Neutrophil Activation on Biological Surfaces

Recombinant tumor necrosis factor alpha (rTNFa) and beta (rTNF#) did not trigger H202 release from PMN in suspension. However, when PMN were plated on polystyrene surfaces coated with serum, fibronectin, vitronectin, laminin, or human umbilical vein endothelial cells (HUVEC), rTNFs induced a massive, prolonged secretory response, similar to that elicited by phorbol myristate acetate (PMA) or bacteria. On serum-coated plates, the maximum sustained rate of H202 release in response to rTNFa was 2.6±0.2 nmol/min per 106 PMN, the same as that with PMA; release continued for 73±4 min. On laminin-coated surfaces or HUVEC, release of H202 in response to rTNFs was slower, but lasted 3.5 h, reaching the same total (> 100 nmol/106 PMN). Not only was this response far longer and larger than for other soluble stimuli of the respiratory burst studied with PMN in suspension, but the concentration necessary to elicit a half-maximal response (EC50) for rTNFa was orders of magnitude lower (55 pM). Responses were similar with FMLP, but ranged from zero to small with recombinant IFNa, recombinant IFN#,, recombinant IFN'y, platelet-derived growth factor, recombinant IL-1#, or bacterial lipopolysaccharide. Adherent monocytes did not secrete H202 in response to rTNFs. H202 secretion by adherent PMN was first detectable 15-90 min after addition of rTNFs or FMLP. This lag period was unaffected by prior exposure ofPMN to rTNFa in suspension, by allowing PMN to adhere before adding rTNFa, or by incubating adherent PMN in medium conditioned by rTNFa-treated PMN. Cytochalasins abolished H202 secretion in response to rTNFs, but not FMLP, if added during, but not after, the lag period. Thus, H202 secretion from rTNFa-treated PMN appears to be a direct but delayed response that requires assembly of microfilaments during exposure to the cytokine. These results suggest that PMN adherent to intraor extravascular surfaces may undergo a massive, prolonged respiratory burst at the command of macrophages and lymphocytes reacting to microbial products and antigens.