Zymosan-induced leukotriene B4 generation by human neutrophils is augmented by rhTNF-alpha but not chemotactic peptide.

Tumour necrosis factor (TNF) is a mediator of inflammation that has been shown to enhance neutrophil responses to soluble and particulate stimuli. The release of leukotriene B4 (LTB4) by human neutrophils stimulated by unopsonized zymosan was measured in the presence or absence of recombinant human TNF-alpha (rhTNF-alpha) preincubation. There was a threefold increase in the LTB4 response at an optimal TNF concentration of 10(-9) M and an optimal preincubation time of 10-20 min. A similar time and dose dependency was observed for CR3 receptor expression and for the release of the secondary lysosomal granule marker, vitamin B12-binding protein. In contrast, the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (FMLP), although stimulating an increase in both CR3 receptor number and in particle phagocytosis, failed to induce an increase in LTB4 release in response to zymosan. In addition, the present study demonstrated that, unlike FMLP, the exocytotic mechanism for secondary granule release by rhTNF-alpha functioned in the absence of a rise in cytosolic free calcium. Furthermore, it was independent of changes in cyclic nucleotide concentrations and did not require an intact cytoskeleton. Thus the capacity of rhTNF-alpha to amplify the neutrophil response to zymosan through the CR3 receptor appears to be related to the amplification of post-membrane events as well as to an increase in the number of functionally active receptors.