Consequenes of an optimal spike density

Several strategies are in deveopment for vaccination with synthetic nano-particles coated with target antigens:

Our results suggest that most potent antibodies are obtained at an optimal target density.

Is evading potent antibody response an evolutionary force in setting viral spike densities?

If so, why is HIV different from other viruses?  

HIV disrupts the process of affinity maturation by depleting the helper T cell population:

The competition for reduced helper T cell signal negates the loss of competition at high spike densities:

Note that there is no structural reason preventing higher spike density on SIV, and mutant viruses with higher density have been created:

However, once injected into host the spike density goes down in subsequent generations.

Next (Summary) Outline Introduction Affinity Maturation Fitness & Evolution Optimal density Summary