Dynamics of cytotoxic T-lymphocytes and helper cells in human immunodeficiency virus infection with Hill-type infection rate and sigmoidal CTL expansion

Clinical studies show intra-patient variability of real time data of host cells and virus particles in case of HIV infection. However, basic HIV models do not show oscillations unless self-proliferation of host cells is considered. Extended basic models with immune response also do not show oscillations unless delay is considered. In this study we investigate whether oscillations can be the result of immune response alone in a more realistic model in absence of delay and without self-proliferation of host cells. For this purpose, we study the interaction of host cells, virus specific T-lymphocytes and human immunodeficiency virus with generalized infection rate and sigmoidal function for CTL expansion in presence and absence of self-proliferation of helper cells. Stability and instability of both systems are determined with respect to the parameter that measures the virus replication. It is shown that an otherwise stable interior equilibrium of the system without or with self-proliferation may be unstable and show oscillations in presence of immune response. More specifically, the interior equilibrium of both systems may switch its stability more than once in presence of immune response. Our analysis indicates that immune response alone may be responsible for producing oscillations and thus exhibit intra-patient variability of host cells and virus particles in vivo non-delayed HIV models in presence or absence of self-proliferation of host cells.