Histological and Immunohistochemical Evaluation of Autologous Cultured Bone Marrow Mesenchymal Stem Cells and Bone Marrow Mononucleated Cells in Collagenase-Induced Tendinitis of Equine Superficial Digital Flexor Tendon
(T21) Tissue slides from the superficial digital flexor tendons (SDFT) following experimentally induced tissue injury and subsequent treatment with Fibrin (), Saline (d), and normal tendon (e). Tissue stains with hematoxylin-eosin (H and E) and Herovyci (Hero) show loss of the longitudinal fiber pattern and crimp in tendons treated with-Fibrin (); in Saline treated tendon (d), there is complete disruption with randomly oriented fibers, clearly shown in the central area. The collagen I/III ratio in Fibrin treated tendon (c) is clearly lower than in normal (e) and cell grafted tendon (Figures 3(a) and 3(b)); in Saline (d) treated tendon, the central zone was highly positive for collagen type III but not for type I. Stains for cartilage oligomeric matrix protein (COMP) show stack and spread expression in both control-treated SDFT (c-d). In immunohistochemistry staining for the expression of CD34+ mononucleated cells in Fibrin (), Saline (d) and Normal (e) Tendon, only sporadic CD34+ stained mononuclear elements were detected. By contrast, in all three placebo-treated SDFTs, the location of the lesion was readily identified as an area with high positivity for type III collagen, very low expression of type I collagen and in some zones, evidence of mineralization. Similarly to the trend of type I collagen expression, COMP was expressed in a homogeneous and diffuse pattern in sham untreated control SDFTs as well as in cBMSC- and BMMNCS-injected tendons. Scant, weak expression of COMP, restricted to areas that circumscribed the injected portions of the tendon, was observed in all three placebo-treated SDFTs. As expected, no CD34+ mononuclear cells were observed in the sham tendon sections. Similar results were obtained in sections of placebo-injected SDFTs, although a certain number of inflammatory cells were present, interspersed in perivascular areas of these tendons (data not shown). Only sporadic CD34+ stained mononuclear elements (i.e., 0 to 2 per HPF) were observed in cBMSC-injected tendons (data not shown). On the contrary, in BMMNCS-treated SDFTs large numbers of mononucleated cells, in part CD34+ stained, were present in the interfascicular zone.
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