Abstract
HIV-exposed uninfected (HEU) infants have higher rates of severe and fatal infections compared with HIV-unexposed (HUU) infants, likely due to immune perturbations. We hypothesized that alterations in natural killer (NK) cell activity might occur in HEU infants and predispose them to severe infections. Case-control study using cryopreserved peripheral blood mononuclear cells (PBMCs) at birth and 6 months from HEU infants enrolled from 2002 to 2009 and HUU infants enrolled from 2011 to 2013. NK cell phenotype and function were assessed by flow cytometry after 20-h incubation with and without K562 cells. The proportion of NK cells among PBMCs was lower at birth in 12 HEU vs. 22 HUU (1.68 vs. 10.30%, p < 0.0001) and at 6 months in 52 HEU vs. 72 HUU (3.09 vs. 4.65%, p = 0.0005). At birth, HEU NK cells demonstrated increased killing of K562 target cells (p < 0.0001) and increased expression of CD107a (21.65 vs. 12.70%, p = 0.047), but these differences resolved by 6 months. Stimulated HEU NK cells produced less interferon (IFN)γ at birth (0.77 vs. 2.64%, p = 0.008) and at 6 months (4.12 vs. 8.39%, p = 0.001), and showed reduced perforin staining at 6 months (66.95 vs. 77.30%, p = 0.0008). Analysis of cell culture supernatants indicated that lower NK cell activity in HEU was associated with reduced interleukin (IL)-12, IL-15, and IL-18. Addition of recombinant human IL-12 to stimulated HEU PBMCs restored IFNγ production to that seen in stimulated HUU cultures. NK cell proportion, phenotype, and function are altered in HEU infants. NK cell cytotoxicity and degranulation are increased in HEU at birth, but HEU NK cells have reduced IFNγ and perforin production, suggesting an adequate initial response, but decreased functional reserve. NK cell function improved with addition of exogenous IL-12, implicating impaired production of IL-12 by accessory cells. Alterations in NK cell and accessory cell function may contribute to the increased susceptibility to infection in HEU infants.
Highlights
HIV-exposed uninfected (HEU) infants represent a large and growing population with unique health-care needs
The infants studied at birth and 6 months were distinct, with the exception of 4 HEU infants and 4 HIV-unexposed uninfected (HUU) infants who were studied at both time points
Similar to other immunology studies that have been performed in HEU infants, it is not possible to distinguish whether the Natural killer (NK) cell perturbations that we identified result from exposure to HIV itself versus exposure to drugs, maternal co-infections, or other factors associated with maternal HIV infection
Summary
HIV-exposed uninfected (HEU) infants represent a large and growing population with unique health-care needs. Compared with HIV-unexposed uninfected (HUU) infants, HEU infants are at increased risk of morbidity and mortality from lower respiratory tract infections (LRTI), sepsis, and gastrointestinal infections [1,2,3,4,5]. HEU infants acquire lower levels of maternal antibodies during gestation [19,20,21] and demonstrate numerous perturbations of their own immune system. These perturbations likely contribute to the increased susceptibility to infection and decreased vaccine responses in HEU infants
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