Immunolocalization of 5BrdU long retaining labeled cells and macrophage infiltration in the scarring limb of lizard after limb amputation

• Lizard limb regeneration brings to scarring.
• Intense inflammatory reaction occurs.
• Macrophage invasion as indicated by immunocytochemistry.
• Early differentiation of the wound epidermis.
• Lack of an apical epidermal peg favoring limb regeneration.

After limb amputation in lizards no regeneration occurs following massive inflammatory reaction. Light immunocytochemistry for CD68 and ultrastructural observations show that numerous macrophages persist for over 18 days post-amputation in the limb and fibroblasts producing high levels of collagen are present underneath a differentiating wound epidermis. Injections of 5BrdU for 1 week in normal lizards followed by a 4 weeks chase period indicate that most Long Retention Cells are present in the dense connectives of the dermis and inter-muscle septa, sparse cells in bone marrow and epidermis and scattered cells in muscle satellite cells. Most of the fibrocytes forming the scarring outgrowth of the amputated limb likely derive from the proliferation of dermal and inter-muscle fibrocytes after amputation. Differently from the tail where autotomous planes limit the extension of the damage, in the limb the injury produces massive tissue damage that favors intense and lasting inflammation. Numerous CD68 labeled macrophages likely stimulate fibroblast activation and rapid production of collagen fibrils underneath the wound epidermis. The latter does not form a growing apical region but rapidly differentiates into a mature epidermis so that no distal elongation of the limb occurs and a scar is instead formed.