Activation of extracellular signal-related protein kinases 1 and 2 of the mitogen-activated protein kinase family by lipopolysaccharide requires plasma in neutrophils from adults and newborns

Neutrophils er;posed to low concentrations of gram-negative lipopolysaccharide (LPS) become primed and have an increased oxidative response to a second stimulus (e.g., formyl-methionyl-leucyl-phenylalanine [fMLP]). In studies aimed at understanding newborn sepsis, me have shown that neutrophils of newborns are not primed in response to LPS, To further understand the processes involved in LPS-mediated priming of neutrophils, me explored the role of extracellular signal-related protein kinases (ERK 1 and 2) of the mitogenactivated protein kinase family, We found that LPS activated ERK 1 and 2 in cells of both adults and newborns and that activation was plasma dependent (masimal at greater than or equal to5%) through LPS binding protein. Although fibronectin in plasma is required for LPS-mediated priming of neutruphils of adults assessed by fMLP-triggered oxidative burst, it mas not required for LPS-mediated activation of ERK I and 2, LPS-mediated activation was dose and time dependent; masimal activation occurred with approximately 5 ng of LPS per mi and at 10 to 40 min, We used the inhibitor PD 98059 to study the role of ERK 1 and 2 in the LPS-primed fMLP-triggered oxidative burst. While Western blotting showed that 100 muM PD 98059 completely inhibited LPS-mediated ERK activation, oxidative response to fMLP by a chemiluminescence assay revealed that the same concentration inhibited the LPS-primed oxidative burst by only 40%. We conclude that in neutrophils, LPS-mediated activation of ERK 1 and 2 requires plasma and that this activation is not dependent on fibronectin, In addition, rye found that the ERK pathway is not responsible for the lack of LPS priming in neutrophils of newborns but may he required for 40% of the LPS-primed fMLP-triggered oxidative burst in cells of adults.