Global solvability of a model for tuberculosis granuloma formation

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 Δu - χ_u \nabla \cdot (u \nabla v) - γ_u uv - δ_u u + β_u, \ v_t = D_v Δv + ρ_v v - γ_v uv + μ_v w,\ w_t = D_w Δw + γ_w uv - α_w wz - μ_w w,\ z_t = D_z Δz - χ_z \nabla \cdot (z \nabla w) + α_z f(w)z - δ_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.