Density of TMEM119-positive microglial cells in postmortem cerebrospinal fluid as a surrogate marker for assessing complex neuropathological processes in the CNS

Routine coronal paraffin-sections through the dorsal frontal and parieto-occipital cortex of a total of sixty cases with divergent causes of death were immunohistochemically (IHC) stained with an antibody against TMEM119. Samples of cerebrospinal fluid (CSF) of the same cases were collected by suboccipital needle-puncture, subjected to centrifugation and processed as cytospin preparations stained with TMEM119. Both, cytospin preparations and sections were subjected to computer-assisted density measurements. The density of microglial TMEM119-positive cortical profiles correlated with that of cytospin results and with the density of TMEM119-positive microglial profiles in the medullary layer. There was no statistically significant correlation between the density of medullary TMEM119-positive profiles and the cytospin data. Cortical microglial cells were primarily encountered in supragranular layers I, II, and IIIa and in infragranular layers V and VI, the region of U-fibers and in circumscribed foci or spread in a diffuse manner and high density over the white matter. We have evidence that cortical microglia directly migrate into CSF without using the glympathic pathway. Microglia in the medullary layer shows a strong affinity to the adventitia of deep vessels in the myelin layer. Selected rapidly fatal cases including myocardial infarcts and drowning let us conclude that microglia in cortex and myelin layer can react rapidly and its reaction and migration is subject to pre-existing external and internal factors. Cytospin preparations proved to be a simple tool to analyze and assess complex changes in the CNS after rapid fatal damage. There is no statistically significant correlation between cytospin and postmortem interval. Therefore, the quantitative analyses of postmortem cytospins obviously reflect the neuropathology of the complete central nervous system. Cytospins provide forensic pathologists a rather simple and easy to perform method for the global assessment of CNS affliction.