The role of T-helper/T-regulator lymphocyte ratio on the adaptive immune response: a mathematical model

In this work we use a combination of statistical physics and dynamical systems approaches, to analyze the response to an antigen of a simplified model of the adaptive immune system, which comprises B, T helper and T regulatory lymphocytes. Results show that the model is remarkably robust against changes in the kinetic parameters, noise levels, and mechanisms that activate T regulatory lymphocytes. In contrast, the model is extremely sensitive to changes in the ratio between T helper and T regulatory lymphocytes, exhibiting in particular a phase transition, from a responsive to an immuno-suppressed phase, when the ratio is lowered below a critical value. To the best of our knowledge, this is the first mathematical study to support the validity of the T-helper/T-regulator lymphocyte ratio as an index of immunosuppression, with a potential for prognostic monitoring.