The D/P-vaccinated/bi mice exhibited a larger expansion of total splenic cells (S1 Table) and T cells than was noted in the D/P-vaccinated mice in response to challenge infection, as was evidenced by a significantly higher (1.6–2.8-fold, p<0.05–0.01) frequency of proliferating and non-proliferating IFNγ+, TNFα+, and IFNγ+TNFα+ CD4+ and CD8+ T cells (compare Fig 5 with Fig 3). Here, CD4 is linked to infection.