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Updated: Oct 9, 2025
Author Spotlight: Unveiling the Polyfunctionality and Heterogeneity in Immune Responses
Published on: March 8, 2024
Multiplexed Detection of Secreted Cytokines at near-Molecular Resolution Elucidates Macrophage Polarization
Vanessa Herrera1, Ssu-Chieh Joseph Hsu1, Veena Y Naveen1
1Department of Biomedical Engineering, University of California Irvine, Irvine, California 92697, United States.
Insights
This study developed a highly sensitive quantum dot immunoassay to detect low-level protein secretion from single immune cells. The method revealed heterogeneous macrophage responses, distinguishing subtle pro-healing and pro-inflammatory profiles.
Area of Science:
- * Immunology
- * Cell Biology
- * Nanotechnology
Background:
- * Single-cell protein secretion analysis is crucial for understanding immune cell heterogeneity.
- * Existing methods using microfabricated well arrays lack sensitivity for low-level cytokine detection.
- * Previous work established a quantum dot immunoassay for TNF-α detection at the single-cell level.
Purpose of the Study:
- * To adapt and validate a quantum dot immunoassay for sensitive detection of multiple cytokines (MCP-1, TGF-β, IL-10, TNF-α) from single cells.
- * To quantify the heterogeneous secretion profiles of macrophage cells stimulated with lipopolysaccharide (LPS) and/or interleukin 4 (IL-4).
- * To characterize distinct macrophage phenotypes based on their protein secretion patterns.
Main Methods:
- * Development and application of a quantum dot-based immunoassay with distinct emission spectra for multiplexed cytokine detection.
- * Utilization of microfabricated well arrays for single-cell analysis.
- * Stimulation of macrophage cell lines to induce pro-inflammatory and pro-healing states.
- * Principal component and cluster analysis to classify cell secretion profiles.
Main Results:
- * The quantum dot immunoassay achieved high sensitivity, detecting targets at 1-10 fM (∼1-2 molecules/well).
- * MCP-1 and TGF-β were primarily secreted at high levels, while IL-10 and TNF-α showed lower, heterogeneous secretion.
- * Macrophage phenotypes were classified into distinct profiles, including exclusively pro-inflammatory and mixed pro-healing/pro-inflammatory responses.
Conclusions:
- * The enhanced quantum dot immunoassay enables sensitive detection of low-abundance secreted proteins from single cells.
- * Macrophage responses to stimulation are heterogeneous and exhibit a spectrum of phenotypes rather than discrete states.
- * This technology has potential for analyzing immune cell function in health and disease.
Abstract:
Monitoring the secretion of proteins from single cells can provide important insights into how cells respond to their microenvironment. This is particularly true for immune cells, which can exhibit a large degree of response heterogeneity. Microfabricated well arrays provide a powerful and versatile method to assess the secretion of cytokines, chemokines, and growth factors from single cells, but detection sensitivity has been limited to high levels on the order of 10,000 per cell. Recently, we reported a quantum dot-based immunoassay that lowered the detection limit for the cytokine TNF-α to concentrations to nearly the single-cell level. Here, we adapted this detection method to three additional targets while maintaining high detection sensitivity. Specifically, we detected MCP-1, TGF-β, IL-10, and TNF-α using quantum dots with different emission spectra, each of which displayed a detection threshold in the range of 1-10 fM or ∼1-2 molecules per well. We then quantified secretion of all four proteins from single macrophage cells that were stimulated toward a pro-inflammatory state with lipopolysaccharide (LPS) or toward a pro-healing state with both LPS and interleukin 4 (IL-4). We found that MCP-1 and TGF-β were predominantly secreted at high levels only (>10,000 molecules/cell), while a substantial number of cells secreted IL-10 and TNF-α at lower levels that could only be detected using our method. Subsequent principal component and cluster analysis revealed that secretion profiles could be classified as either exclusively pro-inflammatory, including MCP-1 and/or TNF-α, or more subtle responses displaying both pro-healing and pro-inflammatory characters. Our results highlight the heterogeneous and nondiscrete nature of macrophage phenotypes following in vitro stimulation of a cell line. Future work will focus on expanding the multiplexing capacity by extending emission spectra bandwidth and/or spatially barcoding capture antibodies, as well as evaluating the enhanced detection sensitivity capabilities with normal and diseased immune cell populations in vitro and in vivo.
