Inflammation is a complex biological response of the body’s immune system to harmful stimuli, such as pathogens, damaged cells, or irritants. It is a protective mechanism that involves immune cells, blood vessels, and molecular mediators which work together to eliminate the initial cause of cell injury, clear out damaged cells, and tissues, and establish a repair process. Among all molecular mediators involved, cytokines play a pivotal role in the orchestration of the inflammatory response. These small proteins are secreted by various immune cells and affect the behavior of other cells by binding to specific receptors on their surface. Cytokines can be pro-inflammatory, driving the inflammation process, or anti-inflammatory, mitigating the response to prevent excessive damage and each cytokine have its own role to play. The balance and secretion of cytokines determines the outcome of the inflammatory response, which can range from resolution and healing to chronic inflammation and tissue destruction. Understanding the dynamics of cytokine secretion during inflammation is crucial for developing therapeutic interventions for a wide array of inflammatory diseases.

 

The critical role of mouse models in inflammatory cytokine research

The immune system’s response to a pathogen is a complex process and the use of animal models stands as a cornerstone in the study of inflammatory cytokines, providing invaluable information. The advantages of animal models for the study of inflammation include:

• Physiological relevance: Animal models offer a whole-organism context, incomparable with in vitro assay, that closely mimics human physiological processes. This allows for a more accurate representation of how inflammatory cytokines interact within a living system, providing insights that are more relevant and translatable to human conditions.
• Controlled experimental condition: These models offer a controlled environment, such as the genetic background, the environment, and the timing and dosage of pathogen exposure. This control is crucial for understanding the specific roles and mechanisms of cytokines in the immune system and for the reproducibility of studies.
• Mimic human inflammatory diseases: There are numerous animal models that replicate human inflammatory diseases ranging from genetic modification to the injection of pathogens or the use of chemical agents. Thus, mouse models can reproduce diseases such as rheumatoid arthritis, inflammatory bowel disease, and psoriasis.

Figure 1: Experimental model for studying Systemic Inflammatory Response and Sepsis (SIRS) in humans and the role of pro-inflammatory cytokines. Lipopolysaccharide (LPS), a major component of the outer membrane of gram-negative bacteria, is administrated in the peritoneum and results in general inflammation. Cytokines are detected in the bloodstream.

 

The tools to explore the cytokine storm

There are several tools and techniques to explore and measure cytokine storm, a hyperinflammatory state that develops due to excessive cytokine release in response to an infection. Because this response involves many different cytokines, a multiplexed analysis is required to obtain accurate quantification. Two relevant techniques are described below:

• MSD (Meso Scale Discovery^®) is a method based on MULTI-ARRAY^® technology, which combines electrochemiluminescence detection using labels that emit light when electrochemically stimulated and patterned arrays.

Figure 2: Biotinylated capture antibodies are immobilized on a U-plex plate through coupling to a U-plex linker. The analytes in the sample bind to the capture reagents. Detection antibodies conjugated with electro-chemiluminescent labels (SULFO-TAG) bind to the analytes to complete the sandwich immunoassay. The instrument (MSD™ QuickPlex SQ 120MM) detects the intensity of emitted light and provides a quantitative measure of each analyte. Source: https://www.mesoscale.com/

• LEGENDplex™ allows for cytokine quantification in a multiplex assay by utilizing beads pre-coated with antibodies for their intended target. Analysis can be carried out using most common flow cytometers.

Figure 3: Beads are differentiated by size and internal fluorescence intensities. Each bead set is conjugated with a specific antibody on its surface and serves as the capture beads for a particular analyte. Biotinylated detection antibody and Streptavidin-PE complete the reaction. On a flow cytometer, analyte-specific populations can be segregated by size and the analyte concentration is determined using fluorescence intensity. Source: https://www.biolegend.com/en-us/immunoassays/legendplex

Both tools are used for the quantification of pro-inflammatory cytokines, providing high sensitivity and a broad dynamic range for the detection of these critical immune markers. Their multiplexing capabilities allow for the simultaneous measurement of multiple cytokines in a single sample, streamlining the analysis and improving the efficiency of inflammation-related research.

 

Case study: Using MSD technology^® to measure Eotaxin, an eosinophil-specific chemokine

Eotaxin, also known as CCL11 (C-C motif chemokine ligand 11), is a chemokine involved in inflammation, particularly in the recruitment of eosinophils, a type of white blood cell. During inflammatory responses, eotaxin is secreted by various types of cells, including endothelial cells, fibroblasts, and epithelial cells, in response to cytokines such as IL-4 and IL-13, which are released during allergic reactions or other types of inflammation.

Figure 4: The concentration of eotaxin in mice serum after intra-peritoneal injection of increasing doses of LPS. The chemokine was analyzed by MSD technology^®. The elevation in eotaxin levels is proportional to the amount of administered pathogenic agent. This secretion becomes effective 3 hours post-injection, and the concentration of eotaxin remains sustained until the animals are sacrificed at 6 hours.

Numerous other cytokines, such as IL-1β, IL-6, IFN-γor TNF-α, were assessed during the sepsis shock in our mouse model. The multiplex measurement of these pro-inflammatory cytokines was carried out with the MSD technology^® and the LegendPlex™ to compare their sensitivity and methodologies. To discover all the facets of this study, please click on this link, which will take you to the full research paper.

 

References

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Lewis AJ, Seymour CW, Rosengart MR. Current Murine Models of Sepsis. Surg Infect (Larchmt). 2016 Aug;17(4):385-93. doi: 10.1089/sur.2016.021. Epub 2016 Jun 15

Dabitao D, Margolick JB, Lopez J, Bream JH. Multiplex measurement of proinflammatory cytokines in human serum: comparison of the Meso Scale Discovery electrochemiluminescence assay and the Cytometric Bead Array. J Immunol Methods. 2011 Sep 30;372(1-2):71-7. doi: 10.1016/j.jim.2011.06.033. Epub 2011 Jul 18.

Williams TJ. Eotaxin-1 (CCL11). Front Immunol. 2015 Feb 24;6:84. doi: 10.3389/fimmu.2015.00084.