Detection of soluble human granzyme K in vitro and in vivo

Abstract

Granzymes are serine proteases released from the granules of cytotoxic lymphocytes during the induction of apoptosis. To evaluate the physiologic role of human granzyme K (GzmK), we developed a sensitive ELISA which was shown to specifically detect human GzmK in its active as well as its inactive conformation. Analysis of the lysate of lymphokine‐activated killer (LAK) cells by gel filtration revealed that GzmK seems to be complexed to proteoglycans within these cells. While the expression of GzmA and B by cytotoxic lymphocytes was strongly up‐regulated in response to several activating stimuli, GzmK expression did not increase significantly above constitutive levels, indicating differential regulation of these granzymes. However, low levels of GzmK were detected in plasma samples of healthy volunteers, which were in the same range as levels of GzmA and B. Furthermore, circulating levels of GzmK as well as of GzmA and B were significantly elevated in patients suffering from viral infections. We conclude that GzmK protein is produced by cytotoxic cells, and just as GzmA and B it can be released in a soluble form into the extracellular space. Furthermore, our data suggest that despite a more restricted cellular expression pattern, GzmK seems to participate in immune responses against several viruses.

Death by a Thousand Cuts: Granzyme Pathways of Programmed Cell Death

“…During inflammation and infection, elevated levels of granzymes exist in both serum and other bodily fluids. Examples in which extracellular granzymes have been detected include the serum of patients undergoing acute cytomegalovirus infection or chronic HIV infection, the joints of rheumatoid arthritis patients, and the bronchoalveolar lavage fluid of allergen-challenged patients with asthma and patients with chronic obstructive pulmonary disease (9,114,(179)(180)(181)(182)(183). Elevated granzyme levels also occur in the serum of patients with endotoxemia and bacteremia, supporting the idea that granzymes are expressed and secreted by activated leukocytes, not just by lymphocytes (184).…”

“…Low concentrations of GzmA, GzmB, and GzmK have been detected in the serum of healthy donors (179). During inflammation and infection, elevated levels of granzymes exist in both serum and other bodily fluids.…”

Granzymes Regulate Proinflammatory Cytokine Responses

“…However, this dogma has recently been debated, in particular for GrA and GrK (6,(9)(10)(11). Additionally, increased Gr levels in serum, plasma, synovial fluid, and/or bronchoalveolar lavage fluid have been described in patients suffering from inflammatory diseases, including rheumatoid arthritis (GrA, B), viral infections (GrA, B, K), Plasmodium falciparum infections (GrA, GrB), experimental endotoxemia or sepsis (GrA, GrB, GrK, GrM), hypersensitivity pneumonitis (GrA, GrB), and acute airway inflamma-tion (GrK) (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). These observations prompted researchers to investigate alternative Gr functions in inflammation.…”

Mouse granzyme K has pro-inflammatory potential

“…[14][15][16] (Hu)gzmK may also cleave the tumor suppressor, p53, thus sensitizing tumor cells for apoptosis induction 17 and may process a vasolin-containing protein, thus contributing to endoplasmic reticulum stress and caspase-independent cytotoxicity. 18 Compared with the proposed cytotoxic role for gzmK, the protease has been found by immunoassays 19 to be elevated in the plasma of patients with sepsis 20 and in the bronchoalveolar fluid of patients with asthma and viral pneumonias, 21 suggesting that gzmK may have additional biological functions.…”