Abstract
Although IL-6 mRNA expression in rat is restricted to the first day post-fracture, the inflammatory phase, the protein has been observed later in the healing process, indicating additional roles. The importance of IL-6 was demonstrated by delayed healing in knockout mice through diminished osteoclast numbers, formation thereof being stimulated by IL-6. The aim of our study was to investigate with which cells this cytokine is associated and when during fracture healing.
A closed fracture of the lower right limb was created in rats. The tibia was obtained from six animals at each of 1, 3, 7, 14 and 28 days post-fracture, decalcified and prepared for standard immunohistochemistry with an IL-6-specific polyclonal antibody. The number and types of cells positively stained for IL-6 along the whole length of the periosteal callus on one surface and in the fracture was evaluated.
Mostly inflammatory cells were initially stained, becoming virtually absent by day 7 when this phase has normally ended. Within the immediate vicinity of the fracture where endochondrial ossification occurred, staining of chondrocytes was significant (69%) by day 7 when this cell was laying down cartilaginous tissue that was also calcified. Distally to the fracture where direct bone formation occurred through intra-membranous ossification by osteoblasts, staining of these cells was observed, peaking at day 14 (56%). As this bone started to take on the appearance of cortex and surviving embedded osteoblasts differentiated to osteocytes, the latter cells were stained, suggesting a role in remodelling. At the fracture as bone replaced the cartilaginous tissue and union occurred, staining of chondrocytes decreased, whereas local osteoblasts were positive.
IL-6 appears to play a role throughout fracture healing, in endochondrial and intra-membranous ossification. The level of staining of each cell type reflected the degree of their activity with respect to production of related tissue.
Correspondence should be addressed to EORS Secretariat Mag. Gerlinde M. Jahn, c/o Vienna Medical Academy, Alserstrasse 4, 1090 Vienna, Austria. Fax: +43-1-4078274. Email: eors@medacad.org
