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Presentation of mouse tum− P91A antigen from chimeric proteins with different subcellular localizations by class I molecules of the major histocompatibility complex

Like many antigens presented by class I molecules the mouse Ld‐binding turn−antigen P91A derives from a cytosolic protein. To decide how stringent this localization is for presentation to cytotoxic lymphocytes (CTL) the P91A template has been inserted in the cDNA of rat esterase ES‐10, a protein located in the endoplasmic reticulum (ER), and in the cDNA of mouse interleukin‐9, a secretory product of lymphocytes. The esterase construct was also engineered to replace the C‐terminal leucine by arginine, which causes secretion of the protein, or to delete the N‐terminal presequence, which prevents transfer of the nascent chain to the ER. After cell‐free transcription‐translation, or transfection in COS cells, the products of the chimeric cDNA had the expected size and localization; however, the truncated form of esterase remained undetected in COS cells. The various chimeric templates were transfected in Pl.HTR cells (H‐2d); upon challenge with Ld‐restricted anti‐P91A CTL the cells were lyzed almost as efficiently as cells transfected with the full‐length P91A cDNA. We conclude that peptide fragments that bind to class I molecules of the major histocompatibility complex can be generated in the ER.