This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Inositol-phosphoryl ceramide synthase 1 (Ipc1) is a fungal enzyme that modulates sphingolipid and diacylglycerol levels, and found to transcriptionally regulate a novel gene that encodes for an antiphagocytic protein (App1). App1 is a cryptococcal cytoplasmic protein that is secreted extracellularly and during cryptococcal infection in AIDS patients. Treatment with recombinant App1 in vitro significantly inhibited both attachment and ingestion of cryptococcal cells by AMs, and an ?app1 mutant strain was increasingly ingested by AMs compared to wild-type strain. App1 blocks phagocytosis of iC3b-IgM/IgG-coated erythrocytes whereas it did not inhibit attachment or/and ingestion of IgM/IgG-coated erythrocytes, suggesting that App1 acts through a complement-mediated mechanism. ?app1 mutant has no defect on virulence factors such as melanin production or capsule formation, or on growth at 30 C or 37 C compared to the wild-type strain. Importantly, by performing survival, tissue burden culture, and histopathological studies in mouse models, we find that depletion of Ipc1 and absence of App1 decreased cryptococcal virulence in an immunocompetent host. However, in an immunocompromised host deficient in T and NK cells, depletion of Ipc1 decreases virulence, whereas lack of App1 exacerbates cryptococcal infection. These studies identify App1 downstream of Ipc1 as a novel regulator of phagocytosis and virulence through a complement-mediated mechanism, and it highlights that internalization of cryptococcal cells by AMs favors the dissemination of the infection when the host cellular response is impaired. Although the development of App1 as antifungal target is unlikely (its absence exacerbates the infection in an immunodeficient mouse model), it could be developed as a prognostic marker to monitor the cryptococcal infection in AIDS patients, so that a more adequate antifungal treatment may be administered.
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