Leukocytes from CX3CR1-M280 homozygotes have defective calcium flux and chemotactic responses to FKN. PBMCs from donors homozygous for CX3CR1-WT (i.e., genotype 1 in Table 2) and CX3CR1-M280 (i.e., genotype 3 in Table 2) were used. (a) Calcium flux: kinetics. Shown are real-time fura-2 AM fluorescence traces in response to the addition of 1 μM soluble FKN (arrow). Data represent the mean ± SEM of triplicates, and are representative of four independent experiments. (b) Calcium flux: FKN concentration dependence. Shown is the maximal fura-2AM fluorescence change of PBMCs in response to the indicated concentration of FKN. Data are summarized as the mean ± SEM of results from four independent experiments, two for each CX3CR1-M280 homozygote, in which each condition was tested in triplicate. P values at the top of each set of bars compare results for CX3CR1-M280 and CX3CR1-WT by two-tailed t test. (c) Chemotaxis. PBMCs from the indicated donors were added to the top of Transwell chemotaxis chambers. Specific chemotaxis of CD56⁺ NK cells (>90% mAb 2A9–positive for all five donors) was determined in response to the indicated concentration of FKN or 10 nM SDF-1 (CXCL12). Data are summarized as the mean ± SEM of results from four independent experiments, two for each CX3CR1-M280 homozygote, in which each condition was tested in triplicate. P values at the top of each set of bars compare results for CX3CR1-M280 and CX3CR1-WT by two-tailed Student t test.