To determine whether IL-3, IL-5, and GM-CSF direct signaling to breast tumor cells is the mediator of Th2 cell immunity against breast cancer, we generated MMTV-PyMT-mCherry-Ovatg, Csf2rb−/−, Csf2rb2−/− (PyMtOvatg Csf2rbKO Csf2rb2KO) mice, which develop breast tumors lacking common β chain (Csf2rb) and IL-3 receptor class 2 subunit β (Csf2rb2) receptors. The gene discussed is IL3; the disease is breast carcinoma.