It is now increasingly clear that human stroke can have other serious consequences besides brain damage that can impact on patient survival and recovery. For example, many stroke patients succumb to CNS injury-induced immunodepression and fatal infections. Our prior work suggests that evolving cerebral ischemic injury elicits a cycle of injury from brain-to-spleen-to-brain that is strongly influenced by sex. We determined if splenic immunocytes are important in contributing to sex differences in post-ischemic brain injury. Male and female C57BL/6J mice were splenectomized 14 days before experimental stroke. Male and female mice with or without splenectomy (n=9-10 per group) then underwent 60 min of middle cerebral artery occlusion (MCAO) via intraluminal filament. Laser-Doppler flowmetry (LDF) was used to monitor cortical perfusion. All mice were euthanized and brains collected at 96 hours of reperfusion. Infarct volume (% corrected contralateral structure) was determined by image analysis of coronal brain slices stained with 2,3,5-triphenyltetrazolium chloride. Mean arterial blood pressure (MABP), blood gases (pH, P
a
O
2
, P
a
CO
2
), and blood glucose were measured at 30 min MCAO and at 15 min of reperfusion in separate groups of male and female mice with or without splenectomy (n=5 per group). Relative LDF changes (% baseline), MABP, blood gases, and blood glucose during and after MCAO were comparable among the experimental groups. We observed that infarct volume in females (cortex, 41±4%; striatum, 55±6%) was smaller (
P
<0.05) compared to males (cortex, 52±3%; striatum, 75±3%) at 96 hours of reperfusion. However, no differences (cortex,
P
=0.313; striatum,
P
=0.601) in infarct volume were seen between splenectomized male (cortex, 43±4%; striatum, 51±7%) and female (cortex, 38±4%; striatum, 46±5%) mice. Our data suggest that removal of all splenocyte lineages via splenectomy attenuates sex differences in post-ischemic brain injury. Future studies will evaluate the role of different splenic immunocyte subsets, such as T or B lymphocytes, on male vs. female ischemic brain outcomes. This study was supported by National Institutes of Health grant NS076013.
Male and Female Mice Exhibit Divergent Responses of the Cortical Vasculature to Traumatic Brain Injury