CD11c‐positive cells from brain, spleen, lung, and liver exhibit site‐specific immune phenotypes and plastically adapt to new environments

Abstract

The brain's immune privilege has been also attributed to the lack of dendritic cells (DC) within its parenchyma and the adjacent meninges, an assumption, which implies maintenance of antigens rather than their presentation in lymphoid organs. Using mice transcribing the green fluorescent protein under the promoter of the DC marker CD11c (itgax), we identified a juxtavascular population of cells expressing this DC marker and demonstrated their origin from bone marrow and local microglia. We now phenotypically compared this population with CD11c/CD45 double-positive cells from lung, liver, and spleen in healthy mice using seven-color flow cytometry. We identified unique, site-specific expression patterns of F4/80, CD80, CD86, CX3CR1, CCR2, FLT3, CD103, and MHC-II. Furthermore, we observed the two known CD45-positive populations (CD45(high) and CD45(int) ) in the brain, whereas liver, lung, and spleen exhibited a homogeneous CD45(high) population. CD11c-positive microglia lacked MHC-II expression and CD45(high) /CD11c-positive cells from the brain have a lower percentage of MHC-II-positive cells. To test whether phenotypical differences are fixed by origin or specifically develop due to environmental factors, we transplanted brain and spleen mononuclear cells on organotypic slice cultures from brain (OHSC) and spleen (OSSC). We demonstrate that adaption and ramification of MHC-II-positive splenocytes is paralleled by down-regulation of MHC-II, whereas brain-derived mononuclear cells neither ramified nor up-regulated MHC-II in OSSCs. Thus, brain-derived mononuclear cells maintain their MHC-II-negative phenotype within the environment of an immune organ. Intraparenchymal CD11c-positive cells share immunophenotypical characteristics of DCs from other organs but remain unique for their low MHC-II expression.

Neurons exhibit Lyz2 promoter activity in vivo: Implications for using LysM‐Cre mice in myeloid cell research

“…1A, C, and E). Since fixation could impact on detection of fluorescent proteins, we confirmed our data using flow cytometry of acutely isolated living microglia of the entire forebrain defined by CD45 intermediate expression as described previously [10]. In accordance with image quantification data, the average of tdTomato-positive microglia was 10.7% (n = 4; Supporting Information Fig.…”

“…Furthermore, LysM-Cre mice have been used to genetically target myeloid cells or microglia (Supporting Information refs. [6][7][8][9][10]). However, recently LysM-Cre mice have been controversially discussed to target microglia [7,8].…”

“…In 2014 and 2015 at least six publications used LysM-Cre mice and analyzed effects on the central nervous system (Supporting Information refs. [10][11][12][13][14][15][16]). We here show that putative myeloid targeting using LysM-Cre mice would also affect a large subset of neurons, which may even be more pronounced under pathological conditions.…”

Caspase-8 inhibition represses initial human monocyte activation in septic shock model

“…For this purpose, bone marrow monocytes were isolated from mice lacking caspase-8 in the myeloid cell line (Caspase-8 f/f LysMCre +/− ). These mice, which were generated using flox-Cre technology, have been previously documented in studies on microglial and myeloid cells [29–34]. Monocytes were purified from the bone marrow by negative selection, as the isolated monocytes have been previously shown to be equivalent to blood monocytes [35].…”

Targeting of the class II transactivator attenuates inflammation and neurodegeneration in an alpha-synuclein model of Parkinson’s disease

“…Additionally, a number of papers have reported fundamental differences in the genetic profiles of cultured primary microglia compared to their freshly isolated adult counterparts [37] indicating that in vitro, microglia may not achieve a full resting state. Furthermore, it is important to note that microglia in a healthy mouse brain have very low expression of MHCII at baseline [14, 38, 39]. Therefore, it is difficult to know whether the in vitro expression at baseline is due to compensatory transcriptional pathways, intrinsic differences between in vitro and in vivo cells, or baseline biological differences in activation status between WT and CIITA knock-out.…”