The process of neutrophil migration from the bloodstream and into the inflamed extravascular tissue involves a complex interaction between the neutrophil and the adjacent
vascular endothelium, a mechanism known as the adhesion cascade. Activation of LFA-1(lymphocyte function-associated antigen-1; β2-integrin) is critical for neutrophil arrest,
allowing it to establish a tight binding to its endothelial ligand ICAM-1(intercellular adhesion molecule-1). In resting leukocytes, the β2-integrins state in “low-affinity”
conformation (inactive form). Inactive state of integrins do not show any signaling effect in cell. Previously our laboratory reported LFA-1 ligation induced ROS (reactive oxygen species) production leads to regulate VCAM-1 (vascular cell adhesion molecule-1) binding on monocytes. More recently we found, CRP (C-reactive protein) is priming agent of neutrophil respiratory burst. CRP is sensitive but non-specific marker of inflammation, normal range of CRP lower than 1mg/L in serum in healthy adult, but first 24-72 hours inflammation this number increases as much as 1000folds. CRP is ligand of FcγR, this receptor is always “ready to state” on leukocytes. Thus, we figure out, the beginning part of the inflammation CRP ligation primes neutrophil respiratory burst, generated ROS production might be modify to low-affinity form of β2-integrin in neutrophils. In present study, we found that, CRP has priming effect on respiratory burst of different types of cells (neutrophil like differentiated HL-60 and granulocytes). However LFA-1 ligation alone did not show any effect on respiratory burst of neutrophil, but incorporate with CRP, PMA (phorbol myristate acetate) induced to generate huge amount of ROS production in neutrophils. The priming mechanism of CRP transduced through phosphorylation of the cytosolic subunit p47phox, via p38MAPK pathway. However, LFA-1 ligation alone did not show any signaling
pathways, but significantly induced phosphorylation of ERK after CRP paired with PMA treatment. Finally in β2-integrin efficient binding part, we saw CRP treatment induced to
the “activation of β2-integrin” but did not change “total” expression levels of β2-integrin in dHL-60 and neutrophils. Hence we conclude that, both CRP and LFA-1 ligation
participate in generation of ROS production in “feed-back” mechanism. Low-affinity conformation of β2-integrin modulated by CRP primed ROS production, after the full
activation of β2-integrin, ligation of β2-integrin induced huge amount of ROS production in neutrophils. These results provide a novel pathway in which CRP primed ROS play
critical role in integrin cross-talk in neutrophil.

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