Granzyme K (GrK) is a member of a highly conserved group of potent
serine proteases specifically found in the secretory granules of cytotoxic T lymphocytes and natural killer cells. Based on the report indicating that
inter-alpha inhibitor proteins are the physiological inhibitors of GrK and on previous findings that showed a significant decrease in plasma
inter-alpha inhibitor proteins in patients with
sepsis, it was our aim to determine whether increased levels of uninhibited GrK would contribute to the development of
sepsis. To test this hypothesis, a competitive
enzyme-linked
immunosorbent assay system was developed; and the levels of GrK were measured in plasma samples obtained from healthy controls and 2 sets of patients with
sepsis: patients admitted to the emergency department with a putative diagnosis of
sepsis and patients with
severe sepsis enrolled in a clinical trial. In addition, the molecular form(s) of GrK present in these samples was analyzed by Western blot. The levels of GrK were significantly increased in emergency department patients compared with healthy controls and significantly decreased in patients with
severe sepsis enrolled in a clinical trial compared with healthy controls. GrK was detected as high-molecular-weight
protein complexes in healthy controls but as complexes of lower molecular weight in the septic patients. The decrease in complex size correlated with the appearance of a band at 26 kDa similar to the size of free GrK. Our results indicate that plasma levels of GrK could serve as a useful diagnostic marker to stage
sepsis, permitting better classification of septic patients and enabling targeting of specific treatments, and may play a functional role in the development of
sepsis.