The hypothesis of the study is that the presence of (subclinical) gut inflammation at baseline in patients with early active axial spondyloarthritis predisposes to a more severe disease defined as more need to use anti-tumor necrosis factor α therapy and a shorter time to relapse after stopping anti-tumor necrosis factor α therapy after obtaining sustained clinical remission. Overall, the investigators hypothesize that subclinical gut inflammation is an important predictor in therapy response and outcome. These data could provide better insights into the complex interactions between gut and joint inflammation and guide the physicians in the therapeutic approach.

Inclusion Criteria:

• Subject must have a diagnosis of axSpA and classified according to ASAS criteria.
• Subject has at least 3 months and maximum 1 year (almost) daily chronic back pain.
• Subject has an active disease defined as a positive MRI (according to ASAS definition) or elevated CRP (in patients who are HLA-B27+) and an ASDAS score > 2.1 (at least high disease activity).

Exclusion Criteria:

• Full anti-inflammatory dose of NSAIDs for more than 4 weeks for the duration of the axSpA symptoms.
• Prior exposure to any biologic therapy with a potential therapeutic impact on SpA, including anti-TNF therapy.
• Exposure to disease-modifying drugs (DMARDSs; i.e. methotrexate and sulfasalazine) in the last 3 months before the ileocolonoscopy.
• Exposure to systemic corticosteroid treatment in the last 14 days before the ileocolonoscopy.
• Infection(s) requiring treatment with intravenous antibiotics/antivirals/antifungals within 30 days prior to the baseline visit or oral antibiotics/antivirals/antifungals within 14 days prior to the baseline visit.
• Have a known hypersensitivity to human immunoglobulin proteins or other components of golimumab.
• History of central nervous system (CNS) demyelinating disease or neurologic symptoms suggestive of CNS demyelinating disease.
• History of listeriosis, histoplasmosis, chronic of active hepatitis B infection, hepatitis C infection, human immunodeficiency virus (HIV) infection, immunodeficiency syndrome, chronic recurring infections or active tuberculosis.
• Have a history of, or concurrent, chronic heart failure, including medically controlled, asymptomatic congestive heart failure.
• Evidence of dysplasia or history of malignancy (including lymphoma and leukemia) other than a successfully treated non-metastatic cutaneous squamous cell or basal cell carcinoma or localized carcinoma in situ of the cervix.
• Have received, or are expected to receive, any live virus or bacterial vaccination within 3 months prior to the first administration of study agent, during the trial, or within 6 months after the last administration of study agent.
• Positive pregnancy test at screening.
• Female subjects who are breast-feeding or considering becoming pregnant during the study.
• Female subjects who do not use contraceptives.
• History of clinically significant drug or alcohol abuse in the last 12 months.
• Clinically significant abnormal screening laboratory results as evaluated by the investigator.
• Positive rheumatoid factor (RF) or anti-cyclic citrullinated peptide (anti-CCP) antibody at screening if the titers are crossing 3 times the upper limit of the normal.
• Subject with diagnosis and current symptoms of fibromyalgia.
• Any medical or psychological condition that, in the opinion of the investigator, could jeopardize or compromise the subject's ability to participate in this study.

Patients included in the trial and for whom the treatment protocol was initiated.

Adverse events data was collected between the first dose administration of trial medication and the last trial related activity (through study completion, between 24 weeks and 52 weeks). Medical events that occurred between signing of the Informed Consent and the first intake of trial medication were documented as medical and surgical history section and concomitant diseases.

All adverse events and serious adverse events were recorded in the patient's file and in the Case Report Form. Adverse Events were defined as any untoward medical occurrence in a patient administered a pharmaceutical product and which does not necessarily have a causal relationship with this treatment.

The trial included 64 of initially anticipated 147 patients, which impacts downstream analyses which were powered for a larger group.

The baseline prevalence of gut inflammation in the studied patient population was lower than anticipated. Therefore primary objective of the study (to evaluate whether there is a higher need of anti-TNFα treatment in patients with gut inflammation compared to those without) could not be adressed.