Behavior of Trajectories of a Four-Dimensional Model of HIV Infection

A model of interaction between the human immunodeficiency virus and the human immune system is considered. Equilibria in the state space of the system and their stability are analyzed, and the ultimate bounds of the trajectories are constructed. It has been proved that the local asymptotic stability of the equilibrium corresponding to the absence of disease is equivalent to its global asymptotic stability. The loss of stability is shown to be caused by a transcritical bifurcation.