725. Inhibition of Apoptosis in Respiratory Epithelial Cells Continuously Infected with Chlamydia pneumoniae (Cpn): Increased Resistance to Oxidative Stress
Session: Poster Session: Immunology/Pathogenesis
Saturday, 11 October 2003: 12:00 AM
Room: Exhibit Hall A
Background: Persistent infection with Cpn has been implicated in the pathogenesis of several chronic diseases including atherosclerosis and asthma. The mechanisms of chlamydial persistence are unclear. Previous studies have demonstrated that Chlamydia can both induce and inhibit apoptosis depending on host cell type and stage of infection. Our aim was to evaluate the effect of long-term continuous (LTC) infection with Cpn TW-183 on host cell apoptosis using a previously described in vitro model of persistent infection, which may be more relevant to infection in vivo. These LTC infected cells have been maintained for > 5 years without addition of chlamydiae, new cells, cycloheximide or centrifugation. This model has been established in A-549 and HEp-2 cells.
Methods: Acute infection of A-549 and HEp-2 cells (ATCC) was achieved by inoculation with Cpn TW-183 at an MOI 1:1. Apoptosis was induced in acute, LTC and mock-infected cells by incubating with sorbitol (1M), hydrogen peroxide (H2O2 1-10μM) and by serum withdrawal (48h). Apoptotic cells were detected by fluorescence microscopy with propidium iodide (PI), Hoechst and Annexin staining and FACS analysis with PI staining.
Results: Acute Cpn infection induced cell death (60%) after 3-4 days post infection. In contrast LTC infected cells exhibited a reduced rate of apoptosis (<5%) untreated and after incubation with sorbitol, H2O2 or serum withdrawal compared to mock-infected cells (5% background apoptosis, up to 40% apoptotic cells following induction with sorbitol).
Conclusions: Resistance of LTC infected cells to apoptosis induced by serum withdrawal and H2O2 suggests a mechanism involving oxidative stress. Induction of apoptosis in acute infection may facilitate release of Cpn from the host cell. In contrast, inhibition of apoptosis may help to protect the organism when it is in the persistent state. More studies are needed to further define the mechanism of chlamydial persistence, which could lead to a marker for identifying persistent Cpn in humans .
Patricia Roblin, MS1, Margaret Hammerschlag, MD1, Stephan Kohlhoff, MD1, Andrei Kutlin, PhD1 and  S.A. Kohlhoff, None; P.M. Roblin, None; A. Kutlin, None; M.R. Hammerschlag, None., (1)SUNY Downstate Medical Center, Brooklyn, NY


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