Question

One factor that makes it hard for pathogens and hosts to evolve "perfect" attacks or defenses is that natural selection acts on existing systems, which means that altering a system to fit a particular time and situation may make it less fit in other situations. A prime example of this is:

> VSG switching.

> All of the above.

> Somatic Recombination vs. Somatic Hypermutation.

> The CCR5 gene and the CCR5-delta32 mutation case.

Answer 1

VSG (variant-specific surface glycoprotein) switching is a response by the parasites in order to evade the host immune response as it helps in increasing viability of pathogen in the bloodstream and tissue fluids. It is a more generalized mechanism that protect the pathogen from host defenses.

Somatic hypermutation can be referred to as the adaptation of the immune system in response to the diverse kinds of pathogens it interacts with, like its observed in class switching.

Somatic recombination is the phenomemon of VDJ recombination that occurs in the B cells, in order to generate a specific response to the given antigen.

In these, the responses generated are transient and adapt as and when the situation changes so there will not be a lot of difference in the fitness of these responses in different situations.

CCR5 delta32 mutation is advantageous due to the fact that it offers resistance to Bubonic plague and HIV. The actual role of CCR5 in the cell is to allow chemokines to enter, which mediate the inflammatory response of body to injuries. Due to this mutation, other functions of the receptor get impaired, resulting in poor response in other situations (predominantly allergies or injury responses). So, this looks like a prime example of such a natural selection.

Hence, the answer is CCR5-delta32 mutation case.