Soluble Granzymes Are Released during Human Endotoxemia and in Patients with Severe Infection Due to Gram‐Negative Bacteria

Abstract

Extracellular release of granzymes is considered to reflect the involvement of cytotoxic T lymphocytes and NK cells in various disease states. To obtain insight into granzyme release during bacterial infection, granzyme levels were measured during experimental human endotoxemia and in patients with melioidosis, a severe infection due to gram-negative bacteria. Plasma concentrations of granzyme A (GrA) and GrB increased transiently after endotoxin administration, peaking after 2-6 h. In patients with bacteremic melioidosis, GrA and GrB levels were elevated on admission and remained high during the 72-h study period. In whole blood stimulated with heat-killed Burkholderia pseudomallei, neutralization of tumor necrosis factor, interleukin-12, or interleukin-18 inhibited granzyme secretion, which was independent of interferon-gamma. Stimulation with endotoxin and other gram-negative and gram-positive bacteria also strongly induced the secretion of granzymes, suggesting that granzyme release is a general immune response during bacterial infection. The interaction between the cytokine network and granzymes may play an important immunoregulatory role during bacterial infections.

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

“…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). In fact, in sepsis patients, not only is serum GzmK elevated, but its natural inhibitor (inter-α protein) is depleted, so the free active form of the enzyme is circulating and may cause damage (185).…”

Granzymes Regulate Proinflammatory Cytokine Responses

“…Alternatively, Grs could be actively secreted during inflammation. GrA and GrB are released upon LPS injection into healthy human volunteers and upon incubation of wholeblood cultures with LPS or bacteria (19), suggesting that purposeful degranulation may occur in the absence of cytotoxicity. Alternatively, secretion of Grs may take place independently from degranulation, because significant amounts of GrA and GrB continue to be secreted from cytotoxic lymphocytes in the absence of continued stimulation by antigenic cells (55).…”

“…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.…”

Extracellular Matrix Remodeling by Human Granzyme B via Cleavage of Vitronectin, Fibronectin, and Laminin

“…Plasma granzymes are also elevated during viral infections (human immunodeficiency virus-1, Epstein-Barr virus) and certain bacterial infections (16,18,19). These extracellular granzymes may arise via constitutive (nonspecific) secretion after CLs degranulate (20) or may escape the immunological synapse as the CL degranulates, disengages, and moves onto another target (21,22).…”