To further examine B cells as a source of IL-1β in vivo, we examined naïve B cells (CD19 + IgD+), activated but non-GC (nGC) B cells (CD19 + IgD-GL7-CD95-), and GC B cells (CD19 + IgD-GL7 + CD95+) post A/PR8 infection (Figs 2D and S4A–S4C). Here, FAS is linked to infection.