INTERLEUKIN-10 DOWN-REGULATES MHC CLASS-II ALPHA-BETA PEPTIDE COMPLEXES AT THE PLASMA-MEMBRANE OF MONOCYTES BY AFFECTING ARRIVAL AND RECYCLING

Interleukin-10 (IL-10) inhibits antigen-specific T cell responses when human monocytes are used as antigen-presenting cells. This is correla ted with a downregulation of MHC class II molecules on the surface of the monocyte. Here we show that IL-10 does not affect MHC class II tra nscription, polypeptide synthesis, subunit assembly, or antigenic pept ide loading. Instead, newly synthesized mature MHC class II molecules are localized to the MHC class II loading compartment but are prevente d from reaching the plasma membrane. In addition, treatment of monocyt es with IL-10 leads to an accumulation of internalized MHC class II co mplexes in intracellular vesicles. These results indicate that IL-10 a ffects antigen presentation by regulating MHC exocytosis and recycling .