Decreased functional NK cells in CXCR4 conditionally deficient mice. (A) In vitro cytotoxicity of NK cells in the bone marrow (left and middle) or spleen (right) from pIpC-treated MxCre/CXCR4^f/wt or MxCre/CXCR4^f/null mice. LDH release assay was used to measure NK lytic activity against the NK cell-sensitive YAC-1 target cells. DX5⁺ cells purified by magnetic-activated cell sorting (left) and sorted CD3⁻NK1.1⁺ NK cells (middle and right) were used as effector cells and were incubated with YAC-1 target cells at the indicated effector-to-target cell ratios (E/T) for 4 hours. Data are representative of 3 experiments; n = 3. *P < .05. (B) Flow cytometric analysis of in vitro IFN-γ production by NK cells in the spleen from pIpC-treated MxCre/CXCR4^f/wt or MxCre/CXCR4^f/null mice. Splenocytes were stimulated with IL-12 and IL-18 for 6 hours. IFN-γ production was measured in CD3⁻NK1.1⁺ NK cells by intracellular staining.