Optimal spike density for Affinity Maturation

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.

Synthetic vaccines

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

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

The low spike density of HIV may have evolved because of the effects of T helper cell depletion on affinity maturation

A. Amitai, A.K Chakraborty, and M. Kardar, PLOS Computational Biology (2018) (off-line)

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