Demineralised freeze-dried bone allograft (DFDBA) is regarded as OSTEOINDUCTIVE because it contains growth factors. Which of the following is NOT one of them?

Correct answer: A. Interleukin-1

• A. CORRECT — this is the exception. INTERLEUKIN-1 is a pro-inflammatory CYTOKINE. Far from inducing bone formation, IL-1 is one of the principal mediators of bone RESORPTION in periodontitis: it upregulates RANKL, stimulates osteoclastogenesis and drives matrix metalloproteinase production. IL-1 gene polymorphisms are studied as a periodontal risk marker. It is not an osteoinductive growth factor and it is not the reason DFDBA works.
• B. TGF-beta is abundant in bone matrix and stimulates osteoblast proliferation and matrix synthesis.
• C. BONE MORPHOGENETIC PROTEINS are the essential osteoinductive component. Demineralisation of the allograft with hydrochloric acid removes the mineral phase and EXPOSES the BMPs bound within the bone matrix, allowing them to induce undifferentiated mesenchymal cells to differentiate into osteoblasts. This is exactly why DFDBA is osteoinductive while non-demineralised FDBA is only osteoconductive.
• D. PDGF is present in bone matrix and is a potent mitogen and chemoattractant for osteoblasts and periodontal ligament cells; recombinant PDGF is itself used clinically in periodontal regeneration.

Note: Distinguish the three graft mechanisms cleanly. OSTEOGENIC — the graft contains living bone-forming cells; only AUTOGRAFT qualifies. OSTEOINDUCTIVE — the graft induces host cells to become osteoblasts, via BMPs; DFDBA. OSTEOCONDUCTIVE — the graft is a passive scaffold for ingrowth; FDBA, xenograft, alloplast.