TARC stimulates platelet aggregation under low-shear conditions.

(A) Low levels of ADP (0.05 μM) stimulate TARC-induced platelet aggregation. The TARC concentration was 0.5 μg/mL, and the alternative minimal-volume aggregation assay using the Eppendorf orbital shaker was used to minimize chemokine usage (“Materials and methods”). (B) Down-regulation of the TARC response due to exposure of platelets to TARC before adding ADP (conditions as in Figure 2B). (C) Influence of prior platelet exposure to apyrase before challenge by TARC (conditions as in Figure 2C). After 10 seconds of exposure to low shear, all reactions were quenched with glutaraldehyde, and aggregation was expressed as the percentage loss in platelet singlets. Values are from 7 preparations for panels A and B and from 9 to 13 preparations for panel C. Appropriate paired or unpaired t tests were used for tests of statistical significance for the influence of apyrase. **P < .01; ***P < .001.