Conferral of enhanced natural killer cell function by KIR3DS1 in early human immunodeficiency virus type 1 infection

Abstract

A flurry of recent reports on the role of activating and inhibitory forms of the killer cell immunoglobulin-like receptors (KIR) in natural killer (NK) cell activity against human immunodeficiency virus type 1 (HIV-1) have yielded widely divergent results. The role of the activating NK receptor encoded by the KIR3DS1 allele and its putative ligands, members of the HLA class I Bw4Ile80 cluster, in early HIV-1 disease is controversial. We selected 60 treatment-naïve adults for study from the OPTIONS cohort of individuals with early HIV-1 infection in San Francisco. We performed NK cell functional assays measuring gamma interferon (IFN-gamma) and CD107a expression by NK cells in the unstimulated state and after stimulation by the major histocompatibility complex class I-deficient 721.221 B-lymphoblastoid cell line. In addition, we measured CD38 expression (a T-cell activation marker) on T and NK cells. Persons who have at least one copy of the KIR3DS1 gene had higher IFN-gamma and CD107a expression in the unstimulated state compared to those who do not possess this gene. After stimulation, both groups experienced a large induction of IFN-gamma and CD107a, with KIR3DS1 carriers achieving a greater amount of IFN-gamma expression. Differences in effector activity correlating with KIR3DS1 were not attributable to joint carriage of HLA Bw4Ile80 and KIR3DS1. We detected a partial but not complete dependence of KIR3DS1 on the members of B*58 supertype (B*57 and B*58) leading to higher NK cell function. Possessing KIR3DS1 was associated with lower expression of CD38 on both CD8(+) T and NK cells and with a loss or weakening of the known strong associations between CD8(+) T-cell expression of CD38 mean fluorescence intensity and the HIV-1 viral load. We observed that possessing KIR3DS1 was associated with higher NK cell effector functions in early HIV-1 disease, despite the absence of HLA Bw4Ile80, a putative ligand of KIR3DS1. Carriage of KIR3DS1 was associated with diminished CD8(+) T-cell activation, as determined by expression of CD38, and a disruption of the traditional relationship between viral load and activation in HIV-1 disease, which may lead to better clinical outcomes for these individuals.

FIG. 1.

Gating strategy to identify NK cell populations and functional measurements. (A) Dead cells were excluded by using amine-reactive dye, and monocytes and B cells were excluded on the basis of CD14 and CD19 gating, respectively. CD4⁺ and CD8⁺ T cells and CD3⁻ cells were gated from the CD14- and CD19-negative lymphocyte population, and NK cells were derived from the CD3⁻ gate on the basis of the expression of CD16 and CD56. NK cells were then subdivided into CD56^bright and CD56^dim. (B) Cells positive for CD16 and CD56 were analyzed for surface expression of NKG2D, NKp46, and CD107a and intracellular expression of IFN-γ. FMO, fluorescence minus one; APC, allophycocyanin; ECD, phycoerythrin-Texas Red; FITC, fluorescein isothiocyanate.

FIG. 2.

NK cell functional activity by KIR and Bw4 gene combinations. Columns 1 and 2 refer to IFN-γ (green) or CD107a (purple) measurements in unstimulated cells and cells stimulated by coculture with the MHC class I-deficient 721.221 cell line, respectively. (A) KIR3DS1Pos refers to those who carry at least one copy of KIR3DS1. Those who are KIR3DS1 negative (KIR3DS1Neg) are homozygous for KIR3DL1. (B) 3DS1/Bw4I80+ refers to those who have the compound genotype, possessing both KIR3DS1 and Bw4Ile80, whereas those who are 3DS1/Bw4I80 negative are those who have one or the other gene (but not both) or have neither. This is the comparison used in the earliest genetic association studies, and its results were interpreted to signify synergy between the two gene products. (C) Persons who are KIR3DS1 carriers. The 3DS1+/Bw4I80− persons are those who carry KIR3DS1 but not the Bw4Ile80 gene, whereas the 3DS1/Bw4I80+ persons are those who have KIR3DS1 and also carry Bw4Ile80. This third comparison allows one to directly test if the presence or absence of Bw4Ile80 among KIR3DS1 carriers is associated with differences in NK cell functional measurements. The Mann-Whitney U test was used for comparisons because of the nonnormal distribution of the underlying data.

FIG. 3.

(A) MFI for CD38 on NK and CD8⁺ T cells, respectively, by KIR3DS1 carriage. We used an unpaired t test with the Welch correction for these comparisons. (B) Relationship of CD38 expression on NK and CD8⁺ T cells to the HIV-1 load among those who are not KIR3DS1 carriers. The Spearman rank correlation test was used for the correlation analysis. (C) Relationship of CD38 expression on NK and CD8⁺ T cells to the HIV-1 load among those who are KIR3DS1 carriers. The Spearman rank correlation test was used for the correlation analysis.