MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I PRESENTATION OF EXOGENOUS AND ENDOGENOUS PROTEIN-DERIVED PEPTIDES BY A TRANSFECTED HUMAN MONOCYTE CELL LIFE

Monocyte/macrophages are professional antigen-presenting cells of the cellular immune system. serving to generate peptides for major histoco mpatibility complex (MHC) class II-restricted recognition by CD4(+) T- lymphocyte effector cells. Antigen presentation by these cells involve s the internalization of extracellular proteins and their fragmentatio n within vacuolar compartments. The resulting peptides become associat ed with MHC class II molecules. The final destination of exogenous pep tide antigens, however, is not absolute in monocytes. Processed peptid es, derived from exogenous proteins, can also associate with MHC class I molecules. To study simultaneous presentation of peptides derived f rom exogeneous and endogenous proteins by human Ieucocyte antigen (HLA ) class I molecules, rye isolated the peptides from a human immunodefi ciency virus nef transfected U937 monocytic cell line. The HLA class I -bound peptides were separated by reverse phase-high performance liqui d chromatography. Comparison of the peptide sequence data with protein databases revealed that the peptides derived from extracellular, as w ell as intracellular, proteins, suggesting that monocytes have a more generalized MHC class I antigen-processing pathway than previously doc umented.