CD4 and T-cell leukemia: To determine whether Gβγ plays a role in modulating TCR-stimulated IL-2 increases, we tested the effect of gallein, a small molecule inhibitor of Gβγ signaling [22], in primary human CD4+ T cells grown for three days in conditions that promote either TH1 or TH2 differentiation and in the Jurkat human CD4+ T cell leukemia line, a well-established model system for studying T cell receptor signaling [31].