We have tested the hypothesis that phenotypic changes of development are accompanied by expression of differentiation-stage specific peptides bound to major histocompatibility complex (MHC) class I molecules. The U937 cell line, when cultured in the presence of phorbol myristate acetate (PMA), undergoes differentiation from monoblasts to macrophage-like cells. The high-performance liquid chromatography profile of peptides eluted from purified human histocompatibility leukocyte antigen class I molecules expressed by U937 treated with PMA differs from that obtained from control, untreated U937 cells. Chemical sequencing of eluted peptides identified a peptide derived from cytomegalovirus in both treated and untreated cells. PMA-treated, but not untreated cells, displayed an additional peptide derived from interleukin 1 beta. Hence, differentiation-induction of U937 is accompanied by the presentation of at least one differentiation-stage specific peptide. Our results indicate that, similar to viral infection, cellular development and transformation is accompanied by the de novo synthesis of proteins which are processed and presented on MHC class I molecules.

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