ICAM-1^null C57BL/6 Mice Are Not Protected from Experimental Ischemic Stroke

Accumulation of neutrophils in the brain is a hallmark of cerebral ischemia and considered central in exacerbating tissue injury. Intercellular adhesion molecule (ICAM)-1 is upregulated on brain endothelial cells after ischemic stroke and considered pivotal in neutrophil recruitment as ICAM-1-deficient mouse lines were found protected from experimental stroke. Translation of therapeutic inhibition of ICAM-1 into the clinic however failed. This prompted us to investigate stroke pathogenesis in Icam1^tm1Alb C57BL/6 mutants, a true ICAM-1^null mouse line. Performing transient middle cerebral artery occlusion, we found that absence of ICAM-1 did not ameliorate stroke pathology at acute time points after reperfusion. Near-infrared imaging showed comparable accumulation of neutrophils in the ischemic hemispheres of ICAM-1^null and wild type C57BL/6 mice. We also isolated equal numbers of neutrophils from the ischemic brains of ICAM-1^null and wild type C57BL/6 mice. Immunostaining of the brains showed neutrophils to equally accumulate in the leptomeninges and brain parenchymal vessels of ICAM-1^null and wild type C57BL/6 mice. In addition, the lesion size was comparable in ICAM-1^null and wild type mice. Our study demonstrates that absence of ICAM-1 neither inhibits cerebral ischemia-induced accumulation of neutrophils in the brain nor provides protection from ischemic stroke.