Adherence of neutrophils induces release of soluble tumor necrosis factor receptor forms.
TNF is a potent activator of neutrophil granulocytes which acts via two cell surface receptors: the p55-TNF receptor (TNF-R55) and the p75-TNF receptor (TNF-R75). The extracellular region of the receptors can be released by proteolytic cleavage and form soluble TNF-binding proteins, TNF-R55-BP and TNF-R75-BP, respectively. The phorbol ester PMA, the chemotactic peptide FMLP, and TNF were all found to induce release of TNF-R55-BP and TNF-R75-BP from neutrophils in suspension in a time- and dose-dependent manner as measured by ELISA. Exposure of neutrophils to 10 ng/ml of PMA for 60 min resulted in release of 900 pg of TNF-R55-BP and 350 pg of TNF-R75-BP per 5 million cells, corresponding to approximately 4800 receptors per cell. In addition, adherence by itself of neutrophils to fibrinogen-coated culture plates and other surfaces resulted in a release of TNF-R55-BP of the same magnitude as seen in response of neutrophils in suspension to 1 nM TNF, whereas the release of TNF-R75-BP was less pronounced. The protein kinase C inhibitors staurosporin and calphostin C inhibited both the TNF-, PMA-, and adherence-induced release of soluble forms of TNFRs. Ab to the common beta-chain of the leukocyte integrins (CD18) did not affect adherence-induced TNF-R55-BP release, indicating that non-integrin-dependent mechanisms are involved in receptor cleavage. However, cross-linking of anti-CD18 Ab (IB4) with a Fab2 fragment resulted in a decrease of specific binding of 125I-TNF to neutrophils indicating that the leukocyte integrins can modulate TNFR expression on neutrophils. Thus, adherence to a biological surface, without additional stimuli, induces release of soluble TNFR form from neutrophils. TNFR expression can be modulated by protein kinase C as well as both leukocyte integrins and non-integrin-dependent adherence mechanisms.
Lantz
M
M
Department of Medicine University Hospital, Lund, Sweden.
Björnberg
F
F
Olsson
I
I
Richter
J
J
D015703:Antigens, CD / Q000502:physiology; D018821:CD18 Antigens; D006801:Humans; D016023:Integrins / Q000502:physiology; D008970:Molecular Weight; D009504:Neutrophils / Q000166:cytology / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D018124:Receptors, Tumor Necrosis Factor / Q000737:chemistry / Q000378:metabolism*; D012995:Solubility
D015703:Antigens, CD; D018821:CD18 Antigens; D016023:Integrins; D018124:Receptors, Tumor Necrosis Factor; D011493:Protein Kinase C