CTL EPITOPE GENERATION IS TIGHTLY LINKED TO CELLULAR PROTEOLYSIS OF ALISTERIA-MONOCYTOGENES ANTIGEN

Listeria monocytogenes is a pathogenic intracellular bacterium that se cretes proteins into the cytosol of host cells, A major secreted prote in, p60, is processed by the host cell into the nonamer peptides p60 2 17-225 and p60 449-457, which are presented to CTL by H-2K(d) MHC clas s I molecules, Herein, we use two membrane permeable peptide aldehyde protease inhibitors, LLnL and Z-LLF, to inhibit cytosolic proteolysis in L. monocytogenes-infected cells. These inhibitors, which have been shown to inhibit proteasomes, completely abrogate cytosolic p60 degrad ation, The effect of LLnL and Z-LLF on p60 epitope generation was dete rmined by acid-eluting, HPLC-purifying, and quantifying p60 217-225 an d p60 449-457 from infected cells, We show a direct linkage between p6 0 degradation and epitope generation, However, the two inhibitors have quantitatively different effects on the generation of the two epitope s, Our findings implicate proteasomes in the earliest stages of Ag deg radation and suggest that different CTL epitopes can be generated by d istinct proteolytic processes.