Cytokines: From Clinical Significance to Quantification

Abstract

Cytokines are critical mediators that oversee and regulate immune and inflammatory responses via complex networks and serve as biomarkers for many diseases. Quantification of cytokines has significant value in both clinical medicine and biology as the levels provide insights into physiological and pathological processes and can be used to aid diagnosis and treatment. Cytokines and their clinical significance are introduced from the perspective of their pro- and anti-inflammatory effects. Factors affecting cytokines quantification in biological fluids, native levels in different body fluids, sample processing and storage conditions, sensitivity to freeze-thaw, and soluble cytokine receptors are discussed. In addition, recent advances in in vitro and in vivo assays, biosensors based on different signal outputs and intracellular to extracellular protein expression are summarized. Various quantification platforms for high-sensitivity and reliable measurement of cytokines in different scenarios are discussed, and commercially available cytokine assays are compared. A discussion of challenges in the development and advancement of technologies for cytokine quantification that aim to achieve real-time multiplex cytokine analysis for point-of-care situations applicable for both biomedical research and clinical practice are discussed.

Keywords: biosensors; clinical significance; cytokines; in vitro and in vivo assays; quantification.

Figure 1

The outline of contents.

Figure 2

Proposed mechanism of cytokine release syndrome.

Figure 3

Schematic illustration of A) The PhLoC with integrated optical and microfluidic components. Reproduced with permission.^{[ 112 ]} Copyright 2016, American Chemical Society. B) A 3D graphical representation of the unit cell fluidic arrangement during the initial phase of the assay. C) A 3D graphical representation of the unit cell fluidic arrangement during the second phase of the assay, detailing fluidic ports and connections between assay area and electrochemical sensor test cartridge of a Proxim handheld instrument. Reproduced with permission.^{[ 117 ]} Copyright 2018, MDPI.

Figure 4

Schematic illustration of label‐free and labeled biosensors (FI, SPR, SERS, and EC) using antibodies.

Figure 5

Schematic illustration of A) Sensing with microcapsules. Reproduced with permission.^{[ 128 ]} Copyright 2019, American Chemical Society. B) An assay where magnetic fluorescent nanoparticles are captured by antibodies on the biotinylated surface of cells. Reproduced with permission.^{[ 40 ]} Copyright 2019, Elsevier. C) A T cell‐surface aptamer sensor for measuring cytokine secretion at the single‐cell level. Reproduced with permission.^{[ 130 ]} Copyright 2017, The Royal Society of Chemistry. D) The fluorescent method for IFN‐γ detection using three target‐responsive liposomes activated by CHA. Reproduced with permission.^{[ 131 ]} Copyright 2018, The Royal Society of Chemistry.

Figure 6

Schematic illustration of A) CD4+ T‐cell capture and real‐time monitoring of IFN‐g release. Reproduced with permission.^{[ 136 ]} Copyright 2018, Taylor & Francis Group. B) Direct protein patterns for multiplexed cytokine detection. Reproduced with permission.^{[ 137 ]} Copyright 2016, American Chemical Society. C) LSPR microarray chip. Reproduced with the permission.^{[ 24 ]} Copyright 2015, American Chemical Society. D) Integrated localized surface plasmon resonance (LSPR) cytokine detection. Reproduced with permission.^{[ 138 ]} Copyright 2020, MDPI.

Figure 7

Schematic illustration of A) Multiplexed SERS nanotags for the detection of cytokines secreted by lymphoma. Reproduced with permission.^{[ 142 ]} Copyright 2018, Springer. B) Multiplexed SERS nanotags for the detection of cytokines secreted by a lymphoma. Reproduced with permission.^{[ 143 ]} Copyright 2017, Springer. C) Multiplexed SERS nanotags for the detection of cytokines secreted by a lymphoma. Reproduced with permission.^{[ 141 ]} Copyright 2019, American Chemical Society. D) The workflow of the assay on the paper‐based substrate for MCP‐1 and IL‐10 duplex detection. Reproduced with the permission.^{[ 144 ]} Copyright 2019, The Royal Society of Chemistry.

Figure 8

Schematic illustration of A) Steps involved in the preparation of the electrochemical immunosensor for the determination of IFN‐γ. Reproduced with the permission.^{[ 152 ]} Copyright 2020, Elsevier. B) The different steps involved in the preparation of the dual electrochemical immunosensor for multiplexed determination of IL‐1β and TNF‐α. Reproduced with permission.^{[ 153 ]} Copyright 2016, Elsevier. C) The stepwise aptasensor fabrication based on exonuclease‐catalyzed target recycling and surface‐initiated enzymatic polymerization for amplification. Reproduced with the permission.^{[ 155 ]} Copyright 2015, The Royal Society of Chemistry. D) An aptamer‐based electrochemical sensor for IFN‐γ. Reproduced with the permission.^{[ 156 ]} Copyright 2017, American Chemical Society.

Figure 9

Schematic illustration of A) The CRISPR/Cas13a signal amplification system. Reproduced with the permission.^{[ 160 ]} Copyright 2019, American Chemical Society. B) The proposed method for protein detection, utilizing VEGF as an example. Reproduced with the permission.^{[ 164 ]} Copyright 2016, Elsevier.

Figure 10

Luminex technique and general principles. Reproduced with the permission.^{[ 176 ]} Copyright 2015, The Society for Investigative Dermatology.