IL21 and infection: Since IL-21 shares the common receptor γ-chain with IL-4, contributing to isotype switching to IgG1 and initiation and maintenance of GC B cell responses [53–56], we examined IL-21 transcripts and found a significant repression at both D4 and D8, as compared to mock-infected mice (Fig 2A, p < 0.001), indicating impaired IgG1 responses during infection.