B7-H3 upregulation in ischemic stroke: friend or foe?

B7-H3 (CD276) is an immune checkpoint co-signaling molecule expressed on immune and non-immune cells. It is best known for suppressing T-cell responses but can also promote inflammation depending on the microenvironment. In neuroinflammatory models such as experimental autoimmune encephalomyelitis, B7-H3 expression increases concomitantly with the inflammatory response, and its inhibition is associated with reduced disease progression. Although its role in ischemic stroke remains unclear, we hypothesized that cerebral ischemia/reperfusion (I/R) would upregulate B7-H3 expression in the ischemic brain and that increased B7-H3 expression would positively correlate with pro-inflammatory cytokine expression. Young and aged male and female rodents, including normotensive and spontaneously hypertensive rats to model comorbid hypertension, underwent transient middle cerebral artery occlusion (MCAO) followed by reperfusion. Brain tissue was collected on post-MCAO days 1, 3, 5, or 7. B7-H3 mRNA was analyzed by real-time PCR, whereas protein expression was assessed by Western blotting and immunohistochemistry at selected time points. B7-H3 expression was significantly upregulated in the ischemic brain across sexes, age groups, and species. The extent of B7-H3 degradation was influenced by species, sex, age, and time after cerebral I/R. Upregulation of B7-H3 was observed at both the mRNA and protein levels and was localized primarily to the somatosensory cortex and caudate putamen in the ipsilateral (ischemic) hemisphere, the main regions affected in this MCAO model. Elevated B7-H3 expression in the ischemic brain positively correlated with the pro-inflammatory mediator TNFα. In rats, the temporal profile of B7-H3 expression paralleled the early inflammatory phase associated with secondary tissue damage after ischemic stroke. These findings identify B7-H3 as an ischemia-induced immune checkpoint molecule in the brain that may modulate post-stroke immune responses and support further investigation into its beneficial versus detrimental roles in neuroinflammation and its potential as a therapeutic target following cerebral I/R.