FIG. 1.

Entry of L. monocytogenes into glial cell cultures. Glial cells were incubated with L. monocytogenes for 40 min, unbound bacteria were washed away, and the cells were resuspended in medium containing gentamicin and incubated for 2 h. The cells were fixed and stained with antibodies against cell type-specific markers (Ox42, GFAP, or Rip) and against the bacterial pathogen. The different types of glial cells are shown on the left panels. Differential immunofluorescence labeling of the bacteria was performed in order to discriminate between extracellular and intracellular bacteria, as previously described (see Material and Methods). Extracellular bacteria are indicated by thin arrows and are both green and red whereas intracellular bacteria, indicated by thick arrows, are only red. Two microglial cells are shown in panel A and a bulk of intracellular Listeria cells is shown in panel B. Astrocyte type 1, astrocyte type 2, and oligodendrocyte are shown in panels C, E, and G, respectively, and extracellular L. monocytogenes (thin arrows) and intracellular L. monocytogenes (thick arrows) are shown in panels D, F, and H. Scale bar, 10 μm.