Immunocomplexes stimulate different signalling events to chemoattractants in the neutrophil and regulate L-selectin and beta 2-integrin expression differently.
Neutrophils express receptors for numerous phlogistons which, when occupied, trigger distinct signal-transduction pathways. Previous studies have shown that stimulation of neutrophils with chemoattractants induces shedding of the adhesive molecule L-selectin and increased expression of the beta 2-integrin CD11b/CD18. We determined the effect of ligation of classic, G-protein-linked chemoattractant receptors [C5a, interleukin-8 (IL-8), formylmethionyl-leucylphenylalanine (FMLP) and substance P], receptors for the Fc portion of IgG (Fc gamma receptors) and receptors for transforming growth factor beta (TGF beta) on expression of adhesive molecules by neutrophils and the stimulus-transduction mechanisms thought to mediate these changes. We were surprised to observe that occupancy of Fc gamma receptors by immunocomplexes (BSA-anti-BSA) stimulated increased expression by neutrophils of CD11b/CD18 at concentrations which did not affect L-selectin expression (EC50 9 micrograms/ml versus 350 micrograms/ml respectively, P < 0.00001, n = 5). In contrast, similar to previous studies, recombinant C5a, recombinant IL-8 and FMLP all stimulated increased expression of CD11b/CD18 (170-260% of basal, P < 0.001, n = 5) and shedding of L-selectin (56-75% reduction from basal, P < 0.001, n = 5) at similar concentrations and with similar potencies (EC50 = 2, 5, and 3 nM respectively). In contrast, neither TGF beta 1 nor, surprisingly, substance P affected expression of CD11b/CD18 or L-selectin. The regulation of expression of CD11b/CD18 or L-selectin in response to FMLP or immunocomplexes was unaffected by cytochalasin B (5 micrograms/ml) or the tyrosine kinase inhibitor tyrphostin-25 (25 microM). Although occupancy of both chemoattractant (FMLP) and Fc gamma receptors stimulated increments in the second messenger diacylglycerol, disruption of actin microfilaments by cytochalasin B enhanced diacylglycerol generation in response to FMLP but not in response to ligation of Fc gamma receptors. Moreover, both FMLP and immune aggregates provoked fluxes of intracellular Ca2+ concentration which differed with respect to both magnitude and kinetics and did not correlate well with regulation of adhesive-molecule expression. As upregulation of CD11b/CD18 is tightly linked to exocytosis of specific granules, these results suggest that shedding of L-selectin by activated neutrophils is not linked to exocytosis. These studies provide further evidence that receptors for chemoattractants and immunocomplexes on the neutrophil are linked to multiple signalling pathways.
Molad
Y
Y
Department of Medicine, New York University Medical Center, NY 10016.
Haines
K A
KA
Anderson
D C
DC
Buyon
J P
JP
Cronstein
B N
BN
D000199:Actins / Q000378:metabolism; D000936:Antigen-Antibody Complex / Q000276:immunology*; D015815:Cell Adhesion Molecules / Q000096:biosynthesis*; D002630:Chemotactic Factors / Q000378:metabolism*; D015936:Complement C5a / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D016023:Integrins / Q000096:biosynthesis*; D016209:Interleukin-8 / Q000378:metabolism; D019041:L-Selectin; D009504:Neutrophils / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D011961:Receptors, Fc / Q000378:metabolism; D015398:Signal Transduction; D013373:Substance P / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism
D000199:Actins; D000936:Antigen-Antibody Complex; D015815:Cell Adhesion Molecules; D002630:Chemotactic Factors; D016023:Integrins; D016209:Interleukin-8; D010743:Phospholipids; D011961:Receptors, Fc; D016212:Transforming Growth Factor beta; D019041:L-Selectin; D013373:Substance P; D015936:Complement C5a