PRF1 and infection: At a functional level, the frequencies of IFNγ- and PRF1-expressing CD4+Tem subsets were similarly increased (27%–51%) in infected and vaccinated/infected (vs. control) groups; while pregnant mice exhibited 22%–108% higher frequencies of IFNγ+, PRF1+, and GZB+CD4+Tem cells when they were vaccinated before challenge infection (Fig. 3f–h, p < 0.01–0.001).