Minimal contribution of cell-bound antibodies to the immunoscintigraphy of inflamed joints with ^99mTc-anti-CD4 monoclonal antibodies

Summary

Aim: The cellular joint infiltrate in rheumatoid arthritis patients is rich in CD4-positive T-helper lymphocytes and macrophages, rendering anti-CD4 monoclonal antibodies (mAbs) suitable for specific immunoscintigraphy of human/ experimental arthritis. Following intravenous injection, however, mAbs are present both in the free form and bound to CD4-positive, circulating monocytes and T-cells. Thus, the present study aimed at analyzing the relative contribution of the free and the cell-bound component to the imaging of inflamed joints in experimental adjuvant arthritis (AA). Methods: AA rat peritoneal macrophages or lymph node T-cells were incubated in vitro with saturating amounts of ^99mTc-anti-CD4 mAb (W3/25) and injected i.v. into rats with AA. Results: In vitro release of ^99mTc-anti-CD4 mAb from the cells was limited (on average 1.57%/h for macrophages and 0.84%/h for T-cells). Following i.v. injection, whole body/joint scans and tissue measurements showed only negligible accumulation of radioactivity in inflamed ankle joints (tissue: 0.22 and 0.34% of the injected activity, respectively), whereas the radioactivity was concentrated in liver (tissue: 79% and 71%, respectively), kidney, and urinary bladder. Unlike macrophages, however, anti-CD4 mAb-coated T-cells significantly accumulated in lymphoid organs, the inflamed synovial membrane of the ankle joints, as well as in elbow and knee joints. Conclusion: While the overall contribution of cell-bound mAbs to the imaging of arthritic joints with anti-CD4 mAbs is minimal, differential accumulation of macrophages and T-cells in lymphoid organs and the inflamed synovial membrane indicates preferential migration patterns of these 2 cell populations in arthritic rats. Although only validated for ^99mTc-anti-CD4 mAbs, extrapolation of the results to other anticellular mAbs with similar affinity for their antigen may be possible.

Zusammenfassung

Ziel: Das zelluläre Gelenkinfiltrat von Patienten mit rheumatoider Arthritis ist reich an CD4-positiven T-Helfer- Lymphozyten und Makrophagen. Dies macht monoklonale Anti-CD4-Antikörper (Anti-CD4-mAk) für die spezifische Immunoszintigraphie von humaner/experimenteller Arthritis geeignet. Nach intravenöser Injektion liegen mAk sowohl in freier Form als auch gebunden an CD4-positive, zirkulierende Monozyten und T-Zellen vor. In dieser Studie sollte der relative Beitrag freier und zellgebundener Komponenten zum Imaging von entzündeten Gelenken in der experimentellen Adjuvansarthritis (AA) analysiert werden. Methoden: Peritonealmakrophagen oder Lymphknoten- T-Zellen von AA-Ratten wurden in vitro mit Sättigungsmengen eines ^99mTc-Anti-CD4-mAk (W3/25) inkubiert und i.v. in Ratten mit AA (akute Phase; Tag 19) injiziert. Ergebnisse: Die In-vitro-Freisetzung des ^99mTcanti- CD4-mAk von den Zellen war begrenzt (im Durchschnitt 1,57%/h bei Makrophagen, 0,84%/h bei T-Zellen). Nach i.v. Injektion zeigten Ganzkörper-/Gelenkscans und Gewebemessungen eine zu vernachlässigende Akkumulation von Radioaktivität in den entzündeten Knöchelgelenken (Gewebe: 0,22 und 0,34% der injizierten Aktivität), während die Radioaktivität in der Leber (Gewebe: 79 und 71%), der Niere und der Harnblase konzentriert war. Im Gegensatz zu Makrophagen akkumulierten Anti-CD4-mAk-bedeckte T-Zellen signifikant in lymphoiden Organen, entzündeter Synovialmembran der Knöchelgelenke sowie Ellbogen- und Kniegelenken. Schlussfolgerung: Während der Gesamtbeitrag von zellgebundenen mAk zum Imaging arthritischer Gelenke mittels Anti-CD4-mAk minimal ist, weist eine differentielle Akkumulation von Makrophagen und T-Zellen in lymphoiden Organen und der entzündeten Synovialmembran auf präferentielle Wanderungsmuster dieser beiden Zellpopulationen in arthritischen Ratten hin. Obwohl in dieser Studie nur für ^99mTc-Anti-CD4-mAk validiert, können die Ergebnisse möglicherweise auf andere antizelluläre Antikörper mit vergleichbarer Affinität zu ihrem Antigen übertragen werden.

Keywords

Immunoscintigraphy - anti-CD4 mAb - macrophages - T-cells - adjuvant arthritis

Schlüsselwörter

Immunszintigraphie - Anti-CD4-Antikörper - Makrophagen - T-Zellen - Adjuvansarthritis

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