Role of Fcy receptors in the activation of neutrophils by soluble and insoluble immunoglobulin aggregates isolated from the synovial fluid of patients with rheumatoid arthritis

Objectives-Synovial fluid from patients with rheumatoid arthritis contains both soluble and insoluble immunoglobulin aggregates which activate reactive oxidant production in human neutrophils. The objectives were to determine the roles played by Fc-y receptors in activation of neutrophils by these complexes. Methods-Pronase treatment was used to remove Fc-yRIII from the neutrophil surface and blocking monoclonal antibodies were used to prevent the binding of complexes to Fc-yRII and FcyRIII. Results-When FcyRIII was removed from the cell surface by pronase treatment, activation by the soluble aggregates did not occur [mean (SD) inhibition 89 (16)%, n = 6] whereas activation via the insoluble aggregates was less affected [34 (16)%, n = 6]. Blocking the binding to Fc-yRIII with antibodies decreased activation in response to the soluble aggregates [mean (SD) inhibition 71 (22)%, n =8] but again had a lower effect on activation by the insoluble aggregates [40 (17)%, n = 9]. When binding to FcyRII was blocked, activation via the soluble aggregates was substantially inhibited [mean (SD) 93 (13)%, n = 8] whereas that via the insoluble aggregates was inhibited to a much lesser extent [28 (38)%, n = 9]. When Fc-yRII and III were simultaneously blocked, activation by the insoluble aggregates was only inhibited by 450/o [(19), n = 5]. Conclusion-These data thus indicate that activation ofhuman neutrophils by soluble immunoglobulin aggregates from rheumatoid synovial fluid occurs via cooperative occupancy of both Fc-yRII and III: perturbation of binding to either of these receptor classes will abrogate activation. (Ann Rheum Dis 1994; 53: 515-520) In addition to their crucial role in host defence, it is appreciated that inappropriate infiltration and activation of neutrophils into tissues can result in tissue damage in inflammatory conditions such as rheumatoid arthritis. Much evidence now exists in previous reports to suggest that neutrophil activation has occurred within synovial joints'7and hence it is of potential pharmacological interest to understand the molecular processes which activate and regulate neutrophil function within such diseased joints. The major neutrophilactivating factors within synovial fluid appear to be immune complexes/immunoglobulin aggregates8-12 which are capable of activating neutrophils via interactions with their plasma membrane Fc receptors. Neutrophils possess receptors recognising the Fc portions ofIgG and IgA`3 '4 and of these the Fcy receptors are the most clearly defined. Three types of FcyR can be present.'5 Fc-yRI (CD64) is not present on blood neutrophils but its expression is up-regulated upon exposure to cytokines such as -y-interferon'6; this receptor is also detected at low levels on neutrophils isolated from the synovial fluid of some patients with rheumatoid arthritis.5 FcyRII (CD32) and Fc-yRIII (CD 16) are both present on the surface of blood neutrophils at levels of about 7-15 000 and 100-200 000 per cell, respectively.'7 There is much debate as to the role of Fc-yRII and FcyRIII in neutrophil function. Neither of these bind monomeric IgG, but they bind dimers, trimers, immune complexes and opsonised particles. It is currently believed that FcyRIII binds complexes, but this binding does not activate phagocytosis, degranulation or the respiratory burst: Fc-yRII occupancy, however, is believed to result in neutrophil activation.'8 '9 Unlike Fc,yRII, Fc-yRIII is held on the neutrophil plasma membrane via a glycerophosphoinositol anchor which is cleaved upon activation,20 and may also be released experimentally via treatment of neutrophils with pronase, elastase and phospholipase C. We have recently shown that synovial fluid from patients with rheumatoid arthritis contains both soluble and insoluble immunoglobulin aggregates which are capable of activating reactive oxidant production by neutrophils.9 However, several lines of evidence indicate that these aggregates activate neutrophils via distinct mechanisms. Firstly, the soluble aggregates only activate neutrophils that have been primed in vivo or in vitro by GM-CSF or -y-interferon. Secondly, the soluble aggregates activate a transient (2-4 minutes) burst of oxidase function in primed cells whereas the insoluble aggregates stimulate a slower (15-20 minutes) activation in primed Department of Biochemistry, University of Liverpool, Liverpool, United Kingdom J J Robinson F Watson S W Edwards Rheumatic Diseases Unit, Royal Liverpool Hospital, Liverpool, United Kingdom R C Bucknall Correspondence to: Dr S W Edwards, Department of Biochemistry, University of Liverpool, PO Box 147, Liverpool LG9 3BX, United Kingdom. Accepted for publication 26 April 1994 515 group.bmj.com on June 29, 2017 Published by http://ard.bmj.com/ Downloaded from