Pax5 maintains cellular identity by repressing gene expression throughout B cell differentiation.

The transcription factor Pax5 is required for many aspects of B-lymphopoiesis including lineage commitment, immunoglobulin rearrangement, pre-BCR signalling and mature B cell survival. Pax5 regulates B cell lineage commitment by concurrently activating B cell specific gene expression as well as suppressing the expression of genes associated with non-B cell fates. The identity of the molecular targets of Pax5-mediated gene repression is the subject of much current interest. Recent studies have documented the essential nature of the Pax5 repression of the stem cell transcriptional program, as well as the silencing of lineage inappropriate gene expression, for B cell development. Surprisingly the repression of genes by Pax5 continues throughout lymphopoiesis, with the loss of Pax5 in mature B cell resulting in the reactivation of the same Pax5 targets during plasma cell differentiation. These recent insights into the mechanism of action of Pax5 in controlling B cell identity will be discussed

Microglia deficiency accelerates prion disease but does not enhance prion accumulation in the brain: Microglia and prion disease

Prion diseases are transmissible, neurodegenerative disorders associated with misfolding of the prion protein. Previous studies show that reduction of microglia accelerates central nervous system (CNS) prion disease and increases the accumulation of prions in the brain, suggesting that microglia provide neuroprotection by phagocytosing and destroying prions. In Csf1r (ΔFIRE) mice, the deletion of an enhancer within Csf1r specifically blocks microglia development, however, their brains develop normally and show none of the deficits reported in other microglia‐deficient models. Csf1r (ΔFIRE) mice were used as a refined model in which to study the impact of microglia‐deficiency on CNS prion disease. Although Csf1r (ΔFIRE) mice succumbed to CNS prion disease much earlier than wild‐type mice, the accumulation of prions in their brains was reduced. Instead, astrocytes displayed earlier, non‐polarized reactive activation with enhanced phagocytosis of neuronal contents and unfolded protein responses. Our data suggest that rather than simply phagocytosing and destroying prions, the microglia instead provide host‐protection during CNS prion disease and restrict the harmful activities of reactive astrocytes

Cell origin and niche availability dictate the capacity of peritoneal macrophages to colonize the cavity and omentum

The relationship between macrophages of the peritoneal cavity and the adjacent omentum remains poorly understood. Here, we describe two populations of omental macrophages distinguished by CD102 expression and use an adoptive cell transfer approach to investigate whether these arise from peritoneal macrophages, and whether this depends upon inflammatory status, the origin of peritoneal macrophages and availability of the omental niches. We show that whereas established resident peritoneal macrophages largely fail to migrate to the omentum, monocyte-derived resident cells readily migrate and form a substantial component of omental CD102(+) macrophages in the months following resolution of peritoneal inflammation. In contrast, both populations had the capacity to migrate to the omentum in the absence of endogenous peritoneal and omental macrophages. However, inflammatory macrophages expanded more effectively and more efficiently repopulated both CD102(+) and CD102(−) omental populations, whereas established resident macrophages partially reconstituted the omental niche via recruitment of monocytes. Hence, cell origin determines the migration of peritoneal macrophages to the omentum and predisposes established resident macrophages to drive infiltration of monocyte-derived cells

Cloning and expression of feline colony stimulating factor receptor (CSF-1R) and analysis of the species specificity of stimulation by colony stimulating factor-1 (CSF-1) and interleukin-34 (IL-34).

AbstractColony stimulating factor (CSF-1) and its receptor, CSF-1R, have been previously well studied in humans and rodents to dissect the role they play in development of cells of the mononuclear phagocyte system. A second ligand for the CSF-1R, IL-34 has been described in several species. In this study, we have cloned and expressed the feline CSF-1R and examined the responsiveness to CSF-1 and IL-34 from a range of species. The results indicate that pig and human CSF-1 and human IL-34 are equally effective in cats, where both mouse CSF-1 and IL-34 are significantly less active. Recombinant human CSF-1 can be used to generate populations of feline bone marrow and monocyte derived macrophages that can be used to further dissect macrophage-specific gene expression in this species, and to compare it to data derived from mouse, human and pig. These results set the scene for therapeutic use of CSF-1 and IL-34 in cats

Microglia promote anti-tumor immunity and suppress breast cancer brain metastasis

Breast cancer brain metastasis (BCBM) is a lethal disease with no effective treatments. Prior work has shown that brain cancers and metastases are densely infiltrated with anti-inflammatory, protumorigenic tumor associated macrophages (TAMs), but the role of brain resident microglia remains controversial because they are challenging to discriminate from other TAMs. Using single-cell RNA-sequencing (scRNA-seq), genetic, and humanized mouse models, we specifically identify microglia and find that they play a distinct pro-inflammatory and tumor suppressive role in BCBM. Animals lacking microglia show increased metastasis, decreased survival, and reduced NK and T cell responses, showing that microglia are critical to promote antitumor immunity to suppress BCBM. We find that the pro-inflammatory response is conserved in human microglia, and markers of their response are associated with better prognosis in BCBM patients. These findings establish an important role for microglia in anti-tumor immunity and highlight them as a potential immunotherapy target for brain metastasis

Analysis of the impact of Colony Stimulating Factor (CSF)-1 administration in adult rats using a novel Csf1r-mApple reporter gene

Macrophages are present in large numbers in every tissue in the body where they play critical roles in development and homeostasis. They exhibit remarkable phenotypic and functional diversity, underpinning their adaptation to specialized roles in each tissue niche. CSF1, signaling through the CSF1 receptor, which is restricted to monocyte-macrophage lineage cells in adults, is a critical growth factor controlling macrophage proliferation, differentiation, and many aspects of mature macrophage function. We have generated a macrophage reporter rat, utilizing a construct containing elements of the mouse Csf1r promoter and the highly conserved Fms intronic regulatory element to drive mApple fluorescent protein expression. Csf1r-mApple was robustly expressed in monocyte-macrophage lineage cells in rat bone marrow (BM), peripheral blood, and tissues, with detectable expression in granulocytes and B cells and no evidence of expression in hematopoietic precursors or non-hematopoietic cells. Here, we use the Csf1r-mApple transgene to highlight and dissect the abundance and heterogeneity of rat tissue macrophage populations, and to demonstrate parallel increases in blood monocytes and multiple tissue macrophage populations, including BM, liver, spleen, and lung, in response to CSF1 treatment in vivo. The Csf1r-mApple rat is a novel tool enabling analysis of rat macrophages in situ by direct imaging and providing an additional phenotypic marker to facilitate exploration of rat tissue macrophage phenotypic and functional heterogeneity