Wound repair in the Amphioxus (Branchiostoma platae), an animal deprived of inflammatory phagocytes.

The existence of phagocytes in the Amphioxus is a matter of debate since early studies of Metchnikoff, who could not induce inflammation in this animal. To reinvestigate this important phenomenon, we sectioned the distal portion of the animal and analyzed, by morphological methods, the presence of phagocytes in the wound. The analysis of the wound by optical and electron microscopy did not detect cells with morphological characteristics of phagocytes in it. The wound is completely covered by the external cuticle of the animal 24 hr after the lesion was made. A second section of the animal leads to abnormal healing of the lesion. The insertion of a surgical silk thread in the muscle of the animals results--after 13 days--in a collection of cells surrounding the foreign body. The ultrastructural analysis of these cells showed they are endothelial cells rather than specialized phagocytes. Yet, the Amphioxus is able to mount an allograph rejection when the animals are tied together by suture. This intriguing capacity of the Amphioxus to cope with tissue healing, infection, and other pathologies without phagocytes is discussed.