TBX21 and bacterial infectious disease: This primed, polyfunctional phenotype could be explained by the fact that all three subpopulations expressed Tbet, a transcription factor encoded by the TBX21 gene, which is known to accumulate in CLL (23), and is associated with increased production of the pro-inflammatory cytokine IFNγ (24–27), increased expression of the IL-2 receptor (26), and protection against viral and bacterial infections in multiple murine models (24, 28, 29).