GENERATION OF ANTIGENIC PEPTIDES BY LYMPHOCYTE GRANULE SERINE PROTEASES (GRANZYMES)

We have examined the ability of several serine proteases (granzymes) i solated from the granules of the rat natural killer cell line, RNK, to generate antigenic peptides of ovalbumin (Oval that are capable of be ing recognized by Ova-specific CD8(+) T cells. The mouse MHC class I-r estricted cytotoxic T-cell clone, GX-1, which recognizes a trypsinized fragment of Ova in the context of H-2(b), was able to lyse EL4 (H-2(b )) target cells in the presence of Ova and the granzymes but not in th e presence of Ova or granzymes alone. Similar results were obtained us ing the murine Ova-specific CD8(+) T cell hybridomas, RF33.70 and CD80 VA. In all cases, the T cells' responses were MHC class I-restricted a s Ova:granzyme mixtures failed to mediate the lysis of the MHC-dispara te target cell, P815 (H-2(d)), The purified rat granzyme preparations contained three distinct enzymatic specificities: asp-ase, met;ase, an d tryptase. Aprotinin, a protease inhibitor that only inhibits tryptas e activity in vitro, completely abolished the CD8(+) T-cell responses to Ova. These results, along with peptide loading studies using the RM A-S cell line, suggest that the granzyme treatment of Ova can generate the proper antigenic fragments which facilitate class I-restricted CT L responses both in vivo and in vitro. We believe that enzymes produce d and released by NK or cytotoxic T cells within a tissue microenviron ment may enhance the cleavage of-target cell antigens as well as solub le antigens resulting in the improved uptake and processing of soluble antigens. (C) 1996 Academic Press, Inc.