Galectin-3 and soluble fibrinogen act in concert to modulate neutrophil activation and survival: involvement of alternative MAPK pathways.

Galectin-3 (Gal-3), a member of a family of highly conserved carbohydrate-binding proteins, has recently emerged as a novel cellular modulator at inflammatory foci. Here we investigated the effects of Gal-3 on central effector functions of human neutrophils, including phagocytosis, exocytosis of secretory granules, and survival. We examined the effects of Gal-3 alone or in combination with soluble fibrinogen (sFbg), an extracellular mediator that plays a key role during the early phase of the inflammatory response through binding to integrin receptors. In addition we evaluated the intracellular signals triggered by these mediators in human neutrophils. Human neutrophils incubated with recombinant Gal-3 alone increased their phagocytic activity and CD66 surface expression. In contrast to the known antiapoptotic effect of Gal-3 on many cellular types, Gal-3 enhanced PMN apoptotic rate. Preincubation with Gal-3 primed neutrophils to the effects of sFbg, resulting in a synergistic action on degranulation. On the other hand, Gal-3 and sFbg had opposite effects on PMN survival, and the simultaneous action of both agonists partially counteracted the proapoptotic effects of Gal-3. In addition, although sFbg induced its effects through the activation of the ERKs, Gal-3 led to p38 phosphorylation. Disruption of this signaling pathway abrogated Gal-3-mediated modulation of neutrophil degranulation, phagocytosis, and apoptosis. Together, our results support the notion that Gal-3 and sFbg are two physiological mediators present at inflammatory sites that activate different components of the MAPK pathway and could be acting in concert to modulate the functionality and life span of neutrophils.