Life span of lymphocytes
The lifespan of lymphocytes can vary greatly due to their different tasks: lymphocytes that never came into contact with antigens (foreign body structures) die after only a few days, while activated lymphocytes, e.g. plasma cells, can survive for about 4 weeks. The longest survival is achieved by memory cells, which can survive several years and thus contribute to the immunological memory. According to recent findings, there are also long-lived plasma cells, which produce corresponding antibodies even after the infection has subsided and thus ensure a stable antibody titer (=dilution level). A lifelong immunity is usually only achieved with live vaccines, whereby it is to be expected that an extremely small, harmless part of the vaccine remains in the organism.
What is the lymphocyte transformation test ?
The lymphocyte transformation test (LTT) is a method for the detection of special T-lymphocytes, each of which is specialized for a certain antigen (foreign body fragment). It is mainly used in immunofunction diagnostics but recently also in allergology for the detection of allergies to certain drugs or metals, which manifest themselves only with a delay. At present, it is mainly recommended as a supplement to the epicutaneous test.
This test is a provocation test to check for contact allergies. In addition, its significance as a detection test for certain pathogens such as Lyme disease is currently the subject of controversial discussion. In the first step of the lymphocyte transformation test, the lymphocytes are separated from the other blood cells by several washing processes and centrifugation (a procedure that breaks down the blood components according to their mass).
The cells are then left to grow on their own for a few days under optimal growth conditions together with the test antigen. A control sample remains without antigen. Radioactively marked thymine, a component of DNA, is added 16 hours before the analysis.
After this time, the radioactivity of the lymphocyte culture is measured and a so-called stimulation index is calculated. This provides information on whether and to what extent the T-lymphocytes are sensitive to the antigen. The test makes use of the fact that activated T-cells, which are increasingly produced from sensitized T-memory cells, are transformed or transformed in response to the corresponding antigen. As a result, they divide, which requires them to build up DNA, and therefore incorporate more radioactive thymine.