Limb Regeneration: Ultrastructural and Cytological Aspects

Abstract

As previously indicated (Sect. 1.8), the injury of a limb in lizards induces large tissue damage that elicits a strong inflammatory reaction. Within 2–3 days after amputation, the reactive process is similar in the stump of the tail and the limb, and numerous granulocytes are present as the main phagocytes and persist in the following week (Alibardi 2009a), when also macrophages of blood origin become numerous. The latter phagocytes complete the tissue debridement but can cause scarring when they are hyperstimulated, for instance, by cauterization or repetitive cutting of the blastema (Alibardi 2009b). Macrophages are more commonly seen than granulocytes after 3 weeks after amputation.

The persistence of leukocytes in the injured limb together with the extensive exudation of fibrin that traps the microorganisms is a potent primitive innate immune defense of reptilian wounds (Huchezermayer and Cooper 2000). The permanence of active granulocytes for 1 week in the wounded tail and for over 3 weeks in wounded limbs indicates that these cells continue to be stimulated probably by a persistence of microbes and unknown chemical factors derived from tissue destruction (especially in the limb stump). In the injured tissues of the limb at 30–40 days after amputation, granulocytes within wounded tissues show an increased irregular surface and blebbing and contain activated (spongy-like) azurophil granules. These granules may store potent antimicrobial molecules that block the spreading of infection of injured lizard tissues of the stump.