Persons of African ancestry, on average, have lower white blood cell (WBC) counts than those of European descent (ethnic leukopenia), but whether this impacts negatively on HIV-1 disease course remains unknown. Here, in a large natural history cohort of HIV-infected subjects we show that although leukopenia…was associated with an accelerated HIV disease course, this effect was more prominent in leukopenic subjects of European than African ancestry. The African-specific -46C/C genotype of Duffy Antigen Receptor for Chemokines (DARC) confers the malaria-resisting, Duffy-null phenotype, and we found that the recently described association of this genotype with ethnic leukopenia extends to HIV-infected African Americans (AA). The association of Duffy-null status with HIV disease course differed according to WBC but not CD4+ T cell counts, such that leukopenic but not non-leukopenic HIV+ AAs with DARC -46C/C had a survival advantage compared with all Duffy-positive subjects. This survival advantage became increasingly pronounced in those with progressively lower WBC counts. These data highlight that the interaction between DARC genotype and the cellular milieu defined by WBC counts may influence HIV disease course, and this may provide a partial explanation of why ethnic leukopenia remains benign in HIV-infected African Americans, despite immunodeficiency.
Duffy status is a highly ancestrally informative trait. This is a case where the relatively low between population variance found among humans does not apply. Rather, it seems that the Duffy null phenotype is a recent adaptation to malaria among West Africans. Because malaria has such a strong fitness implication many independent genetic adaptations have emerged, many of them with other negative side effects. On net individuals with side effects may still have higher fitness in an environment where malaria is endemic. Sometimes the net benefit is most evidence on a population wide scale, sickle-cell anemia is a deleterious homozygote which exists because of the much higher frequency of heteryzogytes vis-a-vis wild type homozygotes. Many malaria adaptations exhibit the large effect dynamic and suboptimal characteristic which one might except from the early stages of natural selection in a Fisherian model. You deal with the adaptive pressures of the present and let the future take care of itself. In this case, the future involved HIV:
The researchers found that leukopenia was generally associated with a faster disease progression from HIV to AIDS, independent of known predictors of AIDS development. “On average, leukopenic European Americans progressed nearly three times faster than their non-leukopenic African or European counterparts,” explained Hemant Kulkarni, MD, first author of this study. “However, leukopenic African Americans had a slower disease course than leukopenic European Americans, even though twice as many African Americans in the study had leukopenia.”
The investigators found that the DARC variation, not race, explained the differences in WBC counts in African Americans with HIV. Among those who were leukopenic, only those with the DARC variation experienced a significant survival benefit. Additionally, this survival advantage became increasingly pronounced in those with progressively lower WBC counts, suggesting that the interaction between DARC and WBC counts was the primary influence on slowing HIV disease progression in African Americans.
There are no doubt details in the genetic architecture of those with the null genotype worth future investigation.