Immunology

Chemically induced murine colitis models are widely used to understand intestinal homeostasis and inflammatory responses during acute and chronic gut inflammation, such as inflammatory bowel disease (IBD). Resident populations of immune cells, together with those recruited during an inflammatory response, maintain intestinal immunity by mounting an effective immune response to enteropathogenic microbes while at the same time maintaining tolerance against commensals. To better understand the disease mechanism, studying different immune cell populations and their dynamic changes during infection and inflammation is essential. However, isolating healthy and viable immune populations, particularly hyperactivated neutrophils and macrophages from the inflamed gut (i.e., active disease site), is challenging as tissues are usually subjected to rigorous enzymatic digestion for an extended period. Here, we describe a method that uses a cell dissociator (Medimachine II from Syntec International) to separate intestinal tissue after short enzymatic digestion to obtain a single-cell suspension. This technique facilitates the isolation of immune cells from mouse intestinal tissues in high quantity and with superior viability in a very short time frame. This protocol delivers 80%–90% cell viability, which is 1.5 to 2-fold higher than conventional methods of isolating cells from inflamed mouse colons. The composition, phenotype, activation state, and gene expression profile of cells isolated using this protocol can be assessed by using multiple methods, including, but not limited to, flow cytometry, quantitative PCR, immunoblotting, mass spectrometry, single-cell RNA sequencing, and functional readouts such as reactive oxygen species (ROS) production.

Neutrophil-derived microvesicles (NDMVs) are liberated by neutrophils upon cell activation by molecules. Once activated, neutrophils are primarily involved in acute inflammation; however, the microvesicles they produce are largely anti-inflammatory. NDMVs have been shown to protect cartilage during inflammatory arthritis. They exert these effects by inhibiting or affecting the function of target cells, including macrophages. NDMVs have the potential to act as disease-modifying agents, especially for inflammatory diseases. This protocol describes a method using differential centrifugation to separate neutrophils from whole human blood. Subsequently, neutrophils are identified by cytospin and Wright’s staining, and then the NDMVs are isolated using differential centrifugation.

The study of human neutrophils in vitro is challenging due to their short half-life and propensity for activation. However, with careful handling and manipulation in the laboratory, they can be a powerful tool to investigate immune responses in health and disease. Here we describe a method for the isolation of human neutrophils from peripheral blood samples, followed by a high-throughput screen to assess the efficacy of a library of compounds in inducing neutrophil apoptosis, which may have therapeutic potential in neutrophil-driven diseases. This protocol is based on previously-published neutrophil isolation methods utilizing Dextran sedimentation of red blood cells followed by the separation of granulocytes with plasma/Percoll discontinuous gradient centrifugation. Yields of ~1 x 10⁶ neutrophils per millilitre of blood, and purities of > 95% neutrophils are typical. Neutrophils are treated with a library of kinase inhibitors, followed by flow cytometry to assess the rate of neutrophil apoptosis. This protocol allows for the high-throughput screening of primary human immune cells to identify compounds with a potential to modify neutrophil function, and could be modified to assess other phenotypes if required.

Neutrophils are critical immune cells that protect our body against invading pathogens. They generate antibacterial DNA structures called neutrophil extracellular traps (NET). Recently we identified a new mechanism that enables NET formation. We observed that following recognition of lipopolysaccharides, inflammatory caspases cleave Gasdermin D and enable NET generation (Chen et al., 2018). This protocol describes how we purify neutrophil nuclei to visualize NET formation by live microscopy. After neutrophil purification from murine bone marrow, neutrophils are lysed in a hypotonic buffer using a nitrogen cavitation device to prevent lysis of neutrophil granules and subsequent contamination by granules proteases. Lysed neutrophils are then centrifuged, and nuclei are counted. The protocol described here is straightforward and enables the study of early changes happening in the nuclei of neutrophils undergoing NETosis with limited contamination by granule proteases.