Preferential Recruitment of Monocyte into the Brain is Orchestrated by VCAM-1 Expression

The restriction of normal blood flow is the cause of many diseases including stroke and coronary artery diseases. To study the consequences of vessel blockade, previous models mainly focused on major arteries and have been well studied. However, the sequela from interruption of capillary vessels by microemboli was less well characterized. In this study, we exploited polystyrene microspheres as a mimicry of microemboli and found that microspheres of this size can be trapped in capillary vessels of all organs without causing apparent acute morbidities of the host. Interestingly, we accidentally found significantly increased recruitment of monocyte to the brain vasculature expressing low levels of Ly6C expression, but not to other organs. Further study revealed the spleen is the major origin of the recruited monocyte. Most importantly, VCAM-1 which is constitutively expressed on mouse brain vasculature orchestrates the recruitment of monocyte. Blockade of VCAM-1 in mice can substantially reduce monocyte recruitment. Interestingly, monocytes get activated through TNF- signaling which likely happens in the spleen instead of the brain. Collectively, we found a unique monocyte recruitment strategy in the brain comparing to other orangs, in response to capillary blockade induced by polystyrene microspheres.