Scientists track mysterious immune deficiency for clues

This study aims to understand a rare condition called Idiopathic CD4+ Lymphocytopenia (ICL), where people have very low levels of a key infection-fighting white blood cell for unknown reasons. Researchers will observe up to 950 participants, including patients with ICL and their family members, for 4 to 20 years to track health changes and collect samples. The goal is to learn what causes ICL, how it progresses, and why it sometimes leads to serious infections or autoimmune problems, but it does not test any new treatments.