Legionella pneumophila Is Internalized by a Macropinocytotic Uptake Pathway Controlled by the Dot/Icm System and the Mouse Lgn1 Locus✪

Abstract

The products of the Legionella pneumophila dot/icm genes enable the bacterium to replicate within a macrophage vacuole. This study demonstrates that the Dot/Icm machinery promotes macropinocytotic uptake of L. pneumophila into mouse macrophages. In mouse strains harboring a permissive Lgn1 allele, L. pneumophila promoted formation of vacuoles that were morphologically similar to macropinosomes and dependent on the presence of an intact Dot/Icm system. Macropinosome formation appeared to occur during, rather than after, the closure of the plasma membrane about the bacterium, since a fluid-phase marker preloaded into the macrophage endocytic path failed to label the bacterium-laden macropinosome. The resulting macropinosomes were rich in GM1 gangliosides and glycosylphosphatidylinositol-linked proteins. The Lgn1 allele restrictive for L. pneumophila intracellular replication prevented dot/icm-dependent macropinocytosis, with the result that phagosomes bearing the microorganism were targeted into the endocytic network. Analysis of macrophages from recombinant inbred mouse strains support the model that macropinocytotic uptake is controlled by the Lgn1 locus. These results indicate that the products of the dot/icm genes and Lgn1 are involved in controlling an internalization route initiated at the time of bacterial contact with the plasma membrane.

The amoebae plate test implicates a paralogue of lpxB in the interaction of Legionella pneumophila with Acanthamoeba castellanii

“…The Icm/Dot secretion system determines the initial contact of L. pneumophila with host cells and phagosome biogenesis (Hilbi et al, 2001;Watarai et al, 2001), is required to evade immediate endocytic maturation (Roy et al, 1998;Wiater et al, 1998) and governs subsequent formation of the ER-derived, replicative vacuole (reviewed by Nagai & Roy, 2003). Once L. pneumophila resides in this nutritionally rich compartment, the vacuole may acidify (Sturgill-Koszycki & Swanson, 2000), and bacterial replication apparently proceeds without requiring a functional Icm/Dot transporter (Coers et al, 1999).…”

Comparative assessment of virulence traits in Legionella spp.

“…The dot/icm loci are composed of 24 genes that are involved in the assembly of a type IV secretion apparatus that is central to pathogenesis. The dot/icm loci are essential for enhancement of phagocytosis by human-derived cells (Hilbi et al, 2001), macropinocytic uptake by A/J mice-derived macrophages (Watarai et al, 2001), evasion of lysosomal fusion and intracellular replication (Segal et al, 1998;Vogel et al, 1998), induction of apoptosis (Zink et al, 2002), and pore-formationmediated lysis of the host cell and bacterial egress upon termination of intracellular replication (Alli et al, 2000;Molmeret et al, 2002b). Biphasic killing of mammalian cells by L. pneumophila (Alli et al, 2000;Gao & Abu Kwaik, 1999b) has been proposed in which apoptosis is first initiated, followed by a temporal induction of necrosis and lysis of the host upon growth transition into the postexponential phase (Alli et al, 2000;Byrne & Swanson, 1998;Kirby et al, 1998).…”

Autophagy and Inflammatory Cell Death, Partners of Innate Immunity

“…[7][8][9] When ingested by resistant Naip5 + C57Bl/6 macrophages, single L. pneumophila can establish specialized replication vacuoles, but within hours their multiplication grinds to a halt. 10,11 As compared to permissive naip5 mutant A/J cells, resistant Naip5 + macrophages exhibit rapid maturation of autophagosomes, whether induced by amino acid depletion, rapamycin, or L. pneumophila. 12 Furthermore, Naip5 + macrophages are more sensitive to pathogen-induced death.…”