Aarn is a Consultant Immunologist at University Hospitals Birmingham. He trained in Trinity College, Dublin, and moved to the UK to undertake his PhD at the University of Birmingham. After clinical training in Immunology in Nottingham, he came back to Birmingham to join the Immunology department at Birmingham Heartlands Hospital. For the last 20 years Wednesday (Immunodeficiency Clinic) has been his favourite day of the week. In addition to building the Immunology service in Birmingham, he is an active trainer and examiner in Immunology, and he has been an assessor for the UKPIN and QPIDS Immunology service accreditation schemes. The department also collaborates widely in immunodeficiency research, helping our patients contribute to new understanding of immune disorders and the development of treatments for these conditions.