Agonist-induced adherence of equine neutrophils to fibronectin- and serum-coated plastic is CD18 dependent

Adherence to vascular endothelium and extracellular matrix proteins is a pre-requisite for neutrophil accumulation at sites of inflammation. In this study, equine neutrophil adherence to fibronectin and autologous serum-coated plastic in response to PAF, hrIL-8, hrC5a and PMA has been measured. In addition, the mechanisms involved have been investigated using monoclonal antibodies (MoAbs) against the β2 integrin CD18. PAF and hrC5a caused similar, concentration dependent, increases in adherence to fibronectin- and serum-coated plastic (maximum responses 19 ± 4% and 19 ± 3% for PAF and 15 ± 4% and 16 ± 2% for hrC5a on fibronectin- and serum-coated plastic, respectively). Adherence in response to PMA, although not reaching a maximum over the time course studied, was of a similar magnitude on the two surfaces (41 ± 1% and 38 ± 2% with 10−7 M PMA on fibronectin- and serum-coated plastic, respectively). In contrast, the maximum adherence caused by hrIL-8 was significantly lower on fibronectin- than on serum-coated plastic (9 ± 3% vs. 17 ± 2%; 10−8 M hrIL-8). Pre-incubation with MoAbs against CD18 (H20A and 6.5E) caused concentration related inhibition of stimulus-induced adherence to both fibronectin- and serum-coated plastic. Equine neutrophil adherence in response to PAF, hrIL-8, hrC5a and PMA therefore appears to be mediated by a CD18 dependent mechanism.