The importance of the molecule can be understood by the fact that people with null CTLA4 alleles develop immunodeficiency as a form of an autosomal dominant immune dysregulation syndrome, characterised by hypogammaglobulinemia and recurrent infections with several tissues being affected, whilst CTLA4-Knockout (CTLA4-KO) mice develop fatal lymphoproliferative disease in the first weeks of life (30). The gene discussed is CTLA4; the disease is infection.