Heat Shock Protein-27 Delays Acute Rejection After Cardiac Transplantation: An Experimental Model

BACKGROUND: Rejection is the major obstacle to survival after cardiac transplantation. We investigated whether overexpression of heat shock protein (Hsp)-27 in mouse hearts protects against acute rejection and the mechanisms of such protection. METHODS: Hearts from B10.A mice overexpressing human Hsp-27 (Hsp-27tg), or Hsp-27–negative hearts from littermate controls (LCs) were transplanted into allogeneic C57BL/6 mice. The immune response to B10.A hearts was investigated using quantitative polymerase chain reaction for CD3+, CD4+, CD8+ T cells, and CD14+ monocytes and cytokines (interferon-γ, interleukin [IL]-2, tumor necrosis factor-α, IL-1β, IL-4, IL-5, IL-10, transforming growth factor-β) in allografts at days 2, 5, and 12 after transplantation. The effect of Hsp-27 on ischemia-induced caspase activation and immune activation was investigated. RESULTS: Survival of Hsp-27tg hearts (35±10.37 days, n=10) was significantly prolonged compared with LCs (13.6±3.06 days, n=10, P=0.0004). Hsp-27tg hearts expressed significantly more messenger RNA (mRNA) markers of CD14+ monocytes at day 2 and less mRNA markers of CD3+ and CD8+T cells at day 5 compared with LCs. There was more IL-4 mRNA in Hsp-27tg hearts at day 2 and less interferon-γ mRNA at day 5 compared with LCs. Heat shock protein-27tg hearts subjected to ischemia or to 24 hr ischemia-reperfusion injury demonstrated significantly less apoptosis and activation of caspases 3, 9, and 1 than LCs. T cells removed from C57BL/6 recipients of Hsp-27tg hearts produced a vigorous memory response to B10.A antigens, suggesting immune activation was not inhibited by Hsp-27. CONCLUSION: Heat shock protein-27 delays allograft rejection, by inhibiting tissue damage, through probably an antiapoptotic pathway. It may also promote an anti-inflammatory subset of monocytes.