Natural killer cells are key cells of the immune system that belong to the innate immunity branch and defend the system against pathogens and tumour cells with their cytotoxicity. Natural killer cells link adaptive immunity to innate immunity by releasing pro-inflammatory cytokines into the environment upon activation, which then activate other cells of the immune system. Through their cytotoxicity, natural killer cells ensure that threats in the system are eliminated. They contain secretory granules consisting of a series of cytolytic molecules, such as granzymes (A, B, H, K, M), perforin and granulysin. They are released into the cytosol of the target cell by degranulation and induce apoptosis. One of the most important molecules found in secretory granules and a major mediator of cell death in target cells is granzyme B.
Granzyme B is a serine protease that is found as an inactive enzyme in the secretory granules of natural killer cells. Upon activation of the cell, the granules with granzyme B, perforin and other molecules, are released into the cytosol of the target cell by exocytosis. A cascade of events takes place in the cytosol, leading to the assembly of a complex called the apoptosome and the initiation of cell death. Granzyme B not only plays a role in cell death, but its increased concentration in the extracellular matrix has been found in various autoimmune diseases. In future, granzyme B could become an important biomarker both for predicting the progression of various autoimmune diseases and for the prediction of immunotherapy treatments success.
In this thesis, we tested the in vitro detection of granzyme B with a fluorescent substrate and demonstrated increased proteolytic activity in a coculture of natural killer cells and tumour cells. Granzyme B expression in coculture was detected by immunodetection after Western transfer.
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