Granzyme K-deficient mice show no evidence of impaired antiviral immunity.

The biological role of granzyme K, a serine protease of cytotoxic T lymphocytes (CTL), is controversial. It has been reported to induce perforin-mediated cell death in vitro, but is also reported to be non-cytotoxic and to operate in inflammatory processes. To elucidate the biological role of this protease, we have deleted the granzyme K gene in mice (mutant allele: Gzmktm1.1Pib; MGI:5636646). Gzmk -/- mice are healthy, anatomically normal, fecund and show normal hematopoietic development. Gzmk -/- mice readily recover from lymphocytic choriomeningitis virus and mouse pox Ectromelia virus infection. Ex vivo, virus-specific granzyme K-deficient CTL are indistinguishable from those of wild-type mice in apoptosis induction of target cells. These data suggest that granzyme K does not play an essential role in viral immunity or cytotoxicity. Our granzyme K knockout line completes the collection of mouse models for the human granzymes, and will further our understanding of their biological roles and relationships.

Are all granzymes cytotoxic in vivo?

Abstract Granzymes are serine proteases mainly found in cytotoxic lymphocytes. The most-studied member of this group is granzyme B, which is a potent cytotoxin that has set the paradigm that all granzymes are cyototoxic. In the last 5 years, this paradigm has become controversial. On one hand, there is a plethora of sometimes contradictory publications showing mainly caspase-independent cytotoxic effects of granzyme A and the so-called orphan granzymes in vitro. On the other hand, there are increasing numbers of reports of granzymes failing to induce cell death in vitro unless very high (potentially supra-physiological) concentrations are used. Furthermore, experiments with granzyme A or granzyme M knock-out mice reveal little or no deficit in their cytotoxic lymphocytes' killing ability ex vivo, but indicate impairment in the inflammatory response. These findings of non-cytotoxic effects of granzymes challenge dogma, and thus require alternative or additional explanations to be developed of the role of granzymes in defeating pathogens. Here we review evidence for granzyme cytotoxicity, give an overview of their non-cytotoxic functions, and suggest technical improvements for future investigations.

Interleukin-1R signaling is essential for induction of proapoptotic CD8 T cells, viral clearance, and pathology during lymphocytic choriomeningitis virus infection in mice.

The T cell granule exocytosis pathway is essential to control hepatotropic lymphocytic choriomeningitis virus strain WE (LCMV-WE) but also contributes to the observed pathology in mice. Although effective antiviral T cell immunity and development of viral hepatitis are strictly dependent on perforin and granzymes, the molecular basis underlying induction of functionally competent virus-immune T cells, including participation of the innate immune system, is far from being resolved. We demonstrate here that LCMV-immune T cells of interleukin-1 receptor (IL-1R)-deficient mice readily express transcripts for perforin and granzymes but only translate perforin, resulting in the lack of proapoptotic potential in vitro. LCMV is not cleared in IL-1R-deficient mice, and yet the infected mice develop neither splenomegaly nor hepatitis. These results demonstrate that IL-1R signaling is central to the induction of proapoptotic CD8 T cell immunity, including viral clearance and associated tissue injuries in LCMV infection.

Blessing or curse? Proteomics in granzyme research.

Granzymes (gzms) are a group of serine proteases that play an important role in innate and adaptive immunity, blood coagulation, apoptosis, and inflammation, but are also connected to atherosclerosis, diabetes, cardiovascular and inflammatory lung diseases, cancer, and sepsis. Humans have five gzms (gzms A, B, H, K, and M), which differ in their substrate specificity. It is widely accepted that they are delivered from cytotoxic lymphocytes via perforin into the cytoplasm of target cells where they initiate cell death, modulate cytokine signaling, or inactivate pathogen proteins. However, more recent evidence indicates gzms also act extracellularly in noncytotoxic processes. Proteomic approaches are directed at mapping gzm cleavage specificity, identifying substrates, and unraveling the (patho-) physiological role of these proteases. These studies have refined our understanding of gzm species specificity, and collectively uncovered an enormous number of new substrates. However, with the exception of a very few human gzmB substrates supported by independent data (Bid, DNA-PK, PARP, ICAD, and procaspase 7), it is presently unclear which are physiologically relevant. This review aims to summarize and analyze the different proteomic approaches used and discuss both their convincing and controversial outcomes.