Characterization of a peptide-loading compartment by monoclonal antibodies

Whether or not peptide-loading compartments are classical or specialized co mpartments of the endocytic pathway of antigen presenting cells is still a matter of debate. One way to solve this discrepancy would be to characteriz e specific markers for the peptide-loading compartment. We chose to generat e monoclonal antibodies against the peptide-loading compartment that we pre viously characterized as lysozyme loading compartment (LLC) [Escola, J.M., Grivel, J.C., Chavrier, P., Gorvel, J.P., 1995. Different endocytic compart ments are involved in the tight association of class II molecules with proc essed hen egg lysozyme and ribonuclease A in B cells. J. Cell Sci. 108, 233 7; Escola, J.M., Deleuil, F., Stang, E., Boretto, J., Chavrier, P., Gorvel, J.P., 1996. Characterization of a lysozyme-major histocompatibility comple x class II molecule-loading compartment as a specialized recycling endosome in murine B lymphocytes. J. Biol Chem. 271, 27360], A preliminary screenin g by dot blot enabled us to identify several monoclonal antibodies recogniz ing the LLC and not early and late endosomes, One of these antibodies, the 20C4, was then characterized. It is directed against mature class II molecu les of all murine haplotypes. By electron microscopy, 20C4 labeling was res tricted to both the plasma membrane and the LLC, These reagents may be usef ul in the further characterization of the specialized function of these int racellular organelles. (C) 1999 Elsevier Science B.V. All rights reserved.