Study of the C5a/C5aR1 Axis in IgG4-associated Disease: a Potential Therapeutic Target

Inclusion Criteria for patients suffering from IG4-related disease and patients in remission : * age \> 18 * diagnosis of IgG4-associated disease according to ACR/EULAR 2019 classification criteria (4,5) with a score ≥20. * disease activity score (IgG4-RD Responder Index) ≥2 in at least one affected organ Exclusion Criteria for patients suffering from IG4-related disease and patients in remission : * presence of a differential diagnosis ("IgG4-RD mimicker") or exclusion criterion according to ACR/EULAR 2019 classification criteria (4,5). * systemic corticosteroid treatment ≥5 mg/day ongoing or \< 1 month ; Study C5-MAG4\_RCAPHM21\_0433 Protocol Version 1.1 of 16/01/2024 Page 15 of 41 * immunosuppressive therapy ongoing or \< 3 months ; * current biotherapy treatment or \< 6 months; * absence of signed informed consent; * absence of affiliation to a Social Security scheme. * patient participating in an ongoing therapeutic trial ; * any condition which, in the opinion of the investigator, could influence the results of the study. Inclusion criteria for healthy volunteers : \- age \> 18 Exclusion criteria for healthy volunteers : * infectious episode (temperature \>38°C, flu-like signs) in the 30 days prior to inclusion; * known inflammatory (including IG4-related disease) or autoimmune pathology; * treatment with corticosteroids in progress or taken in the month prior to sampling, or immunosuppressants in progress or taken in the 3 months prior to sampling, or biotherapy in the 6 months prior to sampling; * absence of signed informed consent; * absence of affiliation to a Social Security scheme; * persons taking part in an ongoing therapeutic trial; * any condition which, in the opinion of the investigator, could influence the results of the study.