Haemophilia A is a hereditary bleeding disorder linked to the X chromosome characterized by a deficiency or defect in the coagulation factor VIII (FVIII). Individuals with this coagulopathy require constant infusions of FVIII to maintain their physical integrity and haemostasis. During treatment, some patients develop an immune response that produces antibodies to FVIII, also called inhibitors, affecting the pro-coagulant activity of this protein. Despite the clinical relevance of FVIII inhibitors, the immune mechanisms that lead to their production are not known. This study investigated the immunological cytokine profile using plasma from HA patients which were either positive or negative for FVIII inhibitors and from healthy individuals. The results showed that healthy individuals and HA patients that do not develop FVIII inhibitors have a mixed immune response profile with high secretion of IFN-γ, TNF-α IL-2 and IL-5. In contrast, HA patients with FVIII inhibitors exhibited an anti-inflammatory/regulatory immune response characterized by low levels of all measured cytokines except for IL-4 and IL-10. This profile may be related to the development and maintenance of the FVIII inhibitors. By comparing the cytokine profiles of the three different groups we have established a model explaining the immune activation resulting in the production of FVIII inhibitors in haemophilia A patients.

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