Immunology

During adaptive immune responses, germinal centers (GC) appear as transient microstructures, in which antigen-specific B and T cells interact with each other. Because only the antigen-activated B and T cells, such as Plasmablasts or follicular T helper (Tfh) cells, are present in GC, the in depth-analysis of GC is of great interest. To identify the cells that reside within GC, the majority of studies use the expression of specific surface molecules for analysis by flow cytometry. To do so, the tissue has to be disrupted for the preparation of single-cell suspensions. Thereby, the local information regarding neighborhoods of B cells and T cells and their potential interaction is lost. To study GC in vivo within their original microenvironment, we established a protocol for the isolation of GC by laser microdissection. To enable the identification of GC for subsequent transcriptomic analysis, the degradation of mRNA was diminished by using frozen tissues and by establishing a rapid staining protocol. This procedure enables histological and transcriptomic analysis of individual GC even within one lymphoid organ.

When the body mounts an immune response against a foreign pathogen, the adaptive arm of the immune system relies upon clonal expansion of antigen-specific T cell populations to exercise acquired effector and cytotoxic functions to clear it. However, T cell expansion must be modulated to effectively combat the perceived threat without inducing excessive collateral damage to host tissues. Restimulation-induced cell death (RICD) is an apoptotic program triggered in activated T cells when an abundance of antigen and IL-2 are present, imposing a negative feedback mechanism that constrains the growing T cell population. This autoregulatory process can be detected via increases in caspase activation, Annexin V binding, and loss of mitochondrial membrane potential. However, simple changes in T cell viability through flow cytometric analysis can reliably measure RICD sensitivity in response to T-cell receptor (TCR) restimulation. This protocol describes the in vitro polyclonal activation, expansion, and restimulation of human primary T cells isolated from donor peripheral blood mononuclear cells (PBMC). This simple procedure allows for accurate quantification of RICD via flow cytometry. We also describe strategies for interrogating the role of specific proteins and pathways that may alter RICD sensitivity. This straightforward protocol provides a quick and dependable tool to track RICD sensitivity in culture over time while probing critical factors that control the magnitude and longevity of an adaptive immune response.

Graphic abstract:

In-vitro simulation of restimulation-induced cell death in activated human T cells.

Peripheral blood mononuclear cell (PBMC) isolation is commonly done via density gradient centrifugation over Ficoll-Hypaque, a labor-intensive procedure that requires skilled technicians and can contribute to sample variability. Cellular Preparation Tubes (CPTs) are Vacutainer blood draw tubes that contain Ficoll-Hypaque and a gel plug that separates the Ficoll solution from the blood to be drawn. Once blood is drawn into CPTs, they can be centrifuged to separate the PBMC, then shipped (if desired) to a processing lab. The processing lab removes the PBMC from the upper compartment of the tube (above the gel plug), washes the PBMC, and can cryopreserve them using DMSO-containing media, as detailed in this protocol.

Infiltration of leukocytes into joints is one of the main features of autoimmune inflammatory arthritis. Here, we describe the protocol for isolation of joint-infiltrating cells in mice. This protocol is useful to analyze cell surface antigens and intracellular cytokines by flow cytometry.

Atherosclerosis is a chronic inflammatory disease of the arterial wall characterized by lipid deposition, plaque formation, and immune cell infiltration. Innate and adaptive immune cells infiltrate the artery during development of the disease. Moreover, advanced disease leads to formation of artery tertiary lymphoid organs in the adventitia (Grabner et al., 2009; Hu et al., 2015). Various and diverse types of immune cells have been identified in the aorta adventitia vs atherosclerotic plaques (Elewa et al., 2016; Galkina et al., 2006; Lotzer et al., 2010; Mohanta et al., 2016; Mohanta et al., 2014; Moos et al., 2005; Srikakulapu et al., 2016; Zhao et al., 2004). There are conflicting reports on the number and subtypes of immune cells in the aorta depending on the age of the animals, the protocol that is used to obtain single cell suspensions, and the dietary conditions of the mice (Campbell et al., 2012; Clement et al., 2015; Galkina et al., 2006; Kyaw et al., 2012). The number of immune cells in the aorta differs as much as tenfold using different protocols (Butcher et al., 2012; Galkina et al., 2006; Gjurich et al., 2015; Grabner et al., 2009; Hu et al., 2015). These discrepant results call for a protocol that robustly documents bona fide aorta cells rather than those in the surrounding tissues or blood. Critical methodological hurdles include the removal of adjacent adipose tissue and small paraaortic lymph nodes lining the entire aortic tree that are not visible by the naked eye. A dissection microscope is therefore recommended. Moreover protocols of aorta preparations should ascertain that lymphocyte aggregates referred to as fat associated lymphoid clusters (FALCs) (Benezech et al., 2015; Elewa et al., 2015) that are often present at the border between the adipose tissue and the adventitia are removed before enzyme digestion. We propose - besides other approaches (Hu et al., 2015; Mohanta et al., 2014) - a combination of immunohistochemical staining and fluorescence activated cell sorter (FACS) analyses from single cell suspensions to quantify the cells of interest. This protocol describes isolation of single cells from mouse aorta for FACS and other analysis.