It is further noteworthy that while the mechanism of weak TCR signal failing to curtail STAT5b activity has not yet been studied in the human TCR signaling defects, gain-of-function missense mutations in STAT5b, and JAK1—which activates STAT5b—are associated with syndromes characterized by profound early onset dermatitis and eosinophilia (75, 76). Here, STAT5B is linked to Increased total eosinophil count.