SIGNAL-TRANSDUCTION IN THE PROTOZOAN HOST HARTMANNELLA-VERMIFORMIS UPON ATTACHMENT AND INVASION BY LEGIONELLA-MICDADEI

The intracellular pathogens Legionella micdadei and Legionella pneumop hila are the two most common Legionella species that cause Legionnaire s' disease. Intracellular replication within pulmonary cells is the ha llmark of Legionnaires' disease. In the environment, legionellae are p arasites of protozoans, and intracellular bacterial replication within protozoans plays a major role in the transmission of Legionnaires' di sease. In this study, we characterized the initial host signal transdu ction mechanisms involved during attachment to and invasion of the pro tozoan host Hartmannella vermiformis by L. micdadei. Bacterial attachm ent prior to invasion of H. vermiformis by L. micdadei is associated w ith tyrosine dephosphorylation of multiple host cell proteins, includi ng a 170-kDa protein. We have previously shown that this 170-kDa prote in is the galactose N-acetylgalactosamine (Gal/GalNAc)-inhibitable lec tin receptor that mediates attachment to and invasion of H. vermiformi s by L. pneumophila. Subsequent bacterial entry targets L. micdadei in to a phagosome that is not surrounded by the rough endoplasmic reticul um (RER), In contrast, uptake of L, pneumophila mediated by attachment to the Gal/GalNAc lectin is followed by targeting of the bacterium in to an RER-surrounded phagosome. These results indicate that despite si milarities in the L. micdadei and L. pneumophila attachment-mediated s ignal transduction mechanisms in H. vermiformis, the two bacterial spe cies are targeted into morphologically distinct phagosomes in their na tural protozoan host.