In vivo administration of α₄ integrin neutralizing mAb promotes NK-cell mobilization from the BM sinusoids. Mice were treated with an α₄ integrin neutralizing mAb for 3 hours, and BM sinusoidal NK cells were labeled by intravenous injection of 1 μg of DX5-PE mAb. Mice were killed after 2 minutes and BM cells were isolated and stained with anti-NK1.1–, anti-CD3ϵ–, and anti-KLRG1–specific mAbs. (A) Histograms show the numbers of CD3⁻/NK1.1⁺ NK cells in the BM parenchyma (DX5⁻ cells) and sinusoids (DX5⁺ cells) of untreated (−) or treated (+) mice. Each dot represents the number of BM NK cells from individual animals analyzed in independent experiments. (B) Histograms show the number ± SD of sinusoidal (DX5-PE⁺) cells evaluated within KLRG1⁻, KLRG1⁺/CX3CR1-GFP⁻ and KLRG1⁺/CX3CR1-GFP⁺ BM NK-cell subsets. Student t test was performed to compare untreated versus treated mice. *P < .05. (C) Dot plots show the reduction of KLRG1⁺/CX3CR1-GFP⁺ NK cells in anti-α4 integrin neutralizing mAb-treated mice compared with control mice. Numbers in dot plots indicate the percentage of the KLRG1⁺/CX3CR1-GFP⁺ NK cells (gated on CD3⁻/NK1.1⁺ cells). (D) Histogram overlay shows α4 expression on parenchymal (DX5⁻) and sinusoidal (DX5⁺) BM NK cells from 1 representative experiment of at least 3 performed.