  We propose a time-parameterized analogy between the thermodynamic behavior of
a 3-level energy system and the progression of the HIV infection described by
the cell population evolution generated by an appropriated cellular automata
model. The development of internal energy and its fluctuations, and of the
entropy of the 3-level energy system allows the identification of an effective
temperature that uniquely characterizes the three main stages of the dynamic
process of HIV infection. Furthermore, this thermodynamical equivalence allows
obtaining the instants associated with particular time intervals of the
evolution of internal energy and entropy, which are not quantitatively
accessible by the usual dynamic models based on differential equations or
cellular automata. The maximum entropy point, which marks the threshold between
the states of positive and negative temperatures, also corresponds to the onset
of the immune system\' exhaustion and the concomitant and inexorable
progression to AIDS. Such point lies in the time interval where the energy
inversion mechanisms in the populations of non-infected and infected cells
occur. This time lag is also characterized by considerable fluctuations of the
internal energy when different samples are compared.
