{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,27]],"date-time":"2026-05-27T11:57:36Z","timestamp":1779883056616,"version":"3.53.1"},"reference-count":41,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2025,10,1]],"date-time":"2025-10-01T00:00:00Z","timestamp":1759276800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["www.mdpi.com"],"crossmark-restriction":true},"short-container-title":["Life"],"abstract":"<jats:p>Background: Elevated serum IgE has been reported in severe COVID-19, suggesting that mast cell activation, allergic-like responses, and possible viral immune evasion occur. Objective: This study aimed to assess serum IgE, IgG, eosinophils, basophils, IL-10, and IL-33 in COVID-19 patients, and evaluate the infiltration of mast cells, basophils, and plasma cells in fatal cases. Methods: This retrospective study included 21 patients with severe COVID-19 or related respiratory conditions hospitalized in Plovdiv, Bulgaria (February 2020\u2013May 2022). Serum immunoglobulins were quantified via immunoassays; IL-10 and IL-33 were also measured. Lung tissues from 30 autopsies were examined histologically and immunohistochemically using CD117 (mast cells) and CD138 (plasma cells). Results: Elevated IgE (&gt;100 IU\/mL) occurred in 10\/21 patients, with two patients exhibiting levels exceeding 1000 IU\/mL. High IgE correlated with reduced eosinophils and basophils, except in post-COVID lobar pneumonia. IL-10 was significantly increased, while IL-33 was reduced in acute and long COVID. Lung histology showed the accumulation of mast cells and plasma cells (5\u201320\/field) during the diffuse alveolar damage and acute respiratory distress syndrome (ARDS) phases, but not in later fibrotic stages. Basophils are located near capillary basement membranes and the endothelium. Conclusions: SARS-CoV-2 may induce IgE-driven allergic-like mechanisms that contribute to severity. Monitoring IgE and mast cell activity may provide prognostic and therapeutic value, while elevated IgG4 could mitigate the effects of IgE.<\/jats:p>","DOI":"10.3390\/life15101538","type":"journal-article","created":{"date-parts":[[2025,10,1]],"date-time":"2025-10-01T07:58:13Z","timestamp":1759305493000},"page":"1538","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["High Free IgE and Mast Cell Activation in Long COVID: Mechanisms of Persistent Immune Dysregulation"],"prefix":"10.3390","volume":"15","author":[{"given":"Sylvia","family":"Genova","sequence":"first","affiliation":[{"name":"Department of General and Clinical Pathology, Faculty of Medicine, Medical University of Plovdiv, 4002 Plovdiv, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0411-2291","authenticated-orcid":false,"given":"Mina","family":"Pencheva","sequence":"additional","affiliation":[{"name":"Department of Medical Physics and Biophysics, Faculty of Pharmacy, Medical University of Plovdiv, 4002 Plovdiv, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3316-9916","authenticated-orcid":false,"given":"Hasan","family":"Burnusuzov","sequence":"additional","affiliation":[{"name":"Department of Medical Microbiology and Immunology, Faculty of Medicine, Medical University of Plovdiv, 4002 Plovdiv, Bulgaria"},{"name":"Research Institute, Medical University of Plovdiv, 4002 Plovdiv, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4230-3299","authenticated-orcid":false,"given":"Martina","family":"Bozhkova","sequence":"additional","affiliation":[{"name":"Department of Medical Microbiology and Immunology, Faculty of Medicine, Medical University of Plovdiv, 4002 Plovdiv, Bulgaria"},{"name":"Research Institute, Medical University of Plovdiv, 4002 Plovdiv, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Georgi","family":"Kulinski","sequence":"additional","affiliation":[{"name":"Gastroenterology Section, Second Department of Internal Medicine, Faculty of Medicine, Medical University of Plovdiv, 4002 Plovdiv, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stefka","family":"Kostyaneva","sequence":"additional","affiliation":[{"name":"Nephrology Section, Second Department of Internal Medicine, Faculty of Medicine, Medical University of Plovdiv, 4002 Plovdiv, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Eduard","family":"Tilkiyan","sequence":"additional","affiliation":[{"name":"Nephrology Section, Second Department of Internal Medicine, Faculty of Medicine, Medical University of Plovdiv, 4002 Plovdiv, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tsvetana","family":"Abadjieva","sequence":"additional","affiliation":[{"name":"Department of Dermatology and Venereology, Faculty of Medicine, Medical University of Plovdiv, 4002 Plovdiv, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,10,1]]},"reference":[{"key":"ref_1","first-page":"1495","article-title":"A Pilot Study for IgE as a Prognostic Biomarker in COVID-19","volume":"52","year":"2022","journal-title":"Intern. 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