Chlamydophila pneumoniae in human immortal Jurkat cells and primary lymphocytes uncontrolled by interferon-γ

Chlamydia trachomatis L2/434/Bu Favors Hypoxia for its Growth in Human Lymphoid Jurkat Cells While Maintaining Production of Proinflammatory Cytokines

The role of lymphocytes as a cornerstone of the inflammatory response in the invasive pathogenesis of Chlamydia trachomatis (Ct) LGV (L1-3) infection is unclear. Therefore, we assessed whether the adaptation of CtL2 to immortal lymphoid Jurkat cells under hypoxic conditions occurred through proinflammatory cytokine profile modification. The quantities of inclusion-forming units with chlamydial 16S rDNA confirmed that CtL2 grew well under hypoxic rather than normoxic conditions in the cells. Confocal microscopic imaging and transmission electron microscopy revealed the presence of bacterial progeny in the inclusions and showed that the inclusions were larger under hypoxic rather than normoxic conditions; this was supported by the results of 3D image construction. Furthermore, PCR-based analysis of proinflammatory cytokines revealed that the gene expression levels under hypoxic conditions were significantly higher than those under normoxic conditions. In particular, the expression of two genes (CXCL8 and CXCR3) was significantly diminished under normoxic conditions. Taken together, the results indicated that hypoxia promoted CtL2 growth in Jurkat cells while maintaining the levels of proinflammatory cytokines. Thus, Ct LGV infection in lymphocytes under hypoxic conditions might be crucial to a complete understanding of the invasive pathogenesis.

[Advances in application of Jurkat cell model in research on infectious diseases]

Infectious diseases can be caused by multiple pathogens, which can produce specific immune response in human body. The immune response produced by T cells is cellular immunity, which plays an important role in the anti-infection process of human body, and can participate in immunological protection and cause immunopathology. The outcome of various infectious diseases is closely related to cellular immune function, especially the function of T cells. Jurkat cells belong to the human acute T lymphocyte leukemia cell line. Jurkat cell model can simulate the function T lymphocytes, so it is widely used in the in vitro studies of T cell signal transduction, cytokines, and receptor expression, and can provide reference and guidance for the treatment of various infectious diseases and the research on their pathogenesis. The Jurkat cell model has been widely used in the in vitro studies of viral diseases and atypical pathogens, but parasitic infection studies using the Jurkat cell model are still rare. This article reviews advances in the application of Jurkat cell model in the research on infectious diseases.

Impact of capsaicin, an active component of chili pepper, on pathogenic chlamydial growth (Chlamydia trachomatis and Chlamydia pneumoniae) in immortal human epithelial HeLa cells

Chlamydia trachomatis is the leading cause of sexually transmitted infections worldwide. Capsaicin, a component of chili pepper, which can stimulate actin remodeling via capsaicin receptor TRPV1 (transient receptor potential vanilloid 1) and anti-inflammatory effects via PPARγ (peroxisome proliferator-activated receptor-γ) and LXRα (liver X receptor α), is a potential candidate to control chlamydial growth in host cells. We examined whether capsaicin could inhibit C. trachomatis growth in immortal human epithelial HeLa cells. Inclusion forming unit and quantitative PCR assays showed that capsaicin significantly inhibited bacterial growth in cells in a dose-dependent manner, even in the presence of cycloheximide, a eukaryotic protein synthesis inhibitor. Confocal microscopic and transmission electron microscopic observations revealed an obvious decrease in bacterial numbers to inclusions bodies formed in the cells. Although capsaicin can stimulate the apoptosis of cells, no increase in cleaved PARP (poly (ADP-ribose) polymerase), an apoptotic indicator, was observed at a working concentration. All of the drugs tested (capsazepine, a TRPV1 antagonist; 5CPPSS-50, an LXRα inhibitor; and T0070907, a PPARγ inhibitor) had no effect on chlamydial inhibition in the presence of capsaicin. In addition, we also confirmed that capsaicin inhibited Chlamydia pneumoniae growth, indicating a phenomena not specific to C. trachomatis. Thus, we conclude that capsaicin can block chlamydial growth without the requirement of host cell protein synthesis, but by another, yet to be defined, mechanism.

Synergistic Costimulatory Effect of Chlamydia pneumoniae with Carbon Nanoparticles on NLRP3 Inflammasome-Mediated Interleukin-1β Secretion in Macrophages

The obligate intracellular bacterium Chlamydia pneumoniae is not only a causative agent of community-acquired pneumonia but is also associated with a more serious chronic disease, asthma, which might be exacerbated by air pollution containing carbon nanoparticles. Although a detailed mechanism of exacerbation remains unknown, the proinflammatory cytokine interleukin-1β (IL-1β) is a critical player in the pathogenesis of asthma. C. pneumoniae induces IL-1β in macrophages via NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome activation and Toll-like receptor 2/4 (TLR2/4) stimulation. Carbon nanoparticles, such as carbon nanotubes (CNTs), can also evoke the NLRP3 inflammasome to trigger IL-1β secretion from lipopolysaccharide-primed macrophages. This study assessed whether costimulation of C. pneumoniae with CNTs synergistically enhanced IL-1β secretion from macrophages, and determined the molecular mechanism involved. Enhanced IL-1β secretion from C. pneumoniae-infected macrophages by CNTs was dose and time dependent. Transmission electron microscopy revealed that C. pneumoniae and CNTs were engulfed concurrently by macrophages. Inhibitors of actin polymerization or caspase-1, a component of the inflammasome, significantly blocked IL-1β secretion. Gene silencing using small interfering RNA (siRNA) targeting the NLRP3 gene also abolished IL-1β secretion. Other inhibitors (K(+) efflux inhibitor, cathepsin B inhibitor, and reactive oxygen species-generating inhibitor) also blocked IL-1β secretion. Taken together, these findings demonstrated that CNTs synergistically enhanced IL-1β secretion from C. pneumoniae-infected macrophages via the NLRP3 inflammasome and caspase-1 activation, providing novel insight into our understanding of how C. pneumoniae infection can exacerbate asthma.

Human Chlamydia pneumoniae isolates demonstrate ability to recover infectivity following penicillin treatment whereas animal isolates do not

Chlamydia pneumoniae strains have recently been demonstrated to have substantially different capacities to enter and recover from IFN-γ-induced persistence, depending on whether they are from human or animal host sources. Here, we examined the ability of two human and two animal strains to enter and be rescued from penicillin-induced persistence. The ability to form inclusions after the addition of penicillin was much reduced in the two animal isolates (koala LPCoLN, bandicoot B21) compared to the two human isolates (respiratory AR39 and heart A03). The penicillin treatment resulted in a dose-dependent loss of infectious progeny for all isolates, with the human strains failing to produce infectious progeny at lower doses of penicillin than the animal strains. The most remarkable finding however was the contrasting ability of the isolates to recover infectious progeny production after rescue by removal of the penicillin (at 72 h) and continued culture. The animal isolates both showed virtually no recovery from the penicillin treatment conditions. In contrast, the human isolates showed a significant ability to recovery infectivity, with the heart isolate (A03) showing the most marked recovery. Combined, these data further support the hypothesis that the ability to establish and recover from persistence appears to be enhanced in human C. pneumoniae strains compared to animal strains.

Chlamydia pneumoniae effector chlamydial outer protein N sequesters fructose bisphosphate aldolase A, providing a benefit to bacterial growth

Background

Pathogenic chlamydiae are obligate intracellular pathogens and have adapted successfully to human cells, causing sexually transmitted diseases or pneumonia. Chlamydial outer protein N (CopN) is likely a critical effector protein secreted by the type III secretion system in chlamydiae, which manipulates host cells. However, the mechanisms of its action remain to be clarified. In this work, we aimed to identify previously unidentified CopN effector target in host cells.

Results

We first performed a pull-down assay with recombinant glutathione S-transferase (GST) fusion CopN proteins (GST–CpCopN: Chlamydia pneumoniae TW183, GST–CtCopN: Chlamydia trachomatis D/UW-3/CX) as “bait” and soluble lysates obtained from human immortal epithelial HEp-2 cells as “prey”, followed by SDS-PAGE with mass spectroscopy (MS). We found that a host cell protein specifically bound to GST–CpCopN, but not GST–CtCopN. MS revealed the host protein to be fructose bisphosphate aldolase A (aldolase A), which plays a key role in glycolytic metabolism. We also confirmed the role of aldolase A in chlamydia-infected HEp-2 cells by using two distinct experiments for gene knockdown with an siRNA specific to aldolase A transcripts, and for assessment of glycolytic enzyme gene expression levels. As a result, both the numbers of chlamydial inclusion-forming units and RpoD transcripts were increased in the chlamydia-infected aldolase A knockdown cells, as compared with the wild-type HEp-2 cells. Meanwhile, chlamydial infection tended to enhance expression of aldolase A.

Conclusions

We discovered that one of the C. pneumoniae CopN targets is the glycolytic enzyme aldolase A. Sequestering aldolase A may be beneficial to bacterial growth in infected host cells.