{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T14:48:19Z","timestamp":1785422899157,"version":"3.56.0"},"reference-count":38,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2026,7,20]],"date-time":"2026-07-20T00:00:00Z","timestamp":1784505600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000780","name":"European Union","doi-asserted-by":"publisher","award":["BG-RRP-2.004-0008-C01"],"award-info":[{"award-number":["BG-RRP-2.004-0008-C01"]}],"id":[{"id":"10.13039\/501100000780","id-type":"DOI","asserted-by":"publisher"}]},{"award":["BG-RRP-2.004-0008-C01"],"award-info":[{"award-number":["BG-RRP-2.004-0008-C01"]}],"id":[{"id":"https:\/\/ror.org\/019w4f821","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Antibodies"],"abstract":"<jats:p>Background\/Objectives: The autoimmune disorder Systemic Lupus Erythematosus (SLE) is characterized by increased titers of autoantibodies with different specificities against autoantigens, including the complement proteins C1q, C3 and Factor H. SLE is characterized by chronic inflammation and tissue damage due to the secretion of pro-inflammatory molecules and a tissue deposition of immune complexes formed by autoantibodies and their target antigens. The inflammatory process in SLE is maintained by the phospholipase A2 (PLA2) enzymes generating pro-inflammatory lipid mediators. Hereditary and environmental factors trigger SLE, with increased genetic heritability in first-degree relatives of SLE patients. Methods: A cohort of 48 healthy FDRs of SLE patients was analyzed with the ELISA method for the presence of antibodies to complement proteins C1q, C3 and Factor H, with a focus on detecting autoepitopes both on immobilized and soluble C1q and its globular fragments ghA, ghB and ghC. The total serum PLA2 activity of FDRs was measured using the chromogenic substrate 4-nitro-3-octanoyloxy-benzoic acid (NOBA). Results: Only C1q, and specifically its globular domains in both an immobilized and soluble state, was targeted by antibodies in the healthy FDRs similarly to the pattern established in SLE patients. In contrast, C3 and Factor H which are known autoantigens in SLE were not found as targets for the antibodies in the analyzed FDRs. Some of the FDRs showed increased serum PLA2 activity, which correlated weakly with anti-C1q antibodies. Conclusions: C1q and its globular domains are estimated as autoantigenic molecules for binding in the analyzed FDRs of SLE patients.<\/jats:p>","DOI":"10.3390\/antib15040062","type":"journal-article","created":{"date-parts":[[2026,7,20]],"date-time":"2026-07-20T13:18:31Z","timestamp":1784553511000},"page":"62","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Sera of Healthy First-Degree Relatives of SLE Patients Contain Autoantibodies to Globular Domains of C1q"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-4375-5115","authenticated-orcid":false,"given":"Ginka","family":"Cholakova","sequence":"first","affiliation":[{"name":"Faculty of Biology, Department of Biochemistry, Sofia University, 1164 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0004-0752-2159","authenticated-orcid":false,"given":"Alexandra","family":"Atanasova","sequence":"additional","affiliation":[{"name":"Faculty of Biology, Department of Biochemistry, Sofia University, 1164 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alexandra","family":"Kapogianni","sequence":"additional","affiliation":[{"name":"Faculty of Biology, Department of Biochemistry, Sofia University, 1164 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dobroslav","family":"Kyurkchiev","sequence":"additional","affiliation":[{"name":"Laboratory of Clinical Immunology, University Hospital \u201cSt. Ivan Rilski\u201d, Department of Clinical Immunology, Medical University of Sofia, 1431 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5005-4259","authenticated-orcid":false,"given":"Bogdan","family":"Penev","sequence":"additional","affiliation":[{"name":"Rheumatology Department, Sofiamed University Hospital, 1336 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3308-4154","authenticated-orcid":false,"given":"Ivanka","family":"Tsacheva","sequence":"additional","affiliation":[{"name":"Faculty of Biology, Department of Biochemistry, Sofia University, 1164 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"102","DOI":"10.1038\/s41392-025-02168-0","article-title":"Systemic lupus erythematosus: Updated insights on the pathogenesis, diagnosis, prevention and therapeutics","volume":"10","author":"Dai","year":"2025","journal-title":"Signal Transduct. 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