IL33 and infection: Importantly, mock-infected Il1rl1–/–mice did not show decreased Iba1+ cell number, indicating no baseline effect of IL-33 on promoting microglia number (S4A and S4B Fig) Despite its reported role in synaptic stripping by activated microglia in diverse CNS pathologies [42], complement deposition of C1q protein at 7DPI was not affected by the absence of IL-33 during infection (S4C and S4D Fig).