Results obtained in mice deficient for IL-2 (Sadlack et al., 1993, 1995) or its receptor (Suzuki et al., 1995; Willerford et al., 1995), which develop extensive lymphadenopathy and die of systemic auto-immunity early after birth, extended the role of IL-2 from a “T Cell Growth Factor” (Smith et al., 1980) to “the gatekeeper of immunological tolerance”. Here, IL2 is linked to Lymphadenopathy.