Importance of lipid droplets to immunosuppression in Coxiella burnetii-infected alveolar macrophages.

Faculty Advisor

Dr. Minal Mulye, Ph.D.

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Medicine and Health Sciences


Coxiella burnetii, the known causative agent of Q fever, is an obligate intracellular bacterium capable of infecting host alveolar macrophages and residing within these cells for several years. While causing mild symptoms at initial infection, C. burnetii retains the ability to survive long-term by disseminating and causing serious complications such as culture-negative endocarditis. Previous studies in endocarditis patients demonstrated that C. burnetii suppresses the host immune response via production of prosta-glandin E2 (PGE2) and modulation of the anti-inflammatory cytokine IL-10 and proin-flammatory nitric oxide (NO). C. burnetii is also found in lipid droplet-rich foam cells suggesting the importance of host cell immune response and lipid metabolism during bacterial infection. Previous studies in our lab revealed that C. burnetii manipulates host cell lipid storage organelles, lipid droplets (LDs) via its type 4 secretion system (T4SS) which secrets effector proteins into the host cell cytoplasm to modulate cellular processes. Further, we observed that breakdown of LDs is essential for C. burnetii growth suggesting the importance of LD-derived lipids during bacterial infection. LD breakdown releases arachidonic acid, a PGE2 precursor. Since PGE2 plays an immu-nosuppressive role during C. burnetii infection, we hypothesize that LD-derived PGE2 production leads to modulation of IL-10 and NO. To assess this, we determined IL-10 and NO production enzyme iNOS gene expression in mouse alveolar macrophages by quantitative Real Time PCR (RT-qPCR). Compared to uninfected cells, iNOS gene expression decreased while IL-10 expression remained unchanged. Further we per-formed ELISA to determine IL-10 protein level and identify the contribution of LDs con-tribute IL-10 production. Compared to uninfected cells, IL-10 production in C. burnetii-infected cells remained unchanged. Surprisingly, compared to untreated cells, blocking LD formation and breakdown with specific inhibitors resulted in increased IL-10 produc-tion. This suggests that LDs play an important role in IL-10 production in C. burnetii-infected cells. However, if IL-10 contributes to immunosuppression is yet to be deter-mined. Ongoing studies are identifying the importance of LDs in NO production. Future studies will determine the changes in the overall cytokine profile in the presence/absence of LD breakdown.


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