized and recycled, turning over with a half-life of about 10 hours. Inflammator y stimuli induce a rapid and transient boost of class II synthesis, wh ile the half-life of dass II molecules increases to over 100 hours. Th ese coordinated changes result in the rapid accumulation of a large nu mber of long-lived peptide-loaded MHC dass II molecules capable of sti mulating T cells even after several days, The capacity of dendritic ce lls to load many antigenic peptides over a short period of initial exp osure to inflammatory stimuli could favour presentation of infectious antigens.