Chemotactic activity of human blood leukocytes in plasma treated with EDTA: chemoattraction of neutrophils about monocytes is mediated by the generation of NAP-2

In slide preparations of human blood leukocytes in autologous plasma containing EDTA, many adherent monocytes are initially chemotactic for neutrophils (PMN). We have identified the che- motactic factor that they generate as neutrophil- activating peptide-2 (NAP-2), as evidenced by dis- traction of the gradient by authentic human NAP-2, the importance of platelets in the media, which elaborate the precursor of NAP-2, and sup- pression of the chemotactic response by serine protease inhibitors, which would block the mono- cyte-derived serine esterase that creates NAP-2 from its immediate precursor. Consistent with this conclusion is inhibition of the chemotactic re- sponse to monocytes by agents that block CXCR2, the receptor that NAP-2 uses. Later, when the monocyte moves from the center of chemoattrac- tion, the activated PMN themselves, whose own chemotactic properties are enhanced in EDTA/ plasma, appear to take over generation of the gra- dient, resulting in a prolonged ingress of PMN from outside the field ("second wave"). Chemoattraction by monocytes seems to be simply one way of stim- ulating the PMN, which, once activated, fail in EDTA/plasma to efficiently shut off their own che- moattraction for other PMN. We suggest that these exaggerated chemotactic effects are due to the loss of normal modulation by a regulatory factor(s) de- signed to keep the chemotactic response from get- ting out of hand—i.e., a tonic inhibitor of chemo- taxis in plasma. J. Leukoc. Biol. 72: 175-182; 2002.