MAC2 is a long‐lasting marker of peripheral cell infiltrates into the mouse CNS after bone marrow transplantation and coronavirus infection

Abstract

Microglia are the primary resident myeloid cells of the brain responsible for maintaining homeostasis and protecting the central nervous system (CNS) from damage and infection. Monocytes and monocyte-derived macrophages arising from the periphery have also been implicated in CNS pathologies, however, distinguishing between different myeloid cell populations in the CNS has been difficult. Here, we set out to develop a reliable histological marker that can assess distinct myeloid cell heterogeneity and functional contributions, particularly in the context of disease and/or neuroinflammation. scRNAseq from brains of mice infected with the neurotropic JHM strain of the mouse hepatitis virus (JHMV), a mouse coronavirus, revealed that Lgals3 is highly upregulated in monocyte and macrophage populations, but not in microglia. Subsequent immunostaining for galectin-3 (encoded by Lgals3), also referred to as MAC2, highlighted the high expression levels of MAC2 protein in infiltrating myeloid cells in JHMV-infected and bone marrow (BM) chimeric mice, in stark contrast to microglia, which expressed little to no staining in these models. Expression of MAC2 was found even 6-10 months following BM-derived cell infiltration into the CNS. We also demonstrate that MAC2 is not a specific label for plaqueassociated microglia in the 5xFAD mouse model, but only appears in a distinct subset of these cells in the presence of JHMV infection or during aging. Our data suggest that MAC2 can serve as a reliable and long-lasting histological marker for monocyte/ macrophages in the brain, identifying an accessible approach to distinguishing resident microglia from infiltrating cells in the CNS under certain conditions.

Aβ plaques do not protect against HSV‐1 infection in a mouse model of familial Alzheimer's disease, and HSV‐1 does not induce Aβ pathology in a model of late onset Alzheimer's disease

“…Both microglia and infiltrating myeloid cells exhibit phagocytic activities, and because the latter were shown to express microglia‐specific markers upon differentiation in brain parenchyma, defining the cell type responsible for phagocytic uptake of infected neurons has been difficult [ 74 ]. The current work supports the results of recent studies that Gal3 is a specific marker of infiltrating monocytes [ 49 ]. Moreover, our work revealed that a large fraction of infiltrating myeloid cells remained Iba1 negative at least within the first few days of residing in brain parenchyma.…”

“…To confirm these results, brains of hAβ mice challenged IC with McKrae were examined using immunostaining for Galectin 3 (Gal3, also known as MAC2 or LGALS3). Gal3 was recently shown to be a specific, long‐lasting marker of infiltrating myeloid cells [ 49 ]. Coimmunostaining using anti‐Gal3 and a‐HSV1 antibodies revealed massive infiltration by Gal3‐positive cells into brain areas affected by the virus (Figure 12A ).…”

Single cell RNA sequencing reveals immunomodulatory effects of stem cell factor and granulocyte colony-stimulating factor treatment in the brains of aged APP/PS1 mice

“…This finding suggests that SCF+G-CSF treatment may change the transcriptional profiles from one cell class to the other cell class. We found that the transcriptome in this cell cluster showed greater overlap with Mo/Mac reference datasets than with microglia datasets and included robust expression of the Mo/Mac marker Lgals3 [86]. Our findings also open the possibility that a subset of Mo/Mac that migrates to the brain following SCF+G-CSF treatment takes on a microglia transcriptional profile.…”

Polio Virotherapy of Malignant Glioma Engages the Tumor Myeloid Infiltrate and Induces Diffuse Microglia Activation

“…the syndromes modeled in mice infected with rhabdovirus (vesicular stomatitis virus) [13], flaviviruses (eg. West Nile virus) [42], or the neurotropic coronavirus, JHM mouse hepatitis virus [26], share common features implicated in triggering microglia activation [14]. They each infect neurons and inflict substantial neuronal damage; they each target astro- and/or oligodendrocytes for infection and cytopathogenic damage; they induce peripheral monocytic infiltration in the CNS.…”