New method for identifying serial killers among natural killer cells
Natural killer cells (NK cells) are an important part of our immune system: they recognize and destroy virus-infected or malignant cells - including tumour cells. There are so-called “serial killers” among the NK cells. These special natural killer cells can eliminate several diseased cells in succession. From an immunological point of view, but also in the context of tumor immunotherapies, these cells are of particular interest. However, until now it has been difficult to specifically identify these powerful immune cells and predict which natural killer cells will become serial killers.
Jens Niemann from Carsten Watzl's research team at the Leibniz research centre for Working Environment in Dortmund (IfADo) has developed a new method to identify potential serial killer NK cells. Until now, NK cells were observed microscopically when killing tumor cells and the serial killers were painstakingly counted. The newly developed procedure relies on flow cytometry and dyed antibodies.
Each time NK cells are attacked, they release substances in a process called degranulation, which cause the death of the target cell. The fact that an NK cell has degranulated can be detected by a surface protein called CD107a. By serially staining CD107a with antibodies, the researchers can now measure how often an NK cell has been active in a short period of time. Three differently colored CD107a antibodies are used and by measuring how many and which of the three dyes can be measured on the NK cell, the researchers know how often and when the NK cells have degranulated in the experiment. In this way, the potential serial killers are made visible. Using microscopic methods, identification and counting would involve considerably more effort. The new method therefore relies on flow cytometry, thereby increasing speed and throughput.
In initial tests with blood samples from healthy donors, the researchers found clear differences in the activity of the NK cells between the donors - in some individuals, up to 20 % of the cells had degranulated several times. Differences can also be found within the NK cell populations of the respective donors - these subgroups of NK cells can be analyzed much better in the flow cytometer than under the microscope. Such detailed analyses can hopefully be carried out more quickly with the new method and thus make an important contribution to the development of improved immunotherapies, for example for cancer.