Figure 6. SAA and 15-epi-LXA₄ signaling via ALX receptors regulates production of the neutrophil chemoattractant IL-8.

A549 human epithelial cells expressing human ALX receptors (A549^hALX) were exposed to BALF from HD, NSA, or SA subjects (24 hours, 37°C, 5% CO₂) and IL-8 levels were measured in the cell-free supernatant by ELISA (see Methods). (A) Mean levels of LXA₄, 15-epi-LXA₄, and SAA in BALF from n = 15 subjects used for A549^hALX cell incubations are shown in stacked bar graphs and the relative proportions are noted in pie charts. (B) IL-8 production by A549^hALX cells was measured after incubation with saline control or SAA (2.5 ng/ml or 10 ng/ml) for 24 hours. (C) IL-8 production by A549^hALX cells was measured after 24 hours of exposure to BALF from HD (n = 3), NSA (n = 6), or SA (n = 5) and is expressed as an increase relative to saline controls. Incubations with BALF without an increase in IL-8 production relative to saline control were assigned a value of zero. (D) A549^hALX epithelial cells were exposed to BALF from subjects with endogenous levels that were LXA₄^hiSAA^lo (n = 5) or LXA₄^loSAA^hi (n = 6) followed by exposure to exogenous 15-epi-LXA₄ (100 nM). Percentage inhibition of IL-8 production after 15-epi-LXA₄ exposure was calculated. *P < 0.05, ****P < 0.001 by (B) 1-way ANOVA, (C) Kruskal-Wallis test, and (D) Mann-Whitney test. ALX, airway lipoxin A₄ receptor; LXA₄, lipoxin A₄; 15-epi-LXA₄, 15-epimer lipoxin A₄; SAA, serum amyloid A; HD, healthy donors; NSA, nonsevere asthma; SA, severe asthma; IL-8, interleukin-8; BALF, bronchoalveolar lavage fluid.