Global solvability of a model for tuberculosis granuloma formation

TL;DR

This paper proves the global solvability of a complex nonlinear PDE system modeling tuberculosis granuloma formation, addressing mathematical challenges posed by additional positive terms in the equations.

Contribution

It establishes the existence of solutions for a novel, biologically motivated PDE model, extending previous work on chemotaxis-consumption systems.

Findings

Proved global existence of solutions in 2D and 3D domains.

Developed new a priori estimates for complex PDE systems.

Overcame challenges posed by positive terms in the equations.

Abstract

We discuss a nonlinear system of partial differential equations modelling the formation of granuloma during tuberculosis infections and prove the global solvability of the homogeneous Neumann problem for \begin{align*} \begin{cases} u_t = D_u \Delta u - \chi_u \nabla \cdot (u \nabla v) - \gamma_u uv - \delta_u u + \beta_u, \\ v_t = D_v \Delta v + \rho_v v - \gamma_v uv + \mu_v w,\\ w_t = D_w \Delta w + \gamma_w uv - \alpha_w wz - \mu_w w,\\ z_t = D_z \Delta z - \chi_z \nabla \cdot (z \nabla w) + \alpha_z f(w)z - \delta_z z \end{cases} \end{align*} in bounded domains in the classical and weak sense in the two- and three-dimensional setting, respectively. In order to derive suitable a~priori estimates, we study the evolution of the well-known energy functional for the chemotaxis-consumption system both for the $(u, v)$- and the $(z, w)$-subsystem. A key challenge compared to "pure" consumption systems consists of overcoming the difficulties raised by the additional, in part positive, terms in the second and third equations. This is inter alia achieved by utilising a dissipative term of the (quasi-)energy functional, which may just be discarded in simpler consumption systems.