Differential expression of the granzymes A, K and M and perforin in human peripheral blood lymphocytes

Granzymes (Gzm) are a group of serine proteases which are stored in the granules of cytotoxic lymphocytes. In humans, five granzymes have been characterized to date at the molecular level. While GzmA and GzmB have been extensively studied, little is known about GzmH, GzmK and GzmM. In this study, we describe the generation of mAbs against human GzmK and GzmM by genetic immunization. The obtained anti-GzmK and anti-GzmM mAbs are not cross-reactive with GzmA, GzmB, GzmM and GzmA, GzmB, GzmK, respectively, and show a granular staining pattern in human lymphocytes. Flow cytometric analysis of peripheral blood lymphocytes revealed that GzmA, GzmM and perforin show a similar distribution. They are expressed in almost all CD16(+)CD56(+) NK cells, CD3(+)CD56(+) NKT cells and gamma delta T cells as well as in 20-30% of all CD3(+)CD8(+) T-C cells. Surprisingly, GzmK was not detected in the highly cytotoxic CD16(+)CD56(+) NK cells but was preferentially expressed in lymphocytes of the T cell lineage, staining 20% of CD3(+)CD8(+) T-C cells, 50% of CD3(+)CD56(+) NKT cells and 40% of gamma delta T cells, as well as 60% of the small sub-population of CD56(bright+) NK cells. Our data suggest that human granzymes are differentially expressed in distinct sub-populations of peripheral blood lymphocytes.