Synergies between the dynamics of the immune response of T cells and the variable structure control paradigm

Abstract

This paper argues that strong synergies exist between the Variable Structure Control (VSC) paradigm and the dynamical behaviour of the immune response of T cells following vigorous infection. Sharp changes in T cell population kinetics in response to an infection have been revealed by experimental studies. Striking similarities are shown to exist between the phase portrait of a classical VSCS and the phase portrait of an accurate model of the T cell response with an on/off activation function. The robustness properties of the T cell response dynamics described in current experimental and mathematical studies are evaluated using Lyapanov stability theory and numerical simulations. The findings demonstrate that the T cell dynamics following vigorous infection behave as a closed-loop system under variable structure control. This control law effectively determines the immunological control structure and the metabolic energy regime required to ensure that the dynamics of the responding T cells maintain a healthy state. The VSC paradigm thus provides a mechanism to understand the transition from health to disease.