Synergy of Host Defense Mechanisms in the Lung

Johns Hopkins University, Baltimore MD

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Abstract

? DESCRIPTION (provided by applicant): This application proposes to continue our studies on the intracellular lifestyle of the human pathogenic fungus Cryptococcus neoformans, which is a major pathogen of immunosuppressed individuals such as patients with AIDS, transplant recipients, and those on immunosuppressive therapy. C. neoformans is a facultative intracellular pathogen and is dependent on its ability to survive in macrophages for its pathogenic mechanisms. Perhaps the most dramatic effect observed with C. neoformans is the phenomenon of non-lytic exocytosis whereby fungal cells are released from macrophages without lysis or apparent damage to the host cells. Non-lytic phagocytosis involves contributions from both the fungus and host cells and it must be a remarkably well choreographed process whereby the phagosomal membrane fuses with the cell membrane to disgorge the phagosomal contents into the extracellular space without host cell lysis. The phenomenon of non-lytic exocytosis has now been documented in mammalian, insect, slime mold and protozoal cells indicating remarkable specificity for different hosts, a fact suggesting that it either exploits hihly conserved eukaryotic cellular mechanisms or includes redundant mechanisms. Preliminary studies indicate that two highly conserved eukaryotic cellular systems are involved in C. neoformans non-lytic exocytosis from macrophages: autophagy and annexins. Furthermore, the requirement for fungal viability in non-lytic exocytosis events implies active modification of the cryptococcal phagosome by the fungus. Consequently, this application proposes the following three specific aims: 1. To establish the relationship between macrophage damage and CN non-lytic exocytosis; 2. To establish the mechanism by which host annexins contribute to CN non-lytic exocytosis; 3. To identify the fungal components that facilitates non-lytic exocytosis.