IVIg prevents post-ischemic leukocyte infiltration and maintains blood brain barrier integrity. (A) Administration of IVIg (2 g/kg) decreased leukocyte infiltration following 1 h and 23 h respectively of cerebral ischemia and reperfusion (I/R). **p < 0.01 compared to I/R mice, n = 8-12. (B) Representative flow cytometry plots showing the two studied populations of CD45+ cells, infiltrating leukocytes (CD45 high) and microglia (CD45 intermediate). (C) Treatment with high concentration of IVIg (5 mg/mL) reduced permeability of bEnd.3 cell monolayers subjected to oxygen and glucose deprivation (OGD). *p < 0.05 compared to OGD 3 h. (D, E and F) IVIg rescues the decrease in claudin 5 and occludin levels that occurs after 3 h OGD in untreated or vehicle controls. **p < 0.01. (G and H) A similar trend was seen in the expression levels of JAM-1 and ZO-1, however statistical significance was not reached. (I) Immunofluorescence staining showed the restoration of claudin 5 expression in IVIg-treated bEnd.3 cells subjected to 3 h OGD. Scale bar: 20 μm.