RECONSTITUTION OF AN OPERATIONAL MHC CLASS-II COMPARTMENT IN NONANTIGEN-PRESENTING CELLS

Professional antigen-presenting cells (APCs) have a distinct compartme nt in which class II molecules are proposed to acquire antigenic pepti des. Genetic evidence suggests that human leukocyte antigen (HLA)-DM, an unusual class II molecule, participates in this process. Peptide ac quisition was reconstituted in nonprofessional APCs by transfection of class II, invariant chain (Ii), and H-2M, the murine equivalent of DM . The H-2M heterodimer appeared in an endosomal compartment, not at th e cell surface, and the localization was independent of Ii. The data p resented show that H-2M, class II, and Ii are the minimally required c omponents for efficient formation of stable class II-peptide complexes , and thus for a functional class II compartment.