One of the main potential causes of these failures of BP therapy response is the development of Anti-drug Anti-body (ADAb) in some patients. ADAb may decrease the efficacy of BPs by neutralizing them or modifying their clearance and they may be associated with BP-specific hypersensitivity reactions. The prediction, prevention and cure of anti-drug (AD) immunization are thus major goals in BP development. This prospective study (ABI-RA) will assess the occurrence of ADAb using standardized and validated assay(s) and also cellular, genetic and molecular parameters in RA/JIA patients treated with adalimumab, etanercept, infliximab and rituximab or tocilizumab, to address the mechanism of immunogenicity. Patient-related factors that might predispose an individual to an immune response will be taken into account: underlying disease, genetic background, immune status, including immunomodulating therapy and dosing schedule.