Applications of flow cytometry for the study of primary immune deficiencies

PURPOSE OF REVIEWThis review focuses on the current applications of flow cytometry for the diagnosis and evaluation of primary immune deficiencies (PIDs). RECENT FINDINGSThe immunophenotypic evaluation of selected PIDs provides diagnostic clues as well as information useful to classify patients and predict clinical outcome. In addition, the evaluation of intracellular proteins associated with selected PIDs has evolved as a useful diagnostic screening method. Finally, functional flow cytometry can now help to clarify possible sites of genetic defects associated with specific PIDs. SUMMARYThe range of PIDs in which flow cytometry has proven to be useful from a clinical and diagnostic purpose has significantly expanded. This now includes not only patients presenting with clinical histories consistent with classical antibody deficiencies and severe combined immune deficiency, but also patients with more limited infectious histories. Included among these are patients with genetic defects associated with Mendelian susceptibility to mycobacterial disease focusing the evaluation on specific surface protein expression and cell function analysis. In addition, flow cytometry appears to provide a useful screening approach to evaluate for possible toll-like receptor-pathway defects. Furthermore, immunophenotyping and intracellular flow cytometry have proven to be valuable discriminators in the evaluation of patients with immune dysregulation syndromes including immune dysregulation, polyendocrinopathy, enteropathy, X-linked, and autoimmune lymphoproliferative syndrome. Finally, flow cytometry has been shown to be useful to screen patients with possible X-linked lymphoproliferative syndrome and familial hemophagocytic lymphohistiocytosis.