The influence of macrophage depletion on ligament healing

Connect Tissue Res. 2011 Jun;52(3):203-11. doi: 10.3109/03008207.2010.511355. Epub 2010 Nov 30.

Abstract

Despite a complex cascade of cellular events to reconstruct damaged extracellular matrix (ECM), ligament healing results in a mechanically inferior, scar-like tissue. During normal healing, the number of macrophages significantly increases within the wound site. Then, granulation tissue expands into any residual, normal ligamentous tissue (creeping substitution), resulting in a larger region of healing, greater mechanical compromise, and an inefficient repair process. To study the effects of macrophages on the repair process, bilateral, surgical rupture of their medial collateral ligaments (MCLs) was done on rats. Treatment animals received liposome-encapsulated clodronate, 2 days before rupture to ablate phagocytosing macrophages. Ligaments were then collected at days 5, 11, and 28 for immunohistochemistry (IHC) and/or mechanical testing. Clodronate treatment reduced both the M1 and M2 macrophages at day 5 and altered early healing. However, the macrophages effectively returned to control levels after day 5 and reinitiated a wound-healing response. Our results suggest that an early macrophage response, which is necessary for debridement of damaged tissue in the wound, is also important for cytokine release to mediate normal repair processes. Additionally, nonspecific inhibition of macrophages (without regard to specific macrophage populations) can control excessive granulation tissue formation but is detrimental to early matrix formation and ligament strength.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Biomechanical Phenomena / drug effects
  • Cell Movement / drug effects
  • Clodronic Acid / pharmacology
  • Collagen / biosynthesis
  • Endothelial Cells / drug effects
  • Endothelial Cells / pathology
  • Granulation Tissue / drug effects
  • Granulation Tissue / pathology
  • Immunohistochemistry
  • Liposomes / chemistry
  • Macrophages / drug effects
  • Macrophages / pathology*
  • Male
  • Medial Collateral Ligament, Knee / pathology*
  • Myofibroblasts / drug effects
  • Myofibroblasts / pathology
  • Rats
  • Rats, Wistar
  • T-Lymphocytes / cytology
  • T-Lymphocytes / drug effects
  • Wound Healing* / drug effects

Substances

  • Liposomes
  • Clodronic Acid
  • Collagen