Histamine-induced chemokine secretion in HUVECs. Secretion of chemokines in the absence or presence of histamine (0.1 mM, 15 minutes) was measured by ELISA, and the secretory ratio was obtained by dividing the secretion level in the presence of stimulant by the level in nonstimulated cultures. Each pair of triangles, circles, or squares represents the medians of triplicate wells from an individual HUVEC culture, comparing all responses to those of IL-8 in parallel wells of the same microtiter plate. Statistical analysis was performed by paired comparison of median secretion levels in the presence or absence of secretagogue using the Wilcoxon signed rank test. The level of significance thus obtained is given for each chemokine. The dashed line indicates a secretory ratio of 1 and absence of regulated secretion.