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 lipopolysacchar ide (LPS) become primed and have an increased oxidative response to a secon d stimulus (e.g., formyl-methionyl-leucyl-phenylalanine [fMLP]). In studies aimed at understanding newborn sepsis, me have shown that neutrophils of n ewborns are not primed in response to LPS, To further understand the proces ses involved in LPS-mediated priming of neutrophils, me explored the role o f extracellular signal-related protein kinases (ERK 1 and 2) of the mitogen activated 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. Altho ugh fibronectin in plasma is required for LPS-mediated priming of neutruphi ls of adults assessed by fMLP-triggered oxidative burst, it mas not require d for LPS-mediated activation of ERK I and 2, LPS-mediated activation was d ose 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 LP S-mediated ERK activation, oxidative response to fMLP by a chemiluminescenc e assay revealed that the same concentration inhibited the LPS-primed oxida tive burst by only 40%. We conclude that in neutrophils, LPS-mediated activ ation of ERK 1 and 2 requires plasma and that this activation is not depend ent on fibronectin, In addition, rye found that the ERK pathway is not resp onsible for the lack of LPS priming in neutrophils of newborns but may he r equired for 40% of the LPS-primed fMLP-triggered oxidative burst in cells o f adults.