Figure 4.

Listeria strains expressing the listeriolysin O reveal colocalization with 2,000-kDa-sized macromolecules. Macrophages were infected with LLO⁺-GFP (A–C) for 3 hours before microinjection with 2,000-kDa Texas Red-tagged dextrans and were visualized by confocal microscopy. LLO⁺-GFP (A, yellow arrow) were readily observed within regions completely accessible to the large dextran molecules (B), thereby enabling colocalization of the two fluorescent signals (C). Macrophages infected with LLO-GFP (D, white arrow) then microinjected with 3-kDa Texas Red-tagged dextrans (E) failed to reveal signal colocalization (F).