The longitudinal observational study aims to assess the impact of the microbiome especially the gut-microbiome in the emergence and course of giant cell arteritis (abbr. GCA) patients. At diagnosis and 6 month follow up we will analyze the oral, blood and gut microbiome from GCA patients and healthy controls. Thereby identified potential candidate biota will be further analyzed for possible interactions and influence on the immune system.

Inclusion Criteria:

• Diagnosis of Giant cell arteritis (only in one arm)

Exclusion Criteria:

• chronic infection (viral, fungi, bacteria) including human immunodeficiency viruses, Hepatitis B/C
• acute infection with usage of antibiotics less then 90 days before screening
• major gastro-intestinal surgery <5 years from screening
• gastro-intestinal bleeding <90 days before screening
• inflammatory bowel disease (confirmed bioptically)
• bulimia or anorexia nervosa
• adipositas (body mass index ≥ 40)
• intake of high dosage of probiotics (>10^9 colony forming units per day) <90 days before screening
• not controlled Diabetes mellitus
• Malignancy within one year (except for squamous skin - and basal skin carcinoma without metastasis, cervix carcinoma with curative surgery, Cutaneous T-cell lymphoma)
• known abuse of alcohol oder drugs.

no specific requirements, usually over 50 years