Viral load and stochastic mutation in a Monte Carlo simulation of HIV

Viral load is examined, as a function of primary viral growth factor (Pg) and mutation, through a computer simulation model for HIV immune response. Cell-mediated immune response is considered on a cubic lattice with four cell types: macrophage (M), helper (H), cytotoxic (C), and virus (V). Rule-based interactions are used with random sequential update of the binary cellular states. The relative viral load (the concentration of virus with respect to helper cells) is found to increase with the primary viral growth factor above a critical value (Pc), leading to a phase transition from immuno-competent to immuno-deficient state. The critical growth factor (Pc) seems to depend on mobility and mutation. The stochastic growth due to mutation is found to depend non-monotonically on the relative viral load, with a maximum at a characteristic load which is lower for stronger viral growth.