Preconditioned or IL4-Secreting Mesenchymal Stem Cells Enhanced Osteogenesis at Different Stages.

Pathogen-associated molecular patterns, damage-associated molecular patterns, and other noxious stimuli activate macrophages to induce the proinflammatory responses. Modulation of inflammatory macrophages (M1) into an anti-inflammatory tissue repair macrophage (M2) phenotype at the appropriate time optimizes bone remodeling and regeneration. Simulating the proinflammatory stimuli by using preconditioned mesenchymal stem cells (MSCs) at an earlier stage, and alleviate the inflammation by using IL4-secreting MSCs at a later stage could further optimize bone regeneration in chronic inflammatory conditions, including periprosthetic osteolysis.