Infliximab is the active ingredient in a drug currently sold by the trade names Remicade, Remsima and Inflectra. Infliximab neutralizes tumor necrosis factor (TNF) α, a chemical messenger (cytokine) in the immune system, and belongs to a class of drugs called "TNF inhibitors". 8-55% of patients receiving infliximab have an infusion reaction. Infusion reactions are unintended reactions that occur during infusion of the drug and up to 14 days after. The incidence varies widely in different studies and seems difficult to determine due to variations in reporting of reactions, different definitions of reactions and retrospective data collection. The aim of this study is to estimate the incidence of infusion related reactions and investigate risk factors and immunological mechanisms of infusion reactions to infliximab in patients with a chronic inflammatory disease.