Lymphatic Drainage of Cerebrospinal Fluid Using Lymph Node Seeker 64Cu‐Labeled Gram‐Negative Bacterial Extracellular Vesicles With Positron Emission Tomography (PET)

ABSTRACT Cerebrospinal fluid (CSF) is drained into the systemic lymphatics via paravertebral lymph nodes. Superficial and deep cervical lymph nodes collect CSF in mice, but the exact and quantified routes are unknown. Recently, we simultaneously visualized cervical, sacral and iliac lymph nodes via serial imaging on the intrathecal [ 64 Cu]Cu‐albumin positron emission tomography. Paravertebral lymph nodes might act as sentinels to monitor the CSF, brain, and spinal cord. We used 64 Cu‐labeled Escherichia coli extracellular vesicles, outer membrane vesicles (OMVs), as lymph node seekers for intrathecal administration and quantified the differential amounts of various paravertebral lymph nodes along the axis of the brain and spinal cord in mice. The quantified results revealed 77.3% in superficial and deep cervical lymph nodes, 11.4% in abdominal/pelvic lymph nodes and 11.3% in sacral lymph nodes. Click‐labeled [ 64 Cu]Cu‐OMVs were drained to reach and stop at the lymph nodes on serial quantification. The cervical lymph nodes drained most of the OMV‐laden CSF, which is proportional to the surface areas of the brain (70%) and spinal cord in mice. We propose that all paravertebral lymph nodes monitor the segmental regions of the brain and spinal cord as immediate sentinel lymph nodes against the central nervous system.