Chlamydia pneumoniae infection suppresses Staphylococcus enterotoxin B-induced proliferation associated with down-expression of CD25 in lymphocytes

Jurkat cell proliferation is suppressed by Chlamydia (Chlamydophila) pneumoniae infection accompanied with attenuation of phosphorylation at Thr389 of host cellular p70S6K

Chlamydia (Chlamydophila) pneumoniae infects T lymphocytes and multiplies within them. Our previous studies have indicated that C. pneumoniae infection suppresses proliferation of peripheral blood mononuclear cells stimulated with Staphylococcus-enterotoxin B; however, the mechanism of suppression was unclear. In this study, we explored the molecular mechanism involved in C. pneumoniae infection by using human acute T cell leukemia cell line, Jurkat E6-1. Proliferation of Jurkat cells was suppressed in an m.o.i.-dependent manner by C. pneumoniae infection. The suppression by the infection was particularly evident during the initial 24h of the infection, and down modulation of cyclin D3 protein levels were observed at the same time period by immunoblot analysis. The suppression of the Jurkat cell proliferation and the down modulation of cyclin D3 protein level were only induced by viable C. pneumoniae infection, not by exposure to UV-killed or heat-killed C. pneumoniae. Phosphorylations at Thr308 and Ser473 of AKT were induced by C. pneumoniae infection; however, phosphorylation at Thr389 of the downstream kinase, p70S6K was inhibited by unidentified mechanism associated with C. pneumoniae infection. Taking into account that G1 arrest of the C. pneumoniae infected Jurkat cells were not observed and that p70S6K is one of the most important regulators of protein synthesis, it was suggested that the suppression of Jurkat cell proliferation by C. pneumoniae was at least in part mediated by down modulation of protein synthesis through attenuation of Thr389 phosphorylation of p70S6K.

Chlamydia trachomatis induces anti-inflammatory effect in human macrophages by attenuation of immune mediators in Jurkat T-cells

The chronic course of Chlamydia trachomatis infection is subtle with no obvious unusual inflammatory change. The reason for this is not clear. The data reported here explain how macrophage usual inflammatory response switches to anti-inflammatory response during C. trachomatis infection of mixed culture of macrophages and Jurkat T-cells. We assessed the establishment of productive infection in individual or mixed cell culture models, determined the status of C. trachomatis in the cells by monitoring HSP-60:MOMP or the proportions of the estimated IFUs that shed HSP-60 or MOMP. Also, the specific time-course expression of IL-12, IL-10 and IFN-γ or IL-12R, IL-10R, and IFN-γ-R during infection of cell models was assessed. Finally, the early events in cytokine elaboration in circumstances of varying intracellular Ca²⁺ levels were determined. There was evidence of productive infection in all individual and mixed cell culture models. The shedding of HSP-60 was highest in THP-1/Jurkat mixed cell culture model. The proportions of IFU that shed HSP-60 was heightened in infected THP-1/Jurkat mixed culture model, while the proportion of IFU that shed MOMP was higher in infected macrophage/Jurkat mixed culture and infected macrophages only. There was profound early elaboration of IL-10, varying significantly from IL-12 and IFN-γ in all infected individual or mixed cell culture models except in the case of Jurkat; where all cytokine elaboration was downregulated. The receptor to IL-10 was upregulated in infected macrophage/Jurkat cells and THP-1/Jurkat cells compared with other models in which IL-12 and IFN-γ receptors were more expressed. There was no observed significant change in cytokine in any model following the impairment of intracellular Ca²⁺ except in the case of macrophage/Jurkat cell model in which IL-12 and IL-10 were upregulated in 1h or 3 h, respectively. The implication of these findings is that C. trachomatis mediates a switch from inflammatory to anti-inflammatory function in macrophages due to downregulation of the regulatory cytokine, IFN-γ in Jurkat cells, culminating in C. trachomatis chronic course.

Chlamydia pneumoniae inhibits activated human T lymphocyte proliferation by the induction of apoptotic and pyroptotic pathways

Chlamydia pneumoniae is an omnipresent obligate intracellular bacterial pathogen that infects numerous host species. C. pneumoniae infections of humans are a common cause of community acquired pneumonia but have also been linked to chronic diseases such as atherosclerosis, Alzheimer's disease, and asthma. Persistent infection and immune avoidance are believed to play important roles in the pathophysiology of C. pneumoniae disease. We found that C. pneumoniae organisms inhibited activated but not nonactivated human T cell proliferation. Inhibition of proliferation was pathogen specific, heat sensitive, and multiplicity of infection dependent and required chlamydial entry but not de novo protein synthesis. Activated CD4(+) and CD8(+) T cells were equally sensitive to C. pneumoniae antiproliferative effectors. The C. pneumoniae antiproliferative effect was linked to T cell death associated with caspase 1, 8, 9, and IL-1β production, indicating that both apoptotic and pyroptotic cellular death pathways were activated after pathogen-T cell interactions. Collectively, these findings are consistent with the conclusion that C. pneumoniae could induce a local T cell immunosuppression and inflammatory response revealing a possible host-pathogen scenario that would support both persistence and inflammation.

Chlamydophila pneumoniae attachment and infection in low proteoglycan expressing human lymphoid Jurkat cells

This study investigated the proteoglycan (PG)-dependent mechanism of Chlamydophila pneumoniae attachment to lymphocytic cells. Lymphoid Jurkat cells and epithelial HEp-2 cells were statically infected with C. pneumoniae (TW183). Transmission electron microscopy and assessment of inclusion-forming units indicated that the bacteria grew normally in Jurkat cells and were capable of producing secondary infection; however, they grew at a slower rate than in HEp-2 cells. RT-PCR analysis indicated that HEp-2 cells strongly expressed PG-core protein encoding genes, thereby sustaining glycosaminoglycans (GAGs), such as heparin, on the cellular surface. Similar gene expression levels were not observed in Jurkat cells, with the exception of glypican-1. Immunofluorescence analysis also supported strong heparin expression in HEp-2 cells and minimal expression in Jurkat cells, although heparan sulfate pretreatment significantly inhibited bacterial attachment to both cell types. Immunofluorescent co-staining with antibodies against chlamydial LPS and heparin did not identify bacterial and heparin co-localization on Jurkat cells. We also confirmed that when C. pneumoniae was statically infected to human CD4(+) peripheral blood lymphocytes known not expressing detectable level of heparin, the bacteria attached to and formed inclusion bodies in the cells. Thus, the attachment mechanism of C. pneumoniae to Jurkat cells with low PG expression is unique when compared with HEp-2 cells and potentially independent of GAGs such as heparin.