An immune response is triggered by the invasion of a physical agent and it is characterized by the appearance of circulating antibodies (humoral immunity), and the emergence of immunologically committed cells (cellular immunity). Recognition of the intruding agent is accomplished by the antibodies (produced by lymphocytes), and the subsequent phagocytic activity is carried out by neutrophils, monocytes, and macrophages. Thus, both humoral and cellular mechanisms are intimately meshed in the functioning of the immune-response system.
One of the fundamental roles of the immune system is to protect the host from bacterial infection. Both high- and low-frequency EMFs have been shown capable of impairing resistance to infection (18, 19). Szmigielski et al. (18) studied the action of an EMF on the granulopoietic reaction in rabbits that had been subjected to an acute staphylococcal infection. Rabbits were exposed to 3000 µW/cm2, 3 GHz, 6 hours/day, for 6 or 12 weeks, and then were infected intravenously with S. aureus Wacherts. Four to six days after infection the 6-weeks exposed animals displayed stronger granulocytosis than did the control animals, but this was reversed by the end of the observation period (Fig. 7.2A). These changes were accompanied by a consistent reduction in the bone-marrow reserve pool (Fig. 7.2B), and a depressed Iysozyme activity (Fig. 7.2C). Animals exposed for 3 months displayed consistently depressed granulocytosis after the staph infection (Fig. 7.2A), and both the bone-marrow reserve pool and the blood serum Iysozyme activity were lowered during the entire postinfection period (Fig. 7.2B and C). The results were interpreted to mean that the EMF-exposed animals lacked the reserve capacity to adapt to the infection as efficiently as the control animals: fewer granulocytes could be mobilized, and there was a resulting decline in Iysozyme activity. In related in vitro studies, rabbit granulocytes were exposed to 1000-5000 µW/cm2 for 15-60 minutes to assess the effect on the cell membrane (20). An increase in the number of dead cells and a rise in the liberation of Iysosomal enzymes were found.
Fig. 7.2. Granulopoietic reaction in infected rabbits exposed to an EMF.
A 200 gauss, 50 Hz EMF also altered the natural resistance to infection (19). Following EMF exposure, mice were injected intraperitoneally with various concentrations of Listeria. The initial cell concentration required to kill half the animals was about one-fifth of that which produced the same killing effect in the controls. Additionally, the exposed animals exhibited more extensive bacterial growth in the Iymph nodes, liver, and spleen, and the phagocytic activity of their blood cells was decreased.
There are several reports of altered phagocytic capability in animals exposed to high-frequency EMFs (21-24). When rats were exposed intermittently over a 6-month period to a pulsed EMF it was reported that neutrophil phagocytic activity and blood-plasma bacteriocidal activity (determined using agar cultures of E. coli) were both decreased (21). Similar results were seen following the exposure of rats to 100 and 2250 v/m, at 14.88 MHz (22): at both field strengths, there was a marked increase in phagocytic activity of the neutrophils during the first month's exposure followed by a prolonged period of inhibited activity which lasted until the end of the 10-month exposure period.
Shandala and Vinogradov also studied the effect of an EMF (1-500 µW/cm2, 2.4 GHz, for 30 days) on the phagocytic action of neutrophils in peripheral blood (23). Using guinea pigs, they found that the percent of killed microbes increased following exposure to 1-10 µW/cm2; and decreased at 50 and 500 µW/cm2; the most pronounced effects occurred at 1 µW/cm2 . EMF-induced alterations in the complement titer in blood serum were also found. Both immunological indicators returned to normal within two months of the cessation of irradiation. A similar inhibition of antibody production was found in rabbits following exposure at 50 µW/cm2 (25).
In later studies, Shandala et al. reported a significant disturbance in the immunological system of rats exposed intermittently to 500 µW/cm2 for 30 days (26): blast cells in peripheral blood, and the rosette-forming cells in the spleen and thymus were both altered following EMF exposure.
EMFs have been reported to alter the response of immunocompetent Iymphocytes (27, 28). Mice, exposed intermittently to 500 µW/cm2 2.95 GHz for 6 and 12 weeks, were challenged with an injection of sheep red blood cells and the immune response was characterized by the number of Iymphocytes and plasmocytes in the Iymph nodes. In the 6-weeks exposed animals, the time course of the antibody-forming cells population was significantly different from that of the controls; the maximum difference occurred 6-8 days after injection of the antigen, and the effect was no longer observed after 20 days (27). Exposure for 12 weeks prior to injection resulted in no difference in immune response as compared to the controls, indicating that the mice had become adapted to the field.
The immunological reaction of guinea pigs exposed to an atmosphere of formaldehyde or carbon monoxide was altered when the animals were pretreated for 1 month with an EMF (5-50 µW/cm2, 2.4 GHz, 7 hr./day, for 1 mo.) (28).
B-lymphocytes (responsible for humoral antibody synthesis) and neutrophils are each derived from bone-marrow stem cells. Czerski et al. reported that guinea pigs subjected to a pulsed EMF (2.9 GHz, 1000 µW/cm2, 4 hr./day for 14 days) exhibited an abnormal circadian rhythm of bone-marrow stem-cell mitoses (30). In a comparable study involving guinea pigs, it was found that the EMF altered megakaryocytic activity in the bone marrow (29); it stimulated increased levels of megakaryocyte destruction, and a compensatory proliferation of megakaryoblasts.
Inflammation is a local response of vascular tissue to irritation or injury; it involves the passage of fluid containing WBCs and proteins from the blood into the tissues. This nonspecific protective response was found to be susceptible to an EMF (31). An aseptic inflammation in the peritoneal cavity of mice was induced by the implantation of a glass slip; in the resulting foreign-body reaction the glass became covered with a cell monolayer, but this response was delayed in mice that had been exposed to DC magnetic field of 600-3800 gauss.
Since 1976, investigators at Battelle Laboratories have consistently failed to observe 60-Hz biological effects in many areas including the cardiovascular, hematological and immune-response systems (32).