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Edition No. 10 August 1996
The reaction of human T-lymphocytes (Jurkat) to high-frequency electromagnetic fields

Dr. Rainer Meyer, Dr. Frank Gollnick,
Dr. Stephan Wolke, Gabi Conrad, Hanne Bock
Physiologisches Institut der Rheinischen-Friedrich-Wilhelms-Universität Bonn, Wilhelmstr. 31, 53111 Bonn

The reaction of T-lymphocytes to electromagnetic fields has been investigated frequently. Mostly the interaction of the fields with the signal transduction cascade of immune stimulation of lymphocytes was studied. Immune stimulation of T-lymphocytes starts with binding of an antigenic molecule to the T-cell receptor complex at the outer surface of the cell membrane. This binding induces the signal transduction cascade, starting at the cell membrane and finally leading to secretion of interleukin molecules and cell division. An early step of this transduction chain is a rise in intracellular calcium concentration, [Ca 2+]i. Earlier investigations showed, that this rise may be sensitive to extremely low frequent electric and magnetic fields. In these investigations 50 Hz and 60 Hz fields have been applied. Aim of this project was to investigate the effects of pulsed high-frequency fields on the [Ca 2+]i in a T-cell line, Jurkat cells. Frequencies and pulsation pattern of the fields were tuned according to the GSM-standard of mobile communication, 900 and 1800 MHz, pulsed at 217 Hz with 14% duty cycle. The field strength was restricted to the range in which heating of the preparation does not take place. The pulsed high-frequency fields were applied in a Transversal-Electro-Magnetic-cell, TEM-cell, designed to allow microscopic observation of the cells during the presence of the high-frequency fields. The exposure system consisted of an UHF power signal generator with the facility for external modulation, a custom- designed signal generator to deliver the pulsation pattern, and a cubic TEM-cell with 7 cm The reaction of T-lymphocytes to electromagnetic fields has been investigated frequently. Mostly the interaction of the fields with the signal transduction cascade of immune stimulation of lymphocytes was studied. Immune stimulation of T-lymphocytes starts with binding of an antigenic molecule to the T-cell receptor complex at the outer surface of the cell membrane. This binding induces the signal transduction cascade, starting at the cell membrane and finally leading to secretion of interleukin molecules and cell division. An early step of this transduction chain is a rise in intracellular calcium concentration, [Ca 2+]i. Earlier investigations showed, that this rise may be sensitive to extremely low frequent electric and magnetic fields. In these investigations 50 Hz and 60 Hz fields have been applied. edge length and a usable frequency range of up to 2 GHz. Inside the TEM-cell is an open experimental chamber with a volume of 200 µl filled with the cellsuspension. The bottom of the experimental chamber consists of a glass cover slip sandwiched with a wire mesh, which is connected to the external conductor of the TEM-cell. This construction allows microscopic observation of the cells without disturbing the field inside the TEM-cell. In addition, the wire mesh closes the TEM-cell for the high-frequency fields inside. Nevertheless, the field lines converge to the wires which causes local inhomogeneities of the field strength. For both carrier frequencies applied, 900 MHz and 1800 MHz, Specific Absorption Rates (SAR-values) were calculated taking the pulsation pattern into account. A temporal and three-dimensional average of the SAR results in 15.4 mW/kg for 900 MHz and 13.5 mW/kg for 1800 MHz. According to local inhomogeneities SAR-values may vary by one order of magnitude around the stated average values depending on the position of an individual cell in the experimental chamber.

The [Ca 2+]i in the cultured human T-cells was measured by means of the fluorescent indicator dye fura-2. The fura-2 fluorescence was quantified applying digital image analysis. The experiments were designed in three phases: The first phase consisted of 500 seconds of sham exposure, followed by a second phase with 500 seconds of field exposure and a third phase where an anti-CD3 antibody was applied as chemical stimulus. The antibody should induce a rapid rise in [Ca 2+]i. The chemical stimulation served as positive control. It is an indication for the ability of the cells to generate calcium transients, thus indicating that the nonappearance of calcium transients is not due to an inability of the cells to generate those. Experiments, during which cells were exposed to the field were always carried out alternating to those, during which cells were sham exposed.

Evaluation of the experiments was carried out in two different ways:

  1. The number of cells exhibiting calcium oszillations during the different phases of an experiment was counted.
  2. The corresponding [Ca 2+]i data points of all individual cells were averaged in each experimental group and plotted as function of time.

1272 cells were investigated during this study. There was no difference in the behaviour of the cells inside or outside the TEM-cell, i.e. 74% of the cells showed spontaneous calcium oscillations. 67% of the cells responded with a rise in [Ca 2+]i to the stimulation with the antibody. During the experiments testing 900 MHz fields 449 cells were exposed and compared to 384 sham exposed cells. In the case of 1800 MHz 237 cells were exposed and compared to 202 sham exposed cells. The number of cells with calcium oscillations during exposure to the 900 MHz field was not different from that during sham exposure. In the case of 1800 MHz fields 17.7% of cells started calcium oscillations during exposure, whereas only 10.9% of cells started calcium oscillations during sham exposure. This might indicate an increase in calcium oscillations due to the field exposure.

Evaluation of the averaged [Ca 2+]i showed a small increase in [Ca 2+]i soon after the field had been switched on. This increase was present in both exposed groups, 900 and 1800 MHz, but it was not visible in any of the sham exposed groups.

Whether this small rise in [Ca 2+]i in the exposed groups is an accidential event, an artifact of the experimental setup or a real effect of the field, cannot be decided on the data base presented here. Comparable small changes have also been detected by our group in experiments testing the influence of extremely low-frequency, 50 Hz, magnetic fields. But they were not reproducable. This leads to the conclusion that the reason for the small rise in [Ca 2+]i cannot doubtless be given on this data base. The field exposure is not necessarily the reason for the observed small effects.

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