INTERNALIN-B PROMOTES THE REPLICATION OF LISTERIA-MONOCYTOGENES IN MOUSE HEPATOCYTES

The uptake of Listeria monocytogenes by a variety of cell types in vit ro is facilitated by the protein products of the inlAB (internalin) op eron expressed by the organism, In the case of mouse hepatocytes, the extent to which inlAB expression influenced the uptake of Listeria in vitro was markedly dependent upon the ratio of bacteria to cells, At a ratio of 100:1, greater than 40-fold fewer transposon-induced inlAB m utant listeriae entered hepatocytes compared to the isogenic mild-type control; the difference was only fourfold, however, in cultures inocu lated at a 1:1 ratio. Similarly, the uptake of in-frame inlB or inlAB deletion mutants differed only fourfold from the uptake of wild-type o r inlA mutant Listeria at a 1:1 multiplicity of infection, Mutations a ffecting inlB or inlAB, on the other hand, resulted in a marked decrea se in the capacity of Lister ia to proliferate within mouse hepatocyte s in vivo and in vitro. Electron micrographs of Listeria-infected hepa tocytes demonstrated the impaired capacity of inlB mutants to escape f rom endocytic vacuoles and to enter the cytoplasm where proliferation occurs. These findings indicate that the protein product of inlB exert s a significant effect on the intracellular replication of Listeria.