IL-21/IL-21R Signaling Aggravated Respiratory Inflammation Induced by Intracellular Bacteria through Regulation of CD4+ T Cell Subset Responses.

The IL-21/IL-21R interaction plays an important role in a variety of immune diseases; however, the roles and mechanisms in intracellular bacterial infection are not fully understood. In this study, we explored the effect of IL-21/IL-21R on chlamydial respiratory tract infection using a chlamydial respiratory infection model. The results showed that the mRNA expression of IL-21 and IL-21R was increased in Chlamydia muridarum-infected mice, which suggested that IL-21 and IL-21R were involved in host defense against C. muridarum lung infection. IL-21R-/- mice exhibited less body weight loss, a lower bacterial burden, and milder pathological changes in the lungs than wild-type (WT) mice during C. muridarum lung infection. The absolute number and activity of CD4+ T cells and the strength of Th1/Th17 responses in IL-21R-/- mice were significantly higher than those in WT mice after C. muridarum lung infection, but the Th2 response was weaker. Consistently, IL-21R-/- mice showed higher mRNA expression of Th1 transcription factors (T-bet/STAT4), IL-12p40, a Th17 transcription factor (STAT3), and IL-23. The mRNA expression of Th2 transcription factors (GATA3/STAT6), IL-4, IL-10, and TGF-ß in IL-21R-/- mice was significantly lower than that in WT mice. Furthermore, the administration of recombinant mouse IL-21 aggravated chlamydial lung infection in C57BL/6 mice and reduced Th1 and Th17 responses following C. muridarum lung infection. These findings demonstrate that IL-21/IL-21R may aggravate chlamydial lung infection by inhibiting Th1 and Th17 responses.

IL-27/IL-27R Mediates Protective Immunity against Chlamydial Infection by Suppressing Excessive Th17 Responses and Reducing Neutrophil Inflammation.

IL-27, a heterodimeric cytokine of the IL-12 family, has diverse influences on the development of multiple inflammatory diseases. In this study, we identified the protective role of IL-27/IL-27R in host defense against Chlamydia muridarum respiratory infection and further investigated the immunological mechanism. Our results showed that IL-27 was involved in C. muridarum infection and that IL-27R knockout mice (WSX-1-/- mice) suffered more severe disease, with greater body weight loss, higher chlamydial loads, and more severe inflammatory reactions in the lungs than C57BL/6 wild-type mice. There were excessive IL-17-producing CD4+ T cells and many more neutrophils, neutrophil-related proteins, cytokines, and chemokines in the lungs of WSX-1-/- mice than in wild-type mice following C. muridarum infection. In addition, IL-17/IL-17A-blocking Ab treatment improved disease after C. muridarum infection in WSX-1-/- mice. Overall, we conclude that IL-27/IL-27R mediates protective immunity during chlamydial respiratory infection in mice by suppressing excessive Th17 responses and reducing neutrophil inflammation.

IL-21/IL-21R Regulates the Neutrophil-Mediated Pathologic Immune Response during Chlamydial Respiratory Infection.

IL-21/IL-21R was documented to participate in the regulation of multiple infection and inflammation. During Chlamydia muridarum (C. muridarum) respiratory infection, our previous study had revealed that the absence of this signal induced enhanced resistance to infection with higher protective Th1/Th17 immune responses. Here, we use the murine model of C. muridarum respiratory infection and IL-21R deficient mice to further identify a novel role of IL-21/IL-21R in neutrophilic inflammation. Resistant IL-21R-/- mice showed impaired neutrophil recruitment to the site of infection. In the absence of IL-21/IL-21R, pulmonary neutrophils also exhibited reduced activation status, including lower CD64 expression, MPO activity, and neutrophil-produced protein production. These results correlated well with the decrease of neutrophil-related chemokines (KC and MIP-2), inflammatory cytokines (IL-6, IL-1ß, and TNF-α), and TLR/MyD88 pathway mediators (TLR2, TLR4, and MyD88) in infected lungs of IL-21R-/- mice than normal mice. Complementarily, decreased pulmonary neutrophil infiltration, activity, and levels of neutrophilic chemotactic factors and TLR/MyD88 signal in infected lungs can be corrected by rIL-21 administration. These results revealed that IL-21/IL-21R may aggravate the neutrophil inflammation through regulating TLR/MyD88 signal pathway during chlamydial respiratory infection.

Vγ4+ T Cells: A Novel IL-17-Producing γδ T Subsets during the Early Phase of Chlamydial Airway Infection in Mice.

Our previous studies showed that γδ T cells provided immune protection against Chlamydial muridarum (Cm), an obligate intracellular strain of chlamydia trachomatis, lung infection by producing abundant IL-17. In this study, we investigated the proliferation and activation of lung γδ T cell subsets, specifically the IL-17 and IFNγ production by them following Cm lung infection. Our results found that five γδ T cell subsets, Vγ1+ T, Vγ2+ T, Vγ4+ T, Vγ5+ T, and Vγ6+ T, expressed in lungs of naïve mice, while Cm lung infection mainly induced the proliferation and activation of Vγ4+ T cells at day 3 p.i., following Vγ1+ T cells at day 7 p.i. Cytokine detection showed that Cm lung infection induced IFNγ secretion firstly by Vγ4+ T cells at very early stage (day 3) and changed to Vγ1+ T cells at midstage (day 7). Furthermore, Vγ4+ T cell is the main γδ T cell subset that secretes IL-17 at the very early stage of Cm lung infection and Vγ1+ T cell did not secrete IL-17 during the infection. These findings provide in vivo evidence that Vγ4+T cells are the major IL-17 and IFNγ-producing γδ T cell subsets at the early period of Cm lung infection.

Chlamydia muridarum infection induces CD4+ T cells apoptosis via PI3K/AKT signal pathway.

Apoptosis is essential for the homeostatic control of the lymphocytes number during the development of an immune response to an invasive microorganism. CD4+ T cells play a major role in homeostasis of the immune system and are sufficient to confer protection against Chlamydia muridarum (Cm) infection in mice. The present study demonstrated that phosphatidylinositol 3-kinase (PI3K) p110δ mRNA and phosphorylation of protein kinase B (p-AKT) level were significantly increased in lung cells and spleen cells at day 3 and day 7 post-infection, p-AKT level was inhibited when adding PI3K inhibitor LY294002. Moreover, Cm infection induced high levels of IL-2/IL-2Rα in CD4+ T cells, which may relate to PI3K/AKT signal pathway activation. We observed that Cm infection significantly induced apoptosis of CD4+ T cells. The related apoptosis proteins Bcl-2 and Mcl-1 uneven expression levels were induced in CD4+ T cells by Cm infection. These findings provided in vivo and in vitro evidence that Cm infection induces CD4+ T cells apoptosis possibly via PI3K/AKT signal pathway.

The p110δ isoforme of phosphatidylinositol 3-kinase plays an important role in host defense against chlamydial lung infection through influencing CD4+ T-cell function.

PI3Ks display integrant significance in T-cell development and differentiation, which is related to host defense against infections. Here, we investigated the role of p110δ isoform of PI3Ks in host defense against chlamydial lung infection in a mouse model. Our data showed that lung infection with Chlamydia muridarum (Cm) activated PI3K/AKT signaling pathway. Compared to WT mice, p110δD910A mice, mice with an inactivating knockin mutation in the p110δ Isoform of PI3Ks, showed more sever disease phenotype and slower recovery, which was associated with reduced Chlamydia-specific Th1 and Th17 immune responses following infection. Further adoptive transfer experiment showed that mice which received CD4+ T cells from infected p110δD910A mice exhibited greater body weight loss and higher bacterial loads in the lung than those which received CD4+ T cells from WT mice following challenge infection. These results provide in vivo evidence that p110δ isoform of PI3Ks plays an important role in host defense against chlamydial infection by promoting CD4+ T-cell immunity.

Transactivation of proto-oncogene c-Myc by hepatitis B virus transactivator MHBst167.

C-terminally truncated hepatitis B virus (HBV) middle size surface proteins (MHBst) has been shown to be a transcriptional activator and may be relevant to hepatocarcinogenesis by transactivating gene expression. In the present study, a pcDNA3.1(-)-MHBst167 vector coding for MHBst truncated at amino acid 167 (MHBst167) was constructed and transfected into the HepG2 hepatoma cell line. mRNA and protein expression of MHBst167 in the cells was detected by reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis. A cDNA library of genes transactivated by the truncated protein in HepG2 cells was made in pGEM-T Easy using suppression subtractive hybridization. The cDNAs were sequenced and analyzed with BLAST searching against the sequences in GenBank. The results showed that certain sequences, such as that of human proto-oncogene c-Myc, may be involved in tumor development. An expression vector pCAT3/c-Myc containing the chloramphenicol acetyltransferase (CAT) gene under the control of a c-Myc promoter was generated, and the transcriptional transactivating effect of MHBst167 on the c-Myc promoter was investigated by RT-PCR and western blotting. MHBst167 was found to upregulate the transcriptional activity of the promoter, as well as transcription and translation of c-Myc. MHBst167 was also shown to transactivate SV40 immediate early promoter, and transcriptionally transactivate the expression of human c-Myc. These findings provide new directions for studying the biological functions of MHBst167, and for a better understanding of the tumor development mechanisms of HBV infection.