Selective elimination of synovial inflammatory macrophages in rheumatoid arthritis by an Fcgamma receptor I-directed immunotoxin.
OBJECTIVE
To determine whether monocyte/macrophages from rheumatoid arthritis (RA) patients can be selectively eliminated by a toxin-conjugated antibody CD64-ricin A (CD64-RiA) directed toward the high-affinity receptor for IgG (FcgammaRI), exploiting the capacity of FcgammaRI to efficiently endocytose antibody which it has bound.


METHODS
Mononuclear cells from peripheral blood (PB) and synovial fluid (SF) obtained from RA patients were cultured in the presence of CD64-RiA. Cell death of monocyte/macrophages was measured by phenotypic changes (light-scatter patterns and CD14 and FcgammaRI expression) and apoptosis (nuclear DNA fragmentation). We then tested whether CD64-RiA-induced cell death of macrophages affected their capacity to stimulate antigen-induced lymphocyte proliferation and to secrete cytokines. Additionally, the capacity of CD64-RiA to inhibit proinflammatory activity and cartilage degradation by RA synovial tissue explants was evaluated.


RESULTS
Inflammatory macrophages from RA SF expressed elevated levels of FcgammaRI and were selectively eliminated by CD64-RiA via apoptotic cell death. Monocyte/macrophages from RA PB, which had lower levels of FcgammaRI expression, were much less affected. Induction of SF macrophage apoptosis was associated with efficient inhibition of antigen-induced lymphocyte proliferation and a reduction in tumor necrosis factor alpha (TNFalpha) release. Consistent with these effects on SF macrophages, CD64-RiA also inhibited TNFalpha production, interleukin-1beta production, and cartilage-degrading activity of RA synovial tissue explants.


CONCLUSIONS
Together, these data underscore the crucial role of synovial macrophages in RA joint inflammation and indicate that selective elimination of these cells through FcgammaRI-directed immunotoxins could be a novel approach to the treatment of RA.
University Medical Center Utrecht, Utrecht, The Netherlands. J.vanRoon@azu.nl
Joel A G
JA
van Roon
Anneke J
AJ
van Vuuren
Siska
S
Wijngaarden
Kim M G
KM
Jacobs
Johannes W J
JW
Bijlsma
Floris P J G
FP
Lafeber
Theo
T
Thepen
Jan G J
JG
van de Winkel
D000368:Aged; D000369:Aged, 80 and over; D000920:Antibody-Dependent Cell Cytotoxicity / Q000187:drug effects*; D017209:Apoptosis / Q000187:drug effects; D001172:Arthritis, Rheumatoid; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D004705:Endocytosis / Q000187:drug effects; D006801:Humans; D000922:Immunotoxins / Q000276:immunology / Q000633:toxicity*; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008875:Middle Aged; D010045:Outpatients; D017452:Receptors, IgG / Q000276:immunology / Q000378:metabolism*; D012276:Ricin / Q000276:immunology / Q000633:toxicity*; D013582:Synovial Fluid / Q000166:cytology; D013583:Synovial Membrane / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology
D000922:Immunotoxins; D017452:Receptors, IgG; D012276:Ricin