==== Front Clin Transl Allergy Clin Transl Allergy 10.1002/(ISSN)2045-7022 CLT2 Clinical and Translational Allergy 2045-7022 John Wiley and Sons Inc. Hoboken 10.1002/clt2.12275 CLT212275 Correspondence Correspondence Charcot‐Leyden crystals in tissues Sasaki Tomoko 1 Suzaki Isao 2 Ueki Shigeharu https://orcid.org/0000-0002-3537-7735 1 shigeharu.ueki@gmail.com 1 Department of General Internal Medicine and Clinical Laboratory Medicine Akita University Graduate School of Medicine Akita Japan 2 Department of Otorhinolaryngology Head and Neck Surgery School of Medicine Showa University Tokyo Japan * Correspondence Shigeharu Ueki, Department of General Internal Medicine and Clinical Laboratory Medicine, Akita University Graduate School of Medicine, 1‐1‐1 Hondo, Akita 010‐8543, Japan. Email: shigeharu.ueki@gmail.com 01 7 2023 7 2023 13 7 10.1002/clt2.v13.7 e12275© 2023 The Authors. Clinical and Translational Allergy published by John Wiley & Sons Ltd on behalf of European Academy of Allergy and Clinical Immunology. https://creativecommons.org/licenses/by/4.0/ This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. ENT eosinophil immunology rhinosinusitis Japan Society for the Promotion of Science 10.13039/501100001691 20H03832 20K08794 21K07833 21K08434 source-schema-version-number2.0 cover-dateJuly 2023 details-of-publishers-convertorConverter:WILEY_ML3GV2_TO_JATSPMC version:6.3.0 mode:remove_FC converted:01.07.2023 ==== Body pmcTo the Editor, We read with interest the paper by Chen et al. entitled “Predictive significance of Charcot‐Leyden crystal (CLC) structures for nasal polyp recurrence”. 1 CLCs are formed when galectin‐10 crystallizes intracellularly or extracellularly through eosinophil ETosis, an active cell death process involving the disruption of the cell nucleus and plasma membrane to release web‐like chromatin structures. 2 , 3 Intact eosinophil granules are also released during this process, typically characterized by the presence of cell‐free eosinophil granules (Cfegs). 2 In the H&E‐stained specimens shown by Chen et al., most eosinophils in the nasal polyp tissues have barely retained their morphology, and both cell disruption with web‐like nuclear contents and Cfegs are clearly visible. Meanwhile, the lack of concordance between eosinophil counts and CLCs in the tissues may have arisen because cytolytic eosinophils are not evaluated. 4 Not only the cytotoxic granule proteins released by ETosis but also the presence of the crystals themselves may enhance the exacerbation loop of inflammation. 5 Therefore, it is significant to focus on the presence of CLCs in the tissues. We previously examined the nasal polyp histology in patients with eosinophilic chronic rhinosinusitis and found that CLCs were present in more than half of the patients with moderate to severe disease based on the JESREC criteria. 6 In the JESREC study, the recurrence rates were 31.1% in patients with moderate disease and 51.8% in patients with severe disease. 6 These findings are generally consistent with the results of Chen et al. Nasal polyps are clinically easy to obtain for examination, and pathologists should be encouraged to report the presence of CLCs to clinicians. However, there are several associated problems. First, the tissue sections are not uniform and the results can differ markedly depending on the field observed. Second, depending on the angle at which the crystals are sectioned, the characteristic needle‐like structures may be difficult to identify. Third, CLCs are difficult to distinguish from other eosinophilic structures, including collagen fibers. As shown in Figure 1, CLCs can be easily observed by immunofluorescence staining for galectin‐10, 3 but this is a time‐consuming and labor‐intensive process. Charcot‐Leyden crystals have also been observed in tissues from patients with other eosinophilic diseases, but their clinical significance has not been fully investigated. It will be interesting to determine whether similar trends are present in other diseases and whether CLCs can predict the efficacy of eosinophil‐targeted therapies. FIGURE 1 The same nasal polyp section from a patient with eosinophilic chronic rhinosinusitis was evaluated by (left) H&E staining and (right) immunofluorescence staining for galectin‐10 (green) and DNA (blue). Abundant Charcot‐Leyden crystals (CLCs) were clearly observed as galectin‐10‐positive structures. Written informed consent was obtained from a patient in accordance with the principles laid out in the Declaration of Helsinki and using Institutional Review Board‐approved protocols. Author Contributions Tomoko Sasaki: Investigation (Equal); Validation (Equal); Visualization (Equal). Isao Suzaki: Conceptualization (Equal); Investigation (Equal); Resources (Supporting). CONFLICT OF INTEREST STATEMENT Shigeharu Ueki received grants and honoraria for lectures from AstraZeneca, honoraria for lectures from GlaxoSmithKline and Sanofi, and grants from Novartis, VIB, and Maruho Co. Ltd. FUNDING INFORMATION Japan Society for the Promotion of Science, Grant/Award Numbers: 20H03832, 20K08794, 21K07833, 21K08434 ACKNOWLEDGMENTS This work was funded by the Ministry of Education, Culture, Sports, Science and Technology, Japan Society for the Promotion of Science (20H03832, 20K08794, 21K07833, 21K08434). DATA AVAILABILITY STATEMENT Data available on request from the authors. ==== Refs REFERENCES 1 Chen W , Bai Y , Kong W , et al. Predictive significance of Charcot‐Leyden crystal structures for nasal polyp recurrence. Clin Transl Allergy. 2022;12 (11 ). 10.1002/clt2.12212 2 Ueki S , Melo RC , Ghiran I , Spencer LA , Dvorak AM , Weller PF . Eosinophil extracellular DNA trap cell death mediates lytic release of free secretion‐competent eosinophil granules in humans. Blood. 2013;121 (11 ):2074‐2083. 10.1182/blood-2012-05-432088 23303825 3 Ueki S , Tokunaga T , Melo RCN , et al. Charcot‐Leyden crystal formation is closely associated with eosinophil extracellular trap cell death. Blood. 2018;132 (20 ):2183‐2187. 10.1182/blood-2018-04-842260 30154112 4 Miyabe Y , Kobayashi Y , Fukuchi M , et al. Eosinophil‐mediated inflammation in the absence of eosinophilia. Asia Pac Allergy. 2021;11 (3 ):e30. 10.5415/apallergy.2021.11.e30 34386406 5 Persson EK , Verstraete K , Heyndrickx I , et al. Protein crystallization promotes type 2 immunity and is reversible by antibody treatment. Science. 2019;364 (6442 ). 10.1126/science.aaw4295 6 Tokunaga T , Sakashita M , Haruna T , et al. Novel scoring system and algorithm for classifying chronic rhinosinusitis: the JESREC Study. Allergy. 2015;70 (8 ):995‐1003. 10.1111/all.12644 25945591