Abstract
It is well-known that microwaves produce both thermal and nonthermal effects. Microwave ablation can produce thermal effects to activate the body's immune system and has been widely used in cancer therapy. However, the nonthermal effects of microwaves on the immune system are still largely unexplored. In the present study, we exposed rats to multifrequency microwaves of 2.8 GHz and 9.3 GHz with an average power density of 10 mW/cm(2), which are widely used in our daily life, to investigate the biological effects on the immune system and its potential mechanisms. Both single-frequency microwaves and multifrequency microwaves caused obvious pathological alterations in the thymus and spleen at seven days after exposure, while multifrequency microwaves produced more pronounced injuries. Unexpectedly, multifrequency microwave exposure increased the number of both leukocytes and lymphocytes in the peripheral blood and upregulated the proportion of B lymphocytes among the total lymphocytes, indicating activation of the immune response. Our data also showed that the cytokines associated with the proliferation and activation of B lymphocytes, including interleukin (IL)-1α, IL-1β and IL-4, were elevated at six hours after exposure, which might contribute to the increase in B lymphocytes at seven days after exposure. Moreover, multifrequency microwave exposure upregulated the mRNA and protein expression of B cell activation-associated genes in peripheral blood. In addition to immune-associated genes, multifrequency microwaves mainly affected the expression of genes related to DNA duplication, cellular metabolism and signal transduction in the peripheral blood and spleen. In conclusion, multifrequency microwaves with 2.8 GHz and 9.3 GHz caused reversible injuries of the thymus and spleen but activated immune cells in the peripheral blood by upregulating mRNA and protein expression, as well as cytokine release. These results not only uncovered the biological effects of multifrequency microwave on the immune system, but also provide critical clues to explore the potential mechanisms.