In the present study, we show that lymphopenia-insensitive OT-II cells expand massively in IFN-γ receptor (IFN-γR)-deficient Rag−/− (RagγRko) mice, a phenomenon that is not observed in IFN-γ-deficient Rag−/− (Ragγko) mice. This evidence concerns the gene IFNG and lymphopenia.