Microglial nodules in early multiple sclerosis white matter are associated with degenerating axons

Morphometric characterization of microglial phenotypes in human cerebral cortex

Background

Microglia can adopt different morphologies, ranging from a highly ramified to an amoeboid-like phenotype. Although morphological properties of microglia have been described in rodents, little is known about their fine features in humans. The aim of this study was to characterize the morphometric properties of human microglia in gray and white matter of dorsal anterior cingulate cortex (dACC), a region implicated in behavioral adaptation to neuroinflammation. These properties were compared to those of murine microglia in order to gain a better appreciation of the differences displayed by these cells across species.

Methods

Postmortem dACC samples were analyzed from 11 individuals having died suddenly without any history of neuroinflammatory, neurodegenerative, nor psychiatric illness. Tissues were sectioned and immunostained for the macrophage marker Ionized calcium binding adaptor molecule 1 (IBA1). Randomly selected IBA1-immunoreactive (IBA1-IR) cells displaying features corresponding to commonly accepted microglial phenotypes (ramified, primed, reactive, amoeboid) were reconstructed in 3D and all aspects of their morphologies quantified using the Neurolucida software. The relative abundance of each morphological phenotype was also assessed. Furthermore, adult mouse brains were similarly immunostained, and IBA1-IR cells in cingulate cortex were compared to those scrutinized in human dACC.

Results

In human cortical gray and white matter, all microglial phenotypes were observed in significant proportions. Compared to ramified, primed microglia presented an average 2.5 fold increase in cell body size, with almost no differences in branching patterns. When compared to the primed microglia, which projected an average of six primary processes, the reactive and amoeboid phenotypes displayed fewer processes and branching points, or no processes at all. In contrast, the majority of microglial cells in adult mouse cortex were highly ramified. This was also the case following a postmortem interval of 43 hours. Interestingly, the morphology of ramified microglia was strikingly similar between species.

Conclusions

This study provides fundamental information on the morphological features of microglia in the normal adult human cerebral cortex. These morphometric data will be useful for future studies of microglial morphology in various illnesses. Furthermore, this first direct comparison of human and mouse microglia reveals that these brain cells are morphologically similar across species, suggesting highly conserved functions.

Immunomodulatory function of κ-carrageenan oligosaccharides acting on LPS-activated microglial cells

The major neurodegenerative diseases are characterized by increasing of activated-microglial cells and inflammatory cytokines in the central nervous system. Carrageenan extracted from red algae is a kind of polysaccharide with sulfate groups. The oligosaccharides were obtained from carrageenan by enzymatic degradation. To detect the immunomodulatory activity of κ-carrageenan oligosaccharides (KOS) on microglial cells and the relationship to the sulfate group content, the desulfated derivatives of KOS (DSK) were obtained by dimethyl sulfoxide-methanol-pyridine method. KOS was labeled with fluorescein isothiocyanate. The effect of KOS and DSK on lipopolysaccharide (LPS)-activated microglial cells was detected. Hematoxylin-eosin staining and flow cytometric were used to detect the cell viability. The "scratch" migration assay, ornithine analysis and RT-PCR were used to determine the cell migration, arginase and TNF-α released by microglial cells, respectively. The effect of LPS and KOS on microglial cells was determined by flow cytometry and laser scanning confocal microscopy. The results showed that KOS and DSK could inhibit the cell viability, arginase and TNF-α released by LPS-activated microglia cell with concentration dependent manner. But the effect of DSK was weaker than that of KOS. KOS aggregated on the cell surface firstly, and then they enter into the cell to the nucleus, spread over the entire cell finally. But the exist of LPS could prevent the entrance of KOS. It could be concluded that KOS could protect microglial cells from being activated by LPS, and its inhibition function had relationship to the sulfate group content of KOS, while there were competition between LPS and KOS.

Role of microglia in CNS autoimmunity

Multiple sclerosis (MS) is the most common autoimmune disease of the central nervous system (CNS) in the Western world. The disease is characterized histologically by the infiltration of encephalitogenic T_H1/T_H17-polarized CD4⁺ T cells, B cells, and a plethora of myeloid cells, resulting in severe demyelination ultimately leading to a degeneration of neuronal structures. These pathological processes are substantially modulated by microglia, the resident immune competent cells of the CNS. In this overview, we summarize the current knowledge regarding the highly diverse and complex function of microglia during CNS autoimmunity in either promoting tissue injury or tissue repair. Hence, understanding microglia involvement in MS offers new exciting paths for therapeutic intervention.