Lack of interleukin-1 receptor antagonist modulates plaque composition in apolipoprotein E-deficient mice

Objective - Interleukin (IL)-1 plays an important role in atherosclerosis. IL-1 receptor antagonist (IL-1Ra) is an endogenous inhibitor of IL-1. However, the role of IL-1Ra in the development of atherosclerosis is poorly understood. Methods and Results - Mice that lacked IL-1Ra (IL-1Ra-/-) were crossed with apolipoprotein E-deficient (E-/-) mice and formation of atherosclerotic lesions was analyzed after 16 weeks or 32 weeks consumption of a normal chow diet. This study focused on the comparison of atherosclerotic lesion between IL-1Ra+/+/apoE-/- (n = 12) and IL-1Ra(+/-)/apoE-/- mice (n = 12), because of the significantly leaner phenotype in IL-1Ra-/-/apoE-/- mice compared with the others. Interestingly, atherosclerotic lesion size in IL-1Ra+/-/apoE-/- mice at age 16 weeks was significantly increased (30%) compared with IL-1Ra+/+/apoE-/- mice (P < 0.05). At 32 weeks, the differences of lesion size between these mice failed to achieve statistical significance. However, immunostaining demonstrated an 86% (P < 0.0001) increase in the MOMA-2- stained lesion area of IL-1Ra+/-/apoE-/- mice. In addition, alpha-actin staining in these lesions was significantly decreased (-15%) compared with those in IL-1Ra+/+/apoE-/- mice (P < 0.05). Conclusions - These results suggest an important role of IL-1Ra in the suppression of lesion development during early atherogenesis and furthermore indicate its role in the modulation of plaque composition.