Chapter 20, Problem 4DAA

Adapting to Host Defenses Surface proteins called HLAs allow white blood cells to detect HIV particles and fight an infection. In a recent study, scientists tested whether HIV is adapting to this host defense. They did so by looking at the frequency of a specific mutation (1135X) in HIV. This “escape mutation” helps the virus avoid detection by a version of the HLA protein (HLA-B*51) that is common in some regions of the world, but not in others. FIGURE 20.19 shows the percentage of HIV-positive people who had HIV with the 1135X mutation. Data were collected at medical centers from several parts of the world.

FIGURE 20.19 Regional variation in the frequency of the 1135X escape mutation among HIV-positive people. For each region, pink bars represent the percentage of people whose blood cells have HLA-B*51. and thus cannot detect 1135X mutants. Blue bars represent the percentage of people with other versions of the HLA protein. These people have blood cells that can detect and fight HIV even if it has the 1135X mutation.

4. Japan has a high frequency of HLA-B*51; about half the population has it. How might this explain the high frequency of the 1135X mutation in Japanese with other HLAs?