title: SPECT imaging of joint inflammation with Nanobodies targeting the macrophage mannose receptor in a mouse model for rheumatoid arthritis.
abstract: Rheumatoid arthritis (RA) is a chronic autoimmune disease occurring in approximately 1% of the worldwide population. The disease primarily affects the joints, where inflammatory cells, such as macrophages, invade the synovium and cause cartilage and bone destruction. Currently, it is difficult to efficiently diagnose and monitor early-stage RA. In this study, we investigated whether SPECT/micro-CT imaging with (99m)Tc-labeled Nanobodies directed against the macrophage mannose receptor (MMR) is a useful tool for monitoring and quantifying joint inflammation in collagen-induced arthritis (CIA), a mouse model for RA. The expression of MMR was analyzed on macrophages and osteoclasts generated in vitro and in cells obtained from various organs from mice with CIA.
  
  
  METHODS
  CIA was induced in DBA/1 mice by injection of collagen type II in complete Freund adjuvant, and cell suspensions from the inflamed joints and other organs were obtained. Macrophages and osteoclasts were generated in vitro from bone marrow cells. Expression of MMR was quantified by quantitative polymerase chain reaction and flow cytometry with specific Nanobodies and conventional antibodies. SPECT/micro-CT imaging was performed with (99m)Tc-labeled MMR and control Nanobodies.
  
  
  RESULTS
  MMR was highly expressed on macrophages and to a lesser extent on osteoclasts generated in vitro. In mice with CIA, MMR expression was detected on cells from the bone marrow, lymph nodes, and spleen. In synovial fluid of arthritic joints, MMR was expressed on CD11b(+)F4/80(+) macrophages. On in vivo SPECT/micro-CT imaging with consecutive injections of MMR and control Nanobodies, a strong MMR signal was seen in the knees, ankles, and toes of arthritic mice. Quantification of the SPECT imaging confirmed the specificity of the MMR signal in inflamed joints as compared with the control Nanobody. Dissection of the paws revealed an additional significant MMR signal in nonarthritic paws of affected mice (i.e., mice displaying symptoms of arthritis in other paws).
  
  
  CONCLUSIONS
  Our data show that MMR is expressed on macrophages in vitro and in vivo in synovial fluid of inflamed paws, whereas expression is relatively low in other tissues. The use of Nanobodies against MMR in SPECT/micro-CT imaging generates the possibility to track inflammatory cells in vivo in arthritic joints.
authors: Laboratory of Immunobiology, Rega Institute, Katholieke Universiteit Leuven, Leuven, Belgium.
authors: Stéphanie
authors: S
authors: Put
authors: Steve
authors: S
authors: Schoonooghe
authors: Nick
authors: N
authors: Devoogdt
authors: Evelien
authors: E
authors: Schurgers
authors: Anneleen
authors: A
authors: Avau
authors: Tania
authors: T
authors: Mitera
authors: Matthias
authors: M
authors: D'Huyvetter
authors: Patrick
authors: P
authors: De Baetselier
authors: Geert
authors: G
authors: Raes
authors: Tony
authors: T
authors: Lahoutte
authors: Patrick
authors: P
authors: Matthys
mesh_terms: D000818:Animals; D001172:Arthritis, Rheumatoid / Q000000981:diagnostic imaging* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D004195:Disease Models, Animal; D005786:Gene Expression Regulation; D007249:Inflammation / Q000000981:diagnostic imaging / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D037181:Lectins, C-Type / Q000235:genetics / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D015609:Organotechnetium Compounds; D010010:Osteoclasts / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D061905:Single-Domain Antibodies; D013583:Synovial Membrane / Q000378:metabolism / Q000473:pathology; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D037181:Lectins, C-Type; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D015609:Organotechnetium Compounds; D011956:Receptors, Cell Surface; D061905:Single-Domain Antibodies
keywords: Nanobody; collagen-induced arthritis (CIA); macrophage mannose receptor (MMR); single photon emission computed tomography (SPECT)