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. 2015 Jan 1;4(1):39–53. doi: 10.1089/biores.2014.0055

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© Daniela Zwolanek et al. 2015; Published by Mary Ann Liebert, Inc.

This Open Access article is distributed under the terms of the Creative Commons License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.

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FIG. 5. — Expression of α2 integrin at MSC attachment sites to bone and cartilage. (A) Expression of collagen I and collagen II in cryosections of intact osteochondral explants. Immunofluorescence analysis was performed on cryosections of hPLAP prestained intact osteochondral explants by incubation with polyclonal antibodies against collagen I and collagen II. Collagen I is found in bone tissue, whereas collagen II is exclusively located in cartilage tissue of the intact explant. (B) Alcian blue-PAS staining of intact osteochondral explants and explants with a full-thickness defect. Articular cartilage is stained purple, subchondral bone is stained magenta, and proteoglycans are stained blue. (C, D) Expression of α2 integrin in osteochondral explants with full-thickness defects. Co-immunofluorescence analysis was performed on cryosections of previously hPLAP-stained and quantified osteochondral explants by parallel incubation with an antibody against α2 integrin (C, D, green), and a polyclonal antibody against collagen I (C, red) and collagen II (D, red). α2 integrin and collagen I and II are co-expressed in distinct adjacent zones (merge, yellow, arrows). Merging with bright light (bl) images demonstrated the co-expression of α2 integrin and collagen I at sites where hPLAP-tg MSC attach to subchondral bone (C, bl merged, arrows). Bright light-merged images after co-staining of α2 integrin and collagen II revealed co-expressing sites where hPLAP-tg MSC attach to collagen II (D, bl merged, arrows). (E, F) Expression of α1 and α5 integrin in osteochondral explants with full-thickness defects. Immunofluorescence analysis was performed on hPLAP-prestained cryosections of osteochondral explants by incubation with a monoclonal antibody against α1 integrin (E) and a polyclonal anti-α5 integrin antibody (F). Expression of neither α1 nor α5 integrin could be observed at sites where hPLAP-tg MSC attach to the cartilage lesion (bl merged, arrows). Scale bar=50 μm.