TBX21 encodes the Th1-lineage defining transcription factor T-bet, which we found is upregulated in B cells of malaria-exposed children (n = 15; S2 Table) relative to healthy U.S adults (n = 10) in a bi-modal distribution with approximately 18% of CD19+ B cells expressing intermediate levels of T-bet (T-betint) and 8% expressing high levels of T-bet (T-bethi) (Fig 2A). This evidence concerns the gene TBX21 and malaria.