Flow Cytometry Assays in Primary Immunodeficiency Diseases.

Inborn errors of immunity are the cause of the primary immunodeficiency diseases, an extremely diverse group of genetic defects that are inherited in Mendelian fashion and result in the impairment of development and/or function of key components of the immune system. Since the last publication of this chapter in 2011, there have been approximately 100 new primary immunodeficiency diseases officially classified by the "Expert Committee for Primary Immunodeficiency" who met in 2015 and the numbers will continue to rise with the continued evolution and widespread adoption of genomic technologies. The ultimate diagnostic modality involves the identification of a mutation in a gene whose product is known to be involved in immunity. DNA sequencing is however still a rather time-consuming technology. Flow cytometry applications have evolved that are rapid, specific, and relatively inexpensive to screen for abnormalities associated with primary immunodeficiency diseases. The numerous flow cytometry procedures that have been developed to detect abnormalities in peripheral blood cells of primary immunodeficiency patients can barely be covered in an entire book, let alone one chapter. Instead of attempting to cover each disease with a specific assay or test, we will review four procedures each covering one of the three following broad forms of immune abnormalities observed in primary immunodeficiency, i.e., immune subset abnormalities, immune marker abnormalities, and immune function abnormalities.