CHEMOTAXINS C5A AND FMLP INDUCE RELEASE OF CALPROTECTIN (LEUKOCYTE L1PROTEIN) FROM POLYMORPHONUCLEAR CELLS IN-VITRO

Aims - To determine whether the chemotaxins C5a and formylpeptide (fML P) can stimulate the release of calprotectin, the major leucocyte prot ein of polymorphonuclear neutrophils (PMN). Methods - A dose response curve for the uptake of I-125 labelled rC5a and fMLP in PMN was determ ined by radioimmunoassay. The unlabelled chemotaxins were then incubat ed with FMN and the concentration of calprotectin in PMN lysates and s upernatants was measured by an enzyme immunoassay. Results - Both rC5a and fMLP induced release of calprotectin from PMN in a dose dependent manner as determined by a reduction in intracellular calprotectin con centration. A minimum of similar to 10% of total PMN calprotectin was retained at concentrations of 10-100 nM of rC5a and 0.1-10.0 nM of fML F. Antibodies to C5a reduced the rC5a mediated release of calprotectin , and the fMLP antagonist N-t-Boc-MLP inhibited the fMLP induced calpr otectin release. Because receptors for rC5a (CD88) and fMLP are G prot ein coupled and thought to be pertussis toxin sensitive, PMN were incu bated with this toxin before the experiments. The toxin was found to r educe uptake of rC5a by the cells and to inhibit rC5a and fMLP mediate d calprotectin release. Conclusions - rC5a and fMLP mediate release of calprotectin from PMN in vitro. This effect might be important during human infections in vivo.