Author(s): Iman Ellahie
Mentor(s): Joseph M Bednarek, Jessica Brown
Institution U of U
BACKGROUND: Cryptococcus neoformans is a ubiquitous environmental pathogen that causes severe infection in immunocompromised individuals, specifically those with low CD4+ T cell counts. HIV/AIDS is a disease defined by CD4+ T cell deficiency and is thus a primary risk factor for cryptococcal infection. Under immunosuppression, fungal particles in the lungs escape to the bloodstream and disseminate throughout the body, ultimately invading the brain and causing fatal meningoencephalitis. CD4+ T cells play an important role in mounting the inflammatory immune response necessary to resolve cryptococcal infections. Despite their importance, it remains unclear how CD4+ T cell deficiency alters the spread of C. neoformans in the bloodstream and whether infection impacts immune cells in the blood. OBJECTIVE: With this study, we will identify whether C. neoformans infection changes the profile of immune cells in the bloodstream of wild-type (WT) and CD4+ T cell deficient (CD4KO) mice. Notably, CD4+ T cells are involved in the signaling of several key cell types, including B cells, monocytes, and macrophages. Therefore, we expect CD4KO mice will exhibit an altered immune response relative to the WT controls. METHODS: Fungal burden and blood dissemination are analyzed using a murine model of infection, selection plating, and flow cytometry. Cell-type specific antibodies are used to determine the size, granularity, and protein expression of immune cells with a Cytoflex flow cytometer. These antibodies allow us to characterize both lymphocytes (CD4+ T cells, CD8+ T cells, B cells) and granulocytes (neutrophils, monocytes, eosinophils, basophils). RESULTS: CD4KO mice succumb to infection faster than WT mice, beginning at 6 days post infection compared to 18 days. The appearance of fungi in the bloodstream is also faster in CD4KO mice, beginning 12 days post infection. Lastly, there is a significant increase in the blood neutrophil population of CD4KO mice relative to WT. CONCLUSIONS: This work introduces a physiologically relevant model for studying the role of CD4+ T cell deficiency in cryptococcal infections. CD4KO mice appear to compensate for their deficiency with increased neutrophils during cryptococcal infection. More work is necessary to determine whether the increase in neutrophils plays a deleterious role or is simply a compensatory mechanism for CD4+ T cell deficiency and monocyte/macrophage dysfunction. This work signals a new focus for understanding the mechanisms that underlie C. neoformans infection and will allow us to determine why CD4+ T cell deficient patients are susceptible to these deadly infections.