Fig. 8. Confirmation of P-IB localization to the T. gondii PVM by immunoelectron microscopy. Infected fibroblasts were labeled with rabbit anti-P-IB antibodies and 5 nm protein-A/gold particles. The reactivity of gold-labeled anti-P-IB antibodies was detected mainly around the PVM (circles), with no significant staining of the parasite being observed. Abbreviations: ER, host endoplasmic reticulum; M, host mitochondria; P, parasite; PVM, parasitophorous vacuolar membrane. The localization pattern of P-IB in the PVM of infected cells suggests a highly specific mechanism is involved in the activation of NF-B by T. gondii. Scale bars, 0.5 µm.