Priming Interleukin 8 production - Role of platelet-activating factor and p38

Hypothesis: Platelet-activating factor (PAF) activates p38, an important in tracellular signal transduction kinase, and primes human mononuclear cells for the production of interleukin 8 (IL-8), a potent chemoattractant and ac tivator of neutrophils. Methods: Human mononuclear cells were isolated from healthy adults by Ficol l-paque density-gradient centrifugation. Interleukin-8 in the supernatant w as measured by enzyme-linked immunosorbent assay. Dual phospho-specific p38 antibody was used to detect activated p38 by Western blotting. Results: Lipopolysaccharide (LPS) and PAF activated p38. There was a shorte r latency to peak p38 activation with PAF vs LPS stimulation, 5 vs 30 minut es. Platelet-activating factor-induced p38 activation was calcium dependent because it was inhibited by ethyleneglycoltetracetic acid. Lipopolysacchar ide. 0.01 to 1.00 ng/mL, induced significant IL-8 production. Although PAF did not induce significant IL-8 production, it potentiated LPS-induced IL-8 production. Production of IL-8, in response to LPS alone or in combination with PBF, was inhibited by SB202190, a specific p38 inhibitor. Conclusions: Although LPS and PAF activated p38, only LPS induced IL-8 prod uction; PAF acted as a priming agent. It seems that p38 activation is neces sary but not sufficient for IL-8 production by human mononuclear cells. Ide ntifying and evaluating the activation state of inflammatory signal transdu ction pathways might lead to methods for controlling and preventing neutrop hil-induced tissue injury without interfering with the normal host immune r esponse.