Herpes Simplex Virus Co-Infection-Induced Chlamydia Trachomatis Persistence Is Not Mediated by Any Known Persistence Inducer or Anti-Chlamydial Pathway

Several inducers of chlamydial persistence have been described, including interferon-γ (IFN-γ), IFN-α, IFN-β, and tumour necrosis factor-α (TNF-α) exposure, and iron, amino acid or glucose deprivation. A tissue-culture model of Chlamydia trachomatis/herpes simplex virus type-2 (HSV-2) co-infection indicates that viral co-infection stimulates the formation of persistent chlamydiae. This study was designed to ascertain whether co-infection-induced persistence is mediated by a previously characterized mechanism. Luminex assays indicate that IFN-γ, IFN-α, and TNF-α are not released from co-infected cells. Semiquantitative RT-PCR studies demonstrate that IFN-β, IFN-γ, indoleamine 2,3-dioxygenase, lymphotoxin-α and inducible nitric oxide synthase are not expressed during co-infection. These data indicate that viral-induced persistence is not stimulated by any persistence-associated cytokine. Supplementation of co-infected cells with excess amino acids, iron-saturated holotransferrin, glucose or a combination of amino acids and iron does not restore chlamydial infectivity, demonstrating that HSV-2-induced persistence is not mediated by depletion of these nutrients. Finally, inclusions within co-infected cells continue to enlarge and incorporate C6-NBD-ceramide, indicating that HSV-2 co-infection does not inhibit vesicular transport to the developing inclusion. Collectively these data demonstrate that co-infection-induced persistence is not mediated by any currently characterized persistence inducer or anti-chlamydial pathway. Previous studies indicate that HSV-2 attachment and/or entry into the host cell is sufficient for stimulating chlamydial persistence, suggesting that viral attachment and/or entry may trigger a novel host pathway which restricts chlamydial development.