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0 Q&A 2009 Views Feb 5, 2022

Extracellular microvesicles (MVs) are released into the circulation in large numbers during acute systemic inflammation, yet little is known of their intravascular cell/tissue-specific interactions under these conditions. We recently described a dramatic increase in the uptake of intravenously injected MVs by monocytes marginated within the pulmonary vasculature, in a mouse model of low-dose lipopolysaccharide-induced systemic inflammation. To investigate the mechanisms of enhanced MV uptake by monocytes, we developed an in vitro model using in vivo derived monocytes. Although mouse blood is a convenient source, monocyte numbers are too low for in vitro experimentation. In contrast, differentiated bone marrow monocytes are abundant, but they are rapidly mobilized during systemic inflammation, and thus no longer available. Instead, we developed a protocol using marginated monocytes from the pulmonary vasculature as an anatomically relevant and abundant source. Mice are sacrificed by terminal anesthesia, the lungs inflated and perfused via the pulmonary artery. Perfusate cell populations are evaluated by flow cytometry, combined with in vitro generated fluorescently labelled MVs, and incubated in suspension for up to one hour. Washed cells are analyzed by flow cytometry to quantify MV uptake and confocal microscopy to localize MVs within cells (O'Dea et al., 2020). Using this perfusion-based method, substantial numbers of marginated pulmonary vascular monocytes are recovered, allowing multiple in vitro tests to be performed from a single mouse donor. As MV uptake profiles were comparable to those observed in vivo, this method is suitable for physiologically relevant high throughput mechanistic studies on mouse monocytes under in vitro conditions.

Graphic abstract:

Figure 1. Schematic of lung perfusate cell harvest and co-incubation with in vitro generated MVs.
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0 Q&A 2245 Views Aug 20, 2021

Recent advances in single-cell RNA-sequencing (scRNA-seq) technologies provide unprecedented opportunities to identify new cell types and characterize cell states. One of the most important requirements for performing scRNA-seq is to obtain high-quality single cells in suspension. Recently, we used this approach to characterize Drosophila blood cells (hemocytes). Here, we provide a detailed protocol for obtaining single hemocytes in suspension, which can be used for microfluidics-based scRNA-seq platforms. This protocol involves the simple bleeding of third instar larvae and the subsequent purification of the hemolymph using either Optiprep-based gradient centrifugation or traditional centrifugation methods to obtain single hemocytes of high quality for scRNA-seq. Importantly, this method for single-hemocyte preparation is straightforward and reproducible, with negligible issues associated with cell viability as the entire procedure involves no enzymatic dissociation.

Graphic abstract:

Workflow for the preparation of Drosophila larval blood cells in suspension. Hemocytes (blood cells) of the sessile and circulatory compartments of larvae are derived by simple bleeding and purification using gradient centrifugation. Blood cells are counted and subsequently encapsulated by microfluidics-based scRNA-seq platforms. Blood cells represented in the schematic are derived from third instar larvae of the genotype Hemolectin-GAL4.Delta, UAS-2xEGFP (BDSC stock #30140).

0 Q&A 3836 Views Jul 20, 2021

Microglia are a unique type of tissue-resident innate immune cell found within the brain, spinal cord, and retina. In the healthy nervous system, their main functions are to defend the tissue against infectious microbes, support neuronal networks through synapse remodeling, and clear extracellular debris and dying cells through phagocytosis. Many existing microglia isolation protocols require the use of enzymatic tissue digestion or magnetic bead-based isolation steps, which increase both the time and cost of these procedures and introduce variability to the experiment. Here, we report a protocol to generate single-cell suspensions from freshly harvested murine brains or spinal cords, which efficiently dissociates tissue and removes myelin debris through simple mechanical dissociation and density centrifugation and can be applied to rat and non-human primate tissues. We further describe the importance of including empty channels in downstream flow cytometry analyses of microglia single-cell suspensions to accurately assess the expression of protein targets in this highly autofluorescent cell type. This methodology ensures that observed fluorescence signals are not incorrectly attributed to the protein target of interest by appropriately taking into account the unique autofluorescence of this cell type, a phenomenon already present in young animals and that increases with aging to levels that are comparable to those observed with antibodies against highly abundant antigens.

0 Q&A 4660 Views May 20, 2020
Mycobacterium tuberculosis (Mtb) is transmitted by aerosol and can cause serious bacterial infection in the lung that can be fatal if left untreated. Mtb is now the leading cause of death worldwide by an infectious agent. Characterizing the early events of in vivo infection following aerosol challenge is critical for understanding how innate immune cells respond to infection but is technically challenging due to the small number of bacteria that initially infect the lung. Previous studies either evaluated Mtb-infected cells at later stages of infection when the number of bacteria in the lung is much higher or used in vitro model systems to assess the response of myeloid cells to Mtb. Here, we describe a method that uses fluorescent bacteria, a high-dose aerosol infection model, and flow cytometry to track Mtb-infected cells in the lung immediately following aerosol infection and fluorescence-activated cell sorting (FACS) to isolate naïve, bystander, and Mtb-infected cells for downstream applications, including RNA-sequencing. This protocol provides the ability to monitor Mtb-infection and cell-specific responses within the context of the lung environment, which is known to modulate the function of both resident and recruited populations. Using this protocol, we discovered that alveolar macrophages respond to Mtb infection in vivo by up-regulating a cell protective transcriptional response that is regulated by the transcription factor Nrf2 and is detrimental to early control of the bacteria.
3 Q&A 30566 Views May 20, 2015
In homeostasis, the liver is critical for the metabolism of nutrients including sugars, lipids, proteins and iron, for the clearance of toxins, and to induce immune tolerance to gut-derived antigens. These functions predispose the liver to infection by blood-borne pathogens, and to a variety of diseases ranging from toxin and medication-induced disorders (CCl4, acetaminophen) to metabolic disorders (steatohepatitis, alcoholic liver disease, biliary obstruction, cholestasis) or autoimmunity. Chronic liver injury often progresses to life threatening fibrosis and can end in liver cirrhosis and hepatocellular carcinoma (Pellicoro et al., 2014).

The liver contains parenchymal cells or hepatocytes that make up the majority of hepatic cells. It also contains non-parenchymal structural cells such as sinusoidal endothelial cells and a large number of non-parenchymal innate immune cells, mainly monocytes, neutrophils, macrophages, DCs, NK and NKT cells that can trigger an adaptive immune response in the case of infections or other pathogenic insults (Jenne and Kubes, 2013). How this immune response is regulated determines the extent of acute and chronic liver injury (Stijlemans et al., 2014). In this context, liver macrophages have been demonstrated to play central but divergent (from initiating to resolving) functions in liver injury (Sica et al., 2014). It has become clear in the last years that hepatic macrophages consist of two classes, tissue-resident macrophages, the Kupffer cells (KCs) originating from yolk sac/fetal liver progenitors and tissue-infiltrating macrophages originating from bone marrow-derived Ly6CHi monocytes (Jinhoux and Jung, 2014; Tacke and Zimmerman, 2014). Distinguishing the activities of KCs from those of monocyte-derived macrophages during liver injury or repair is currently a frontline research topic in the macrophage field. Indeed, considering that clinical management of liver failure remains problematic, a better understanding of the immune mechanisms regulating liver injury is expected to allow the development of new therapeutic modalities. Here, we describe an isolation technique for liver non-parenchymal polymorphonuclear (PMN) and mononuclear myeloid cells permitting their molecular and functional characterization.

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