We have shown previously IL-8 accumulation into skin blisters of normal humans and that exudative neutrophils may play an important autocrine role in the recruitment of additional neutrophils to inflammatory sites in vivo. Compared with human peripheral blood cells, exudative neutrophils have greatly increased stores of the neutrophil chemoattractant IL-8 but the mechanism for the increase in neutrophil IL-8 during exudation is not defined. Last year we showed that treatment of peripheral blood neutrophils with either the chemotactic peptide fMet-Leu-Phe (fMLF) or leukotriene B4 (LTB4) alone, or fibrinogen alone, results in little increase in the production of IL-8 by peripheral blood neutrophils. However, a chemotactically active dose of fMLF or LTB4 in the presence of a physiological concentration of fibrinogen results in synergistic (200 fold) induction of IL-8 and protein synthesis. The levels of IL-8 obtained are comparable to those observed in exudative cells. This year we showed that peripheral blood human monocytes treated with fibrinogen and the chemoattractant C5a results in a 150 fold increase in IL-8. The increase is mediated through the toll-like receptor 4 pathway as evidenced by greatly reduced response in patients with mutations in this pathway and by inhibition of the response with an antibody (MY-4) against CD14, a toll-like receptor 4-associated LPS receptor.
