**4.2 Functional analysis studying STAT phosphorylation**

Signal transducer and activator of transcription (STAT) control cellular activation processes after cell activation through cytokines. All STAT molecules are phosphorylated by receptor-associated kinases, that causes activation, by forming homo- or heterodimers and finally translocate to nucleus to function as transcription factors [37]. The study of the different STATs by flow cytometry is of great interest not only of STAT deficiencies (STAT1, STAT3 or STAT5 deficiencies) but also to study the proper
