CCR2 and infection: Interestingly, CCR2-positive cells that also express the microglia marker Iba1 were detected in brain sections of the olfactory bulb (not shown) and the medulla of WT, CCR2-/-→WT and WT→CCR2-/- mice on days 6 (S1 Fig) and 8 (not shown) post-infection (p.i.)whereas no signal was detected in CCR2-/- group.