*4.2.2 STAT3 phosphorylation for the diagnosis of Hiper IgE Syndrome (HIES)*

Hiper IgE Syndrome (HIES) is a PID defined as an association of atopy in a context of very high serum IgE levels, characteristic bacterial and fungal diseases, low-level clinical and biological inflammation, and various non-hematopoietic developmental manifestations. Somewhat arbitrarily, three disorders were successively put forward as the underlying cause of HIES: autosomal dominant (AD) STAT3 deficiency, the only disorder corresponding to the original definition of HIES, and autosomal recessive (AR) DOCK8 and PGM3 deficiencies, in which atopy and high serum IgE levels occur in a context of manifestations not seen in patients with typical HIES. Indeed, these three disorders disrupt different molecular pathways, affect different cell types, and underlie different clinical phenotypes [44].

Phenotype tests discussed in previous chapters, demonstrating low number of Th17 lymphocytes, may guide in-depth study of a defect in STAT3 signaling. These are the analysis of the ability to produce IL-17 by stimulation with PMA and ionomicin, adding a Golgi Plug such as Brefeldin and subsequent intracellular staining against IL17. And the STAT3 phosphorylation test in lymphocytes. Whole blood is stimulated with IL-6 and/or IL-21 and intracellular staining is performed to evaluate STAT3 phosphorylation. Different conditions are needed, such as: not stimulated, stimulated, and both with STAT3 antibodies or with an isotype control to have internal controls. Phosphorylation is clearly decreased in a patient with STAT3 deficiency compared to a healthy control [45, 46].

See STAT phosphorylation staining protocol in Section 4.2.
