Final answer:
Individuals with heterozygous HLA loci have a delayed AIDS progression due to greater immune system receptor diversity, aiding in the recognition and control of HIV.
Step-by-step explanation:
The most likely reason that HIV-infected people with heterozygous HLA loci have a delayed progression to AIDS compared with patients who are homozygous at one or more HLA loci is the increased diversity in immune system receptors that can recognize and bind to various pathogens, including different strains of HIV.
This increased genetic diversity at the HLA loci results in a broader range of antigen presentation to T cells, thereby improving the immune system's ability to target and control HIV infections. As the virus mutates, individuals with a more diverse set of HLA molecules are more likely to have at least some that can still present pieces of the virus to the immune system. This is different from individuals with homozygous HLA loci, who have less variety in antigen presentation, making it easier for the virus to evade immune detection and accelerate disease progression.