A mathematical study on immune activation and related dynamics in HIV infection

Over decades, mathematical models have been applied successfully to the investigation of HIV dynamics. However, few of these investigations are able to explain the observation that host (CD4+ T) cell counts reduce, while viral load increases as the infection progresses. Various clinical studies of HIV infection have suggested that high T-cell activation levels are positively correlated with rapid disease development in untreated patients. This activation might be a major reason for the depletion of CD4+ T cells observed in most cases of long term untreated HIV infection. In this paper, we use a simple mathematical model to investigate immune activation and its role in HIV infection. Under reasonable assumptions relating to various HIV infection constants, we show that enhanced activation and reduced reversion in the immune system do result in depleted CD4+ T cell count. We further show that this process is robust to parameter variations. An extended model including viral dynamics illustrates the effects of immune activation on viral persistence and immune response. Simulations are given to verify the theoretical analysis.