Joe Has Been HIV Positive for the Past 6 Years

Multiple Choice

Joe has been HIV positive for the past 6 years. His disease has been slowly progressing. Mike, his only partner for the past 3 years, is free of the disease. A plausible explanation for Mike's lack of infection would be

A) His CD4/CD8 ratio is probably greater than 2
B) He has a high concentration of NK cells that kill the virus
C) He lacks the coreceptor CXCR4
D) He has built up a high titer of anti-GP160 antibody