STAT5B and pelvic inflammatory disease: Taking advantage of the fact that human patients with PID constitute “natural models” of genetic deficiencies that provide an outstanding opportunity to elucidate still unknown features of the immune system (1, 28, 33, 34), here, we described the phenotypic and functional characteristics of the NK cells of a patient with a homozygous CD25 deficiency and compared them with NK cells from a patient with a STAT5b homozygous deficiency and HDs.