The pre-fusion antigenic changes in gB, gH, and gp150 occur independently of each other.

<p><b>(A)</b> NMuMG cells were incubated with gp150^- MuHV-4 (2h, 4°C), washed, and then either fixed immediately or first further incubated (2h, 37°C) to allow virion endocytosis. Cells were then stained with the gB-specific mAbs BN-1A7 (IgG_2a) and MG-1A12 (IgG_2a), the gH/gL-specific mAb T2C12 (IgG_2a), and the gH-only-specific mAb MG-9B10 (IgG_2a) (green). The cells were also stained for LAMP-1 (red) and with DAPI (blue). gp150^- virus showed the same gB and gH changes as wild-type. <b>(B)</b> NMuMG cells were incubated with gL^- MuHV-4 (2h, 4°C), washed, and then either fixed immediately or first further incubated (2h, 37°C) to allow virion endocytosis. Cells were then stained with the gB-specific mAbs BN-1A7 (IgG_2a) and MG-1A12 (IgG_2a) and the gp150-specific mAbs T1A1 (IgG_2a) and BH-6H2 (IgG_2b) (green). The cells were also stained for LAMP-1 (red) and with DAPI (blue). gL^- virions bound to the cell surface displayed the same gB and gp150 epitopes as wild-type, but were only poorly transported to LAMP-1⁺ late endosomes upon incubation at 37°C. Consequently, gB and gp150 largely remained in their extracellular form.