New Label-Free Method Identifies Human Eosinophils Using Near-Infrared Light
Scientists have discovered that human eosinophils — immune cells linked to allergies and parasitic infections — produce a uniquely high side scatter signal at 808 nm near-infrared wavelength, enabling their identification without antibody labels. This optical signature was detected using a spectral flow cytometer and showed near-perfect correlation (R = 0.997) with established antibody-based gating methods. The finding could simplify and reduce the cost of diagnosing eosinophil-associated disorders such as asthma, eosinophilic esophagitis, and hypereosinophilic syndrome.
A study posted to bioRxiv reports that human eosinophils exhibit a distinctive high side scatter signal at 808 nm near-infrared wavelength (IRSSC), detectable on a spectral flow cytometer equipped with six SSC detectors. Conventional flow cytometers using 405 nm or 488 nm side scatter struggle to reliably distinguish eosinophils from neutrophils due to overlapping scatter profiles, typically requiring fluorescent antibody labeling for accurate identification. The new approach is entirely label-free, requiring no antibody staining, cell activation, fixation, or permeabilization, which could streamline clinical workflows and reduce reagent costs. The IRSSC signal correlated almost perfectly with the standard CD66b/CD16 antibody gating strategy (R = 0.997), supporting its validity as a standalone biomarker. Notably, the 808 nm signal was absent in murine eosinophils, indicating the phenomenon is human-specific and likely tied to a structural feature unique to human eosinophil granules. The authors propose IRSSC as a robust, reagent-free biomarker with potential applications in both clinical diagnostics and translational immunology research.
What's missing
As a preprint, this study has not yet undergone peer review. The authors note the 808 nm signal is absent in murine eosinophils but do not fully characterize the underlying structural mechanism responsible for the human-specific optical signature. The study's sample size, patient population diversity, and performance across disease states (e.g., activated or degranulated eosinophils in active eosinophilic disease) are not detailed in the abstract, leaving open questions about generalizability. It is also unclear whether existing clinical flow cytometers can be readily upgraded to include 808 nm SSC detectors.
What different sources said
- bioRxivCenter
Label-Free Identification of Human Eosinophils Using 808 nm Side Scatter
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