The Fas-mediated apoptosis assay: From concept to clinical application.

Abnormal lymphocyte homeostasis underly several Inborn Errors of Immunity (IEoI). In vitro assessment of lymphocyte homeostasis is achieved by specific apoptosis assays reflective of specific homeostasis programs and pathways that are mediated through specific proteins. This review discusses those programs, pathways and proteins and describes the development and use of the in vitro Fas-mediated apoptosis assay, as it relates to the IEoI Autoimmune Lymphoproliferative Syndrome (ALPS) and describes other disorders of lymphocyte homeostasis in the context of other forms of in vitro apoptosis assessment.