  An investigation was conducted to study the robustness of the results
obtained from the cellular automata model which describes the spread of the HIV
infection within lymphoid tissues [R. M. Zorzenon dos Santos and S. Coutinho,
Phys. Rev. Lett. 87, 168102 (2001)]. The analysis focussed on the dynamic
behavior of the model when defined in lattices with different symmetries and
dimensionalities. The results illustrated that the three-phase dynamics of the
planar models suffered minor changes in relation to lattice symmetry variations
and, while differences were observed regarding dimensionality changes,
qualitative behavior was preserved. A further investigation was conducted into
primary infection and sensitiveness of the latency period to variations of the
model's stochastic parameters over wide ranging values. The variables
characterizing primary infection and the latency period exhibited power-law
behavior when the stochastic parameters varied over a few orders of magnitude.
The power-law exponents were approximately the same when lattice symmetry
varied, but there was a significant variation when dimensionality changed from
two to three. The dynamics of the three-dimensional model was also shown to be
insensitive to variations of the deterministic parameters related to cell
resistance to the infection, and the necessary time lag to mount the specific
immune response to HIV variants. The robustness of the model demonstrated in
this work reinforce that its basic hypothesis are consistent with the
three-stage dynamic of the HIV infection observed in patients.
