Immune surveillance of the human central nervous system (CNS): Different migration pathways of immune cells through theblood–brain barrier and blood–cerebrospinal fluid barrier in healthy persons

Abstract

Since for immune surveillance, only lymphocytes in the activated state are able to enter normal human central nervous system (CNS), available data are briefly reviewed to reveal lymphocyte transfer through blood-brain barrier (bbb) and blood-cerebrospinal fluid barrier (bCSFb). With immuno-histochemical and -cytochemical methods, bbb was studied on brain microvessels and bCSFb on choroid plexus epithelium and microvessels. Lymphocyte transfer capacity on the barriers was determined with blood/CSF cell ratios revealed by quantified multicolour flow-cytometry of CSF and blood sample pairs. Four paths attenuated the restricted transfer of lymphocyte and NK cell subsets (none for B cells) through bbb and bCSFb, preferring memory cells in normal human brain, using different cell adhesion molecules (CAM). CAM pattern changed in choroid plexus where indication of lymphocyte recirculating from CSF into blood may exist in animal brains. Since efficiency of migration of blood-borne lymphocytes into CSF across bbb or bCSFb of normal human brain is not fully revealed, further data are needed to understand the transfer of immune cells across the barriers in health and disease.