Reversion of the antichlamydial effect of tumor necrosis factor by tryptophan and antibodies to beta interferon.

Human recombinant tumor necrosis factor-alpha (TNF-alpha) inhibited the growth of Chlamydia trachomatis (L2/434/Bu) in HEp-2 cells. The effect was synergistic with that of gamma interferon (IFN-gamma). TNF-induced resistance to chlamydiae could be blocked with cycloheximide, suggesting that it involves the function of some induced proteins. Tryptophan degradation was enhanced in the TNF-treated cells and was much further increased when the cells were treated with both TNF and IFN-gamma at concentrations at which IFN-gamma by itself had very little effect. Antibodies to IFN-beta blocked the augmentation of tryptophan degradation by TNF and decreased but did not fully eliminate the antichlamydial effect of TNF. Increased concentration of tryptophan in the growth medium (greater than 100 micrograms/ml) resulted in reversion of the antichlamydial effect of TNF. This study suggests that the inhibition of chlamydial growth by TNF is mediated partly through an autocrine function of IFN-beta which, in synergism with TNF, enhances the activity of a tryptophan-degrading enzyme(s) and partly by some other activities of TNF which can be blocked by tryptophan.     

Failure to detect cell-mediated cytotoxicity against Chlamydia trachomatis-infected cells.

Mice were infected with Chlamydia trachomatis (L2/434) and at various intervals after infection their lymphoid cells were tested directly for cytotoxic activity against Chlamydia-infected L929 cells. In a modified cell-mediated lympholysis assay, splenic, lymph node, and peritoneal exudate cells did not significantly cause the destruction of the infected targets, although infection did result in the formation of antichlamydial antibodies. Whereas chlamydial antigens are capable of activating cell-mediated immunity in other experimental models, our results show that either this chlamydial infection does not induce the generation of cytotoxic effector cells or chlamydial antigens are absent from the surface of infected cells.     

Effect of interferon on the growth of Chlamydia trachomatis in mouse fibroblasts (L cells).

The effect of murine interferon on the growth of the lymphogranuloma venereum biotype of Chlamydia trachomatis (strain 440L) in murine fibroblasts (L cells) was examined. Treatment of infected cell cultures with interferon caused a reduction in the number of inclusion-bearing cells as seen by light and electron microscopy and a decrease in yields of chlamydiae as determined by infectivity assays. Interferon also inhibited cycloheximide-resistant (chlamydia-specific) protein synthesis in infected cells. The interferon effect was dose dependent, with 80 to 90% inhibition occurring at concentrations of greater than 200 IU/ml. The inhibitory effect was neutralized by anti-murine interferon globulin. Interferon did not inactivate extracellular chlamydiae, and both host cell RNA and protein synthesis were required for the development of the interferon-induced antichlamydial state. Inhibition of chlamydial growth by interferon was demonstrable in cells treated 18 h before infection or up to 4 h after infection. Cells infected after interferon was removed exhibited an antichlamydial activity decline which was complete by 30 h after interferon removal. We show that interferon treatment did not affect either entry of chlamydiae into host cells or chlamydial conversion to reticulate bodies but rather caused a reduction in the rate of reticulate body replication.     

Production of prostaglandin E2 in monocytes stimulated in vitro by Chlamydia trachomatis, Chlamydophila pneumoniae, and Mycoplasma fermentans

Chlamydia trachomatis (CT) as well as Chlamydophila pneumoniae (CP) cause chronic inflammatory diseases in humans. Persistently infected monocytes are involved in the pathogenesis by inducing mediators of inflammation. An in vitro system of chlamydial persistence in human peripheral blood monocytes (HPBM) was used to investigate prostaglandin E(2) (PGE(2)) production and the expression of the key enzyme for prostaglandin production, cyclooxygenase-2 (COX-2). PGE(2) production was determined by PGE(2)-ELISA of HPBM-culture supernatants. Cox-2 mRNA expression was measured by real-time RT-PCR of total RNA isolated from HPBM. Both, CT and CP, stimulated PGE(2) production of HPBM in vitro. Equivalent numbers of CT per host cell induced a higher PGE(2)-response compared to CP. The amount of synthesized PGE(2) depended on the chlamydial multiplicity of infection (MOI). Even at an MOI of 10 the amount of CT- and CP-induced prostaglandin, respectively, was lower than the amount of prostaglandin induced by E. coli lipopolysaccharide (LPS) at a concentration of 10microg/ml. In contrast to stimulation with LPS, Chlamydia-induced PGE(2) production as well as cox-2 mRNA decreased after day 1 post infection (p.i.). These data indicate that Chlamydia stimulate PGE(2) production in human monocytes. Since Chlamydia are often contaminated by mycoplasma, the influence of mycoplasma on the prostaglandin production was investigated additionally. Mycoplasma fermentans (MF) also stimulated PGE(2) production. The co-infection of mycoplasma and Chlamydia resulted in an additive effect in the production of PGE(2). Thus it is important to use host cells and Chlamydia free of mycoplasma contamination for the analysis of Chlamydia-induced prostaglandin production.     

Role of chlamydial heat shock protein 60 in the stimulation of innate immune cells by Chlamydia pneumoniae

Chlamydia pneumoniae stimulates potently maturation of and cytokine secretion by bone marrow-derived dendritic cells (BMDDC). BMDDC responses depend mainly on Toll-like receptor (TLR)2 and to a minor extent on TLR4. We demonstrate here using C. pneumoniae in an infectious model with the replication-permissive epithelial cell line HEp2 that HSP60 is produced in substantial amounts in chlamydial inclusions during infection. Electron microscopy of chlamydial inclusions revealed that HSP60 was mainly associated with reticulate bodies, but was also located in between the different chlamydial developmental forms. Supernatants of permissive HEp2 cells infected with C. pneumoniae contained soluble chlamydial HSP60 as demonstrated by Western blotting and were able to stimulate BMDDC of wild-type mice. The stimulatory capacity of culture supernatants correlated with the presence of chlamydial HSP60. In contrast, BMDDC from TLR4-mutant mice crossed to TLR2-deficient mice were not stimulated by the culture supernatant, indicating that chlamydial HSP60 but not cytokines, possibly secreted by infected HEp2 cells, are responsible for the observed stimulation of BMDDC. Purified recombinant HSP60 from C. pneumoniae stimulated BMDDC in a TLR2- and TLR4-dependent fashion similar to the whole microorganism. In summary, these data suggest chlamydial HSP60 as an important mediator of inflammatory responses during infection with C. pneumoniae.     

Prostaglandin E2 modulates dendritic cell function during chlamydial genital infection

Inflammatory responses mediated by antigen-presenting dendritic cells (DCs), can be modulated by the presence of prostaglandins (PG), including prostaglandin E2 (PGE2). PGE2 modifies the production of an immune response by altering DC function through PGE2 receptors. PGE2 is produced by epithelial cells lining the murine female reproductive tract during Chlamydia muridarum infection and likely manipulates the antichlamydial immune response during antigen uptake in the genital mucosa. Our data demonstrate that the PGE2 present locally in the genital tract upon chlamydial genital infection enhanced the recruitment of CD11b+ conventional DCs, but not CD45R+ plasmacytoid DCs, to infected genital tract tissue and draining lymph nodes in vivo. Furthermore, exposure to PGE2 in vitro during infection of murine bone-marrow-derived conventional DCs (cDCs) boosted interleukin-10 mRNA and protein while not influencing interleukin-12p40 production. Infection of cDCs markedly increased mRNA production of the costimulatory molecules CD86, CD40 and a member of the C-type lectin family, DEC-205, but addition of PGE2 increased other costimulatory molecules and C-type lectins. Also, exposure of PGE2 to infected cDCs increased FcgammaRIII and FcgammaRIIb, suggesting that PGE2 enhances the uptake and presentation of C. muridarum and augments production of the antichlamydial adaptive immune response. Taken together, the data suggest that exposure of infected cDCs to PGE2 drives production of a diverse adaptive immune response with implications for regulating tissue inflammation.     

Unraveling the lethal synergism between Trypanosoma cruzi infection and LPS: a role for increased macrophage reactivity

Various infections sensitize to lethal shock by promoting hyperactivation of macrophages to LPS stimulation. Although macrophages are thought to be deactivated upon contact with apoptotic cells during Trypanosoma cruzi infection, T. cruzi infection also sensitizes mice to endotoxemia. Herein, we studied the mechanisms of sensitization to endotoxemia in T. cruzi-infected mice in order to solve the paradox. Live (but not fixed) trypomastigotes from various stocks sensitized mice to endotoxemia. Mice deficient in glycolipid recognition (TLR2(-/-) and CD1d(-/-)) were sensitized by infection to challenge with LPS. Infected mice hyperproduced TNF and IL-10 upon LPS challenge. Infected TNF-R1(-/-), macrophage migration inhibitory factor (MIF)(-/-) and IFN-gamma(-/-) mice were lethally sensitized, but infected TNF-R1(-/-) mice administered anti-MIF survived shock with LPS. Macrophages from infected mice hyperproduced TNF in response to LPS stimulation and displayed increased expression of TLR4 compared to non-infected controls. Treatment with the PGE(2) synthesis inhibitor acetylsalicylic acid (AAS) in vivo reduced parasitemia and enhanced LPS-stimulated production of TNF by macrophages, but the effect was less in infected mice than in normal mice. Nevertheless, AAS treatment did not increase the susceptibility of infected mice to sublethal shock with LPS. Our results point to independent MIF and TNF/TNF-R1 lethal pathways and suggest a role for hyperactivated macrophages in T. cruzi-sensitized LPS-induced shock.     

Activation of lipid metabolism contributes to interleukin-8 production during Chlamydia trachomatis infection of cervical epithelial cells

Chlamydia trachomatis infection is the most common cause of bacterial sexually transmitted diseases. Infection of the urogenital tract by C. trachomatis causes chronic inflammation and related clinical complications. Unlike other invasive bacteria that induce a rapid cytokine/chemokine production, chlamydial infection induces delayed inflammatory response and proinflammatory chemokine production that is dependent on bacterial growth. We present data here to show that the lipid metabolism required for chlamydial growth contributes to Chlamydia-induced proinflammatory chemokine production. By gene microarray profiling, validated with biochemical studies, we found that C. trachomatis LGV2 selectively upregulated PTGS2 (COX2) and PTGER4 (EP4) in cervical epithelial HeLa 229 cells. COX2 is an enzyme that catalyzes the rate-limiting step of arachidonic acid conversion to prostaglandins, including prostaglandin E2 (PGE2) and other eicosanoids, whereas EP4 is a subtype of cell surface receptors for PGE2. We show that Chlamydia infection induced COX2 protein expression in both epithelial cells and peripheral blood mononuclear cells and promoted PGE2 release. Exogenous PGE2 was able to induce interleukin-8 release in HeLa 229 epithelial cells. Finally, we demonstrated that interleukin-8 induction by Chlamydia infection or PGE2 treatment was dependent on extracellular signal-regulated kinase/mitogen-activated protein activity. Together, these data demonstrate that the host lipid remodeling process required for chlamydial growth contributes to proinflammatory chemokine production. This study also highlights the importance of maintaining a balanced habitat for parasitic pathogens as obligate intracellular organisms.     

Stimulation of Macrophages by Endotoxin Results in the Reactivation of a Persistent Herpes Simplex Virus Infection

Previous work has shown that splenic macrophages derived from herpes simplex virus (HSV)-resistant C57BL/6 mice undergo a persistent HSV infection which is characterized by the continuous release of infectious virus particles from a small subpopulation of infected cells. Treatment of persistently infected macrophages for 2 weeks with lipopolysaccharide (LPS) resulted in an increase of HSV yield and in virus-induced cytopathic effects. HSV was also reactivated by treatment of macrophage cultures with lipid A or tumour necrosis factor (TNF). Like macrophages of C57BL/6 origin, cells from LPS-hyporesponsive C3H/HeJ mice could be persistently infected with HSV. These cells were resistant to LPS-induced virus reactivation. The results show that macrophages derived from C57BL/6 mice are rendered susceptible to lytic HSV infection by treatment with LPS or TNF. Thus, these substances may interfere with persistent HSV infection which can be established due to genetically controlled properties of the host.     

Potentiation of interferon-mediated inhibition of Chlamydia infection by interleukin-1 in human macrophage cultures.

One mechanism by which interferons (IFNs) can inhibit chlamydial infection is by the induction of the enzyme indoleamine 2,3-dioxygenase (IDO), which restricts the availability of tryptophan, which is required for chlamydial growth. Other immunomodulating agents, including interleukin-1 (IL-1), can interact synergistically with IFNs, resulting in increased IDO activity in macrophages. The objectives of this study were to establish that IL-1 can enhance IFN-mediated inhibition of chlamydial growth by increasing the amount of IDO activity induced by IFNs and to identify immunomodulatory agents in culture supernatants from chlamydia-infected macrophages that interact synergistically with IFNs in restricting chlamydial growth. Monocyte-derived macrophages were treated with IL-1 combined with gamma IFN (IFN-gamma) or IFN-beta. The ability of treated cells to support the growth of Chlamydia psittaci was directly related to the amount of IDO activity induced; as IDO activity increased, so did inhibition of chlamydial growth. Furthermore, concentrations of IFNs were identified at which little IDO activity was induced and chlamydial growth was permitted yet which in the presence of IL-1 resulted in increased IDO activity and restriction of chlamydial growth. The addition of exogenous tryptophan reversed the effect of combined IFN and IL-1 treatment, indicating that IDO activity induced by combined cytokine treatment was responsible for chlamydial inhibition. Supernatants from chlamydia-infected macrophages were capable of potentiating IDO induction by IFN-gamma and of restricting the growth of C. psittaci. Antibody to IL-1 beta neutralized the potentiating effects of supernatants from chlamydia-infected cells on both IDO induction and chlamydial inhibition. Thus, IL-1 produced in response to chlamydial infection may contribute to the elimination of the infection.     

Modulation of tumor necrosis factor and gamma interferon production by cocaine and morphine in aging mice infected with LP-BM5, a murine retrovirus.

The actions of retroviral infections, aging, and cocaine and morphine injection on cytokine production were investigated in C57BL/6 female mice. Retroviral infection with LP-BM5 murine leukemia virus was further developed as a model of murine acquired immunodeficiency syndrome (AIDS). The effects of cocaine and morphine on gamma-interferon (IFN) and tumor necrosis factor (TNF) production in vivo and with isolated spleen cells were measured by a sandwich enzyme-linked immunosorbent assay (ELISA) method. Serum IFN was generally not detected in any group except mice injected with saline and young mice infected with LP-BM5 virus. Splenocytes from mice with murine AIDS produced less IFN when stimulated in vitro by ConA. In aged mice, IFN production by spleen cells was severely suppressed by retroviral infection. Cocaine had a tendency to suppress IFN production by stimulated cells in vitro. Morphine tended to reduce IFN production by spleen cells from retrovirally infected animals. The serum TNF level in mice with murine AIDS was elevated creating higher levels in morphine and morphine plus cocaine treated uninfected mice while cocaine injection eliminated serum TNF. When stimulated in vitro by lipopolysaccharides (LPS), splenocytes from mice with murine AIDS also produced more TNF than uninfected controls. TNF production in vitro and in vivo was significantly increased by retroviral infection. Therefore, results indicate that cocaine and retroviral infection modulate TNF and IFN production.     

The Endogenous Balance of Soluble Tumor Necrosis Factor Receptors and Tumor Necrosis Factor Modulates Cachexia and Mortality in Mice Acutely Infected with Trypanosoma cruzi

To better understand the role of tumor necrosis factor (TNF) during Trypanosoma cruzi infection in BALB/c mice, we have investigated the kinetics of circulating tumor necrosis factor (TNF), soluble TNF receptor 1 (sTNR1), and sTNFR2 levels, as well as the interactions between such factors, in relation to parasitemia, cachexia, and mortality of acutely infected animals. Our data show that the parasitemic phase of T. cruzi infection in mice is associated with high levels of circulating TNF and sTNFR2, resulting in the formation of cytokine-receptor complexes and some degree of neutralization of TNF bioactivity. Although sTNR2 levels always exceeded TNF levels, low sTNFR/TNF circulating ratios were associated with cachexia in all infected mice, whereas the lowest ratios were observed in dying animals harboring the highest parasitemia. We also studied the modulation of sTNFR/TNF ratios induced by anti-TNF antibodies administered to infected animals and their consequences on the outcome of the infection. The injection of anti-TNF monoclonal antibody (MAb) TN3 into infected mice resulted in a paradoxical overproduction of TNF (associated with a higher parasitemia), lowered the sTNFR/TNF circulating ratios, and considerably worsened cachexia and mortality of animals. Another anti-TNF MAb (1F3F3) decreased the in vivo availability of TNF as well as parasite levels and reduced cachexia. Altogether, such results highlight that, besides playing a beneficial role early in infection, TNF also triggers harmful effects in the parasitemic phase, which are limited by the in vivo simultaneous endogenous production of soluble receptors.     

Inhibition of CMV replication in human fibroblasts by human monocyte-derived macrophages: implication for CMV persistent infection

The effect of monocytes (M) and monocyte-derived macrophages (MdM) on cytomegalovirus (CMV) replication in human fibroblasts (HF) was studied by one step growth experiments, plaque formation and dot hybridization with a labeled CMV DNA probe. HF were infected with CMV at multiplicities of infection (mol) of 0.001 to 1. After virus adsorption, M or MdM were added at an effector target ratio of 2:1. MdM reduced both infectious viral yield and the quantity of viral DNA and inhibited viral plaque formation. M, however, affected these parameters to a lesser extent. Electron microscopic studies showed that MdM treated CMF-infected HF, 4 days pi, contained only a few capsids in their nuclei and many vacuoles in their cytoplasm as compared to CMV infected HF (control). A reduction of CMV DNA inhibition was observed upon incubation of the infected HF cells with MdM separated from the infected cells by a membrane. Addition of tumor necrosis factor (TNF) antibody to CMV-infected HF incubated with MdM either in direct contact or separated by a membrane from the infected cells reduced the inhibition of CMV-DNA production. The results of this study suggest that MdM may modulate CMV replication in vivo and may also have a role in CMV persistence or chronic infection.     

Effect of prostaglandin E2 on plasma lactic dehydrogenase activity in (NZB x NZW)F1 mice with a chronic infection of lactic dehydrogenase virus.

The effect of prostaglandin E2(PGE2) on blood LDH values was investigated in (NZB x NZW)F1 mice with or without an established infection with lactic dehydrogenase virus (LDV). Plasma LDH decreased in infected mice treated with PGE2, but increased in infected mice treated with indomethacin, an inhibitor of PGE2. However no significant effect on LDH occurred in uninfected mice treated with PGE2 or indomethacin. To investigate the mechanisms of decreased LDH activities resulting from treatment with PGE2, clearance tests were performed. Clearance of LDH-5, but not LDH-1, was faster in PGE2-treated mice than in non-treated mice, whether or not they were infected with LDV. The results suggest that enhanced clearance of LDH-5 in mice treated with PGE2 may account for the fall in plasma LDH in LDV-infected mice.     

Chlamydia pneumoniae inhibits apoptosis in human epithelial and monocyte cell lines

Chlamydia pneumoniae is an obligate intracellular pathogen with a tendency to cause persistent infections that has been associated with many chronic conditions such as asthma and coronary artery disease. However, its immunopathogenic mechanisms are poorly understood. When aiming to study the impact of C. pneumoniae infection on host cell apoptosis, we found that epithelial infected (HL) cells and macrophages (U937-line) were resistant to staurosporine and tumour necrosis factor (TNF)-alpha-induced physiological apoptosis 48, 72 or 120 h post-infection, as determined by flow cytometry, DNA fragmentation assay and fluorescence microscopy. The antiapoptotic influence was observed even at a late stage of the chlamydial life cycle and was dependent on the chlamydial protein synthesis. The mechanisms involved blockage of mitochondrial cytochrome c release and caspase 3 activation. We also found that during a persistent C. pneumoniae infection induced in vitro by penicillin treatment of cell cultures, the inhibition of apoptosis was extended for up to 120 h of follow-up post-infection and was restricted to the cells carrying chlamydial inclusions. Our findings suggest that inhibition of apoptosis may be one of the pathogenetic mechanisms by which C. pneumoniae infection can mediate the development of chronic diseases.     

Tobacco smoke induces a persistent, but recoverable state in Chlamydia pneumoniae infection of human endothelial cells

We investigated the extent to which tobacco smoke could induce persistence of Chlamydia pneumoniae in human endothelial cells. Aortic and coronary artery endothelia were infected in the absence or presence of non-cytotoxic concentrations of tobacco smoke medium. Following exposure to smoke medium, chlamydial inclusions were smaller and demonstrated fewer genome copies as determined by real-time PCR. Enumeration of inclusion-forming units (IFU) established a significant smoke-mediated, dose-dependent inhibition of elementary bodies (EB). Host cell apoptosis did not contribute to the observed restriction of productive infection. Ultrastructure analysis demonstrated an arrest in chlamydial development following smoke-exposure, with a predominance of reticulate bodies (RB) observed inside inclusions. Recovery of viable IFU was achieved with removal of smoke-medium and addition of L-tryptophan. In the presence of smoke, C. pneumoniae infection demonstrated all the characteristics of persistence in human endothelia cells. This is the first time that primary human arterial endothelial cells have been shown to support chlamydial persistence. Tobacco smoke is a well-characterized risk factor for progression of atherosclerosis, but a novel means of inducing chlamydial persistence in vascular cells. Thus, smoking may additionally contribute to atherosclerotic disease by inducing a persistent chlamydial infection in arterial endothelium.     

Characterization of gamma interferon-mediated cytotoxicity to chlamydia-infected fibroblasts.

Addition of murine recombinant gamma interferon (IFN-gamma) to mouse fibroblast cultures infected with Chlamydia psittaci was found to induce a cytotoxic response that was dependent on the concentration of IFN-gamma added and the multiplicity of infection given. No cytotoxicity was observed for uninfected cells treated with IFN-gamma, nor did infection alone elicit cytotoxicity. Cytotoxicity was detected only if IFN-gamma was present for at least the first 18 h of a 30-h incubation period. Cytotoxic activity was not observed when infected cells were treated with 50 micrograms of chloramphenicol per ml, a drug which inhibits differentiation of infectious elementary bodies to noninfectious reticulate bodies. Cytotoxic activity was restored if addition of chloramphenicol was delayed until 18 h postinfection. Addition of 100 U of penicillin per ml to infected host cells reduced but did not abolish cytotoxic activity. Treatment of host cells with as little as 0.2 microgram of cycloheximide per ml inhibited cytotoxicity without interfering with chlamydial growth. When addition of cycloheximide was delayed until 12 h after infection and IFN-gamma treatment, cytotoxicity was restored. These data indicate that IFN-gamma functions as a cytotoxic cytokine against chlamydia-infected fibroblasts. Cytotoxicity was found to be dependent on chlamydial multiplicity of infection, differentiation of chlamydiae to the metabolically active form, and host cell protein synthesis.     

Regulation of chlamydial infection by host autophagy and vacuolar ATPase-bearing organelles

As arguably the most successful parasite, Chlamydia is an obligate intracellular bacterium replicating inside a vacuole of eukaryotic host cells. The chlamydial vacuole does not fuse with the defense cell organelle lysosome. We previously showed that chlamydial infection increases markers of autophagy, an innate antimicrobial activity requiring lysosomal function. However, the work presented here demonstrates that p62, an autophagy protein that is degraded in lysosomes, either remained unchanged or increased in chlamydia-infected human epithelial, mouse fibroblast, and mouse macrophage cell lines. In addition, the activities of three lysosomal enzymes analyzed were diminished in chlamydia-infected macrophages. Bafilomycin A1 (BafA), a specific inhibitor of vacuolar ATPase (vATPase) required for lysosomal function, increased the growth of the human pathogen Chlamydia trachomatis (L2) in wild-type murine fibroblasts and macrophages but inhibited growth in the autophagy-deficient ATG5(-/-) fibroblasts. BafA exhibited only slight inhibition or no effect on L2 growth in multiple human genital epithelial cell lines. In contrast to L2, the mouse pathogen Chlamydia muridarum (MoPn) was consistently inhibited by BafA in all cell lines examined, regardless of species origin and autophagy status. Finally, L2 but not MoPn grew more efficiently in the ATG5(-/-) cells than in wild-type cells. These results suggest that there are two types of vATPase-bearing organelles that regulate chlamydial infection: one supports chlamydial infection, while the other plays a defensive role through autophagy when cells are artificially infected with certain chlamydiae that have not been adapted to the host species.     

Inhibition of lymphocyte CD3 expression by Chlamydophila pneumoniae infection

Since lymphocytes are a major immune cell besides macrophages in the development of atherosclerosis, interaction between lymphocytes and Chlamydophila pneumoniae may contribute to the pathogenesis of chronic inflammatory diseases associated with C. pneumoniae. In this regard, we examined a possible alteration of CD3 expression of human lymphocyte Molt-4 cells by C. pneumoniae infection. The expression levels of CD3 molecules of lymphocyte Molt-4 cells were significantly decreased by C. pneumoniae infection. In contrast, heat-killed C. pneumoniae as well as mock (cell lysates) did not cause any alteration of CD3 expression of the cells. Treatment of the infected cells with NS-398 (cyclo-oxyganase-2 inhibitor) or AH-23848 (EP(4) prostanoid receptor antagonist) abolished the inhibition of CD3 expression. The enhanced prostaglandin E(2) (PGE(2)) productions in the culture supernatants of infected cells were confirmed by competitive enzyme-immunosorbent assay (ELISA). C. pneumoniae infection of enriched lymphocytes from human peripheral blood mononuclear cells also induced a decrease of CD3 expression. Thus, C. pneumoniae infection of lymphocytes induces a decrease of CD3 expression mediated by possibly PGE(2) production.