Immunology

The skin plays an important role in protecting the body from pathogens and chemicals in the external environment. Upon injury, a healing program is rapidly initiated and involves extensive intercellular communication to restore tissue homeostasis. The deregulation of this crosstalk can lead to abnormal healing processes and is the foundation of many skin diseases. A relatively overlooked cell type that nevertheless plays critical roles in skin homeostasis, wound repair, and disease is the dendritic epidermal T cells (DETCs), which are also called γδT-cells. Given their varied roles in both physiological and pathological scenarios, interest in the regulation and function of DETCs has substantially increased. Moreover, their ability to regulate other immune cells has garnered substantial attention for their potential role as immunomodulators and in immunotherapies. In this article, we describe a protocol to isolate and culture DETCs and analyse them in vivo within the skin. These approaches will facilitate the investigation of their crosstalk with other cutaneous cells and the mechanisms by which they influence the status of the skin.

Graphic abstract:

Overall workflow to analyse DETCs in vitro and in vivo.

Clearance of apoptotic cells by macrophages is critical to ensuring cellular homeostasis and suppression of autoimmunity. Macrophage recognition of apoptotic cells triggers an anti-inflammatory response, which is mediated by the release of IL-10, TGF-β etc. with concurrent inhibition of pro-inflammatory cytokines (such as TNFα, IL-12, IL-1β). To characterize cytokine profile produced by macrophages during phagocytosis of apoptotic cells, we developed an effective, more physiologic system using isolated murine peritoneal macrophages and T-lymphocyte cell line Jurkat as a source of apoptotic cells. Apoptosis of Jurkat cells is induced with staurosporine, a protein kinase C (PKC) inhibitor and detected by Annexin V/propidium iodide staining. This in vitro assay demonstrates that murine peritoneal macrophages produce large amounts of IL-10 following exposure to apoptotic Jurkat cells.

Alveolar macrophages (AM) are tissue-resident macrophages that colonize the lung around birth and can self-maintain long-term in an adult organism without contribution of monocytes. AM are located in the pulmonary alveoli and can be harvested by washing the lungs using the method of bronchoalveolar lavage (BAL). Here, we compared different conditions of BAL to obtain high yields of murine AM for in vitro culture and expansion of AM. In addition, we describe specific culture conditions, under which AM proliferate long-term in liquid culture in the presence of granulocyte-macrophage colony-stimulating factor. This method can be used to obtain large numbers of AM for in vivo transplantation or for in vitro experiments with primary mouse macrophages.

In this protocol, we describe the method for isolating highly pure primary alveolar epithelial type II (ATII) cells from lungs of naïve mice. The method combines negative selection for a variety of lineage markers along with positive selection for EpCAM, a pan-epithelial cell marker. This method yields 2-3 x 10⁶ ATII cells per mouse lung. The cell preps are highly pure and viable and can be used for genomic or proteomic analyses or cultured ex vivo to understand their roles in various biological processes.

During the last 20 years intestinal mesenchymal cells (IMCs) have emerged as an important cell type that plays a central role in intestinal development and homeostasis, by providing both structural support and growth regulatory elements. IMCs also actively participate in wound healing responses, thus regulating pathologic conditions such as tissue repair, inflammation, fibrosis and carcinogenesis (Powell et al., 2011). We have recently demonstrated that intestinal mesenchymal-specific signals play important in vivo physiological roles in intestinal inflammation and carcinogenesis (Koliaraki et al., 2012; Roulis et al., 2014; Koliaraki et al., 2015). Here we describe the enzymatic method used for the isolation and culture of mesenchymal cells from the adult mouse intestine.

Culture of mouse embryonic fibroblast (MEF) cells represents a powerful system to test gene function due to their easy accessibility, rapid growth rates, and the possibility of a large number of experiments. Fibroblasts are a group of heterogeneous resident cells of mesenchymal origin that have various locations, diverse appearances and distinctive activities. Because of their ubiquitous distribution as tissue cells, these cells are poised to respond to factors released by newly activated innate immune cells, thus becoming a useful tool to study inflammation and immunity. Here, we describe procedures for mouse embryonic fibroblast cell isolation, primary culture, and stimulation. Specifically, we have optimized a step of serum starvation prior to stimulation. This step is necessary to maintain the quiescent status of these cells before they are exposed to pro-inflammatory stimuli for optimal responses. As shown in our previous studies, these mouse fibroblasts do not express Tnf, Csf2 or Il2 mRNAs at levels readily detectable by routine northern blotting techniques (Lai WS et al., 2006).

Small intestinal organoids, otherwise known as enteroids, have become an increasingly utilized model for intestinal biology in vitro as they recapitulate the various epithelial cells within the intestinal crypt (Mahe et al., 2013; Sato et al., 2009). Assessment of growth dynamics within these cultures is an important step to understanding how alterations in gene expression, treatment with protective and toxic agents, and genetic mutations alter properties essential for crypt growth and survival as well as the stem cell properties of the individual cells within the crypt. This protocol describes a method of visualization of proliferating cells within the crypt in three dimensions (Barrett et al., 2015). Whole-mount proliferation staining of enteroids using EdU incorporation enables the researcher to view all proliferating cells within the enteroid as opposed to obtaining growth information in thin slices as would be seen with embedding and sectioning, ensuring a true representation of proliferation from the stem cell compartment to the terminally differentiated cells of the crypt.

The islets of Langerhans are clusters of endocrine cells located within the pancreas. Insulin-producing beta cells are the major cell type within islets, with glucagon-producing alpha cells and somatostatin-producing delta cells the other major cell types. The beta cells are the target of immune-mediated destruction in type 1 diabetes (Graham et al., 2012). Failure of beta cell function accompanied by loss of beta cell mass is also a feature of type 2 diabetes (Wali et al., 2013). Therefore studying the biology of pancreatic islets is important to understand the pathogenesis of diabetes and to develop new therapies. Here we describe the isolation of mouse islets. This requires gentle enzymatic and mechanical digestion of the exocrine tissue and density gradient separation (Chong et al., 2004; Liu and Shapiro, 1995; Thomas et al., 1998). We then describe how islets can be cultured whole or dispersed into single cells for use in a variety of in vitro and in vivo analyses. Using this protocol reliably results in the isolation of 200-400 islets, depending on the strain of mouse.

Subtypes of innate lymphoid cells (ILC), defined based on their cytokine secretion profiles and transcription factor expression, are important for host protection from pathogens and maintaining tissue homeostasis. ILCs develop from common lymphoid progenitors (CLP) in the bone marrow. Using the methods described here, we have previously shown that loss of the transcriptional regulator TOX (Thymocyte-selection associated HMG-box protein) leads to specific changes in ILC development and differentiation. Here, we describe how to obtain ILCs from in vivo isolated CLP grown in vitro.

Dendritic cells (DC) are antigen-presenting cells, which play a critical role in the regulation of the adaptive immune response. They act as a bridge between the innate and the adaptive immune systems. An approach to study their function and potentiality is to generate DC-like cells by culturing CD14⁺ monocyte-enriched peripheral blood mononuclear cells (PBMC). In the presence of GM-CSF and IL-4, these cultures give rise to large numbers of DC-like cells. Generating human-DC from PBMC is a useful tool to study biological functions of human DC.