Predominant HLA-Class I1 Bound Self-peptides of a Hematopoietic Progenitor Cell Line Are Derived From Intracellular Proteins

Human myeloid progenitor cells temporarily express HLA class II molecules during the differentiation pathway to granulocytes and macrophages. The significance of major histocompatibility complex ( “ 3 class II molecules at this stage of development is unknown. As a first step of inquiry into their function, we have characterized the profile of major self-peptides bound to the HLA-DR molecules expressed by KG-l cells, a line that shares many of the phenotypic characteristics of colony-forming unit-granulocyte-macrophage progenitors. Searches of protein data bases showed that all matching peptides bound to the HLA-DR molecules of KG1 cells corresponded to intracellular, rather than exogenous or transmembrane, precursor proteins. Because the absence of a conventional self-peptide repertoire could be related to altered trafficking of class II molecules, the biosynthesis of HLA-DR and the invariant chain proteins was determined.