  We formulate the dynamical model for the anti-tumor immune response based on
intercellular cytokine-mediated interactions with the interleukin-2 (IL-2)
taken into account. The analysis shows that the expression level of tumor
antigens on antigen presenting cells has a distinct influence on the tumor
dynamics. At low antigen presentation a progressive tumor growth takes place to
the highest possible value. At high antigen presentation there is a decrease in
tumor size to some value when the dynamical equilibrium between the tumor and
the immune system is reached. In the case of the medium antigen presentation
both these regimes can be realized depending on the initial tumor size and the
condition of the immune system. A pronounced immunomodulating effect (the
suppression of tumor growth and the normalization of IL-2 concentration) is
established by considering the influence of low-intensity electromagnetic
microwaves as a parametric perturbation of the dynamical system. This finding
is in qualitative agreement with the recent experimental results on
immunocorrective effects of centimeter electromagnetic waves in tumor-bearing
mice.
