CD200R1 Supports HSV-1 Viral Replication and Licenses Pro-Inflammatory Signaling Functions of TLR2

The CD200R1:CD200 axis is traditionally considered to limit tissue inflammation by down-regulating pro-inflammatory signaling in myeloid cells bearing the receptor. We generated CD200R1−/− mice and employed them to explore both the role of CD200R1 in regulating macrophage signaling via TLR2 as well as the host response to an in vivo, TLR2-dependent model, herpes simplex virus 1 (HSV-1) infection. CD200R1−/− peritoneal macrophages demonstrated a 70–75% decrease in the generation of IL-6 and CCL5 (Rantes) in response to the TLR2 agonist Pam2CSK4 and to HSV-1. CD200R1−/− macrophages could neither up-regulate the expression of TLR2, nor assemble a functional inflammasome in response to HSV-1. CD200R1−/− mice were protected from HSV-1 infection and exhibited dysfunctional TLR2 signaling. Finally, both CD200R1−/− mice and CD200R1−/− fibroblasts and macrophages showed a markedly reduced ability to support HSV-1 replication. In summary, our data demonstrate an unanticipated and novel requirement for CD200R1 in “licensing” pro-inflammatory functions of TLR2 and in limiting viral replication that are supported by ex vivo and in vivo evidence

CD200R1 Supports HSV-1 Viral Replication and Licenses Pro-Inflammatory Signaling Functions of TLR2

The CD200R1:CD200 axis is traditionally considered to limit tissue inflammation by down-regulating pro-inflammatory signaling in myeloid cells bearing the receptor. We generated CD200R1−/− mice and employed them to explore both the role of CD200R1 in regulating macrophage signaling via TLR2 as well as the host response to an in vivo, TLR2-dependent model, herpes simplex virus 1 (HSV-1) infection. CD200R1−/− peritoneal macrophages demonstrated a 70–75% decrease in the generation of IL-6 and CCL5 (Rantes) in response to the TLR2 agonist Pam2CSK4 and to HSV-1. CD200R1−/− macrophages could neither up-regulate the expression of TLR2, nor assemble a functional inflammasome in response to HSV-1. CD200R1−/− mice were protected from HSV-1 infection and exhibited dysfunctional TLR2 signaling. Finally, both CD200R1−/− mice and CD200R1−/− fibroblasts and macrophages showed a markedly reduced ability to support HSV-1 replication. In summary, our data demonstrate an unanticipated and novel requirement for CD200R1 in “licensing” pro-inflammatory functions of TLR2 and in limiting viral replication that are supported by ex vivo and in vivo evidence

T-bet knockout prevents Helicobacter felis-induced gastric cancer

Helicobacter infection is the primary risk factor for gastric cancer, with the cytokine environment within the gastric mucosa the strongest predictor of disease risk. Elevated TNF-alpha, IL-1beta, and low IL-10 are associated with the highest risk. In this study, we used C57BL/6 mice to identify T-bet as a central regulator of the cytokine environment during Helicobacter felis infection. We infected male and female C57BL/6 and C57BL/6-T-bet knockout (KO) litter mates with H. felis and examined the bacterial colonization, immune response, and mucosal damage at varying time points. T-bet KO mice maintained infection for 15 mo at similar levels to wild-type mice. Infection and immune response did not differ between male and female mice. Despite sustained infection, T-bet KO mice respond with a blunted Th1 response associated with preservation of parietal and chief cells and protection from the development of gastric cancer. Unexpectedly, T-bet KO mice develop a gastric environment that would not be expected based on the phenotype of T-bet KO CD4 cells alone. T-bet KO mice respond to H. felis infection with a markedly blunted IL-1beta and TNF-alpha and elevated IL-10 levels. Activity of this one master regulator modulates the expression of the key gastric mucosal cytokines associated with gastric cancer and may be a target for therapy to restore immune balance clinically in patients at risk for gastric cancer

Respiratory syncytial virus activates innate immunity through Toll-like receptor 2

Respiratory syncytial virus (RSV) is a common cause of infection that is associated with a range of respiratory illnesses, from common cold-like symptoms to serious lower respiratory tract illnesses such as pneumonia and bronchiolitis. RSV is the single most important cause of serious lower respiratory tract illness in children (TLRs) activate innate and acquired immunity and are candidates for playing key roles in the host immune response to RSV. Leukocytes express TLRs, including TLR2, TLR6, TLR3, TLR4, and TLR7, that can interact with RSV and promote immune responses following infection. Using knockout mice, we have demonstrated that TLR2 and TLR6 signaling in leukocytes can activate innate immunity against RSV by promoting tumor necrosis factor alpha, interleukin-6, CCL2 (monocyte chemoattractant protein 1), and CCL5 (RANTES). As previously noted, TLR4 also contributes to cytokine activation (L. M. Haynes, D. D. Moore, E. A. Kurt-Jones, R. W. Finberg, L. J. Anderson, and R. A. Tripp, J. Virol. 75:10730-10737, 2001, and E. A. Kurt-Jones, L. Popova, L. Kwinn, L. M. Haynes, L. P. Jones, R. A. Tripp, E. E. Walsh, M. W. Freeman, D. T. Golenbock, L. J. Anderson, and R. W. Finberg, Nat. Immunol. 1:398-401, 2000). Furthermore, we demonstrated that signals generated following TLR2 and TLR6 activation were important for controlling viral replication in vivo. Additionally, TLR2 interactions with RSV promoted neutrophil migration and dendritic cell activation within the lung. Collectively, these studies indicate that TLR2 is involved in RSV recognition and subsequent innate immune activation

The transcriptional repressor BLIMP1 curbs host defenses by suppressing expression of the chemokine CCL8

The transcriptional repressor B lymphocyte-induced maturation protein 1 (BLIMP1) is a master regulator of B and T cell differentiation. To examine the role of BLIMP1 in innate immunity, we used a conditional knockout (CKO) of Blimp1 in myeloid cells and found that Blimp1 CKO mice were protected from lethal infection induced by Listeria monocytogenes. Transcriptome analysis of Blimp1 CKO macrophages identified the murine chemokine (C-C motif) ligand 8, CCL8, as a direct target of Blimp1-mediated transcriptional repression in these cells. BLIMP1-deficient macrophages expressed elevated levels of Ccl8, and consequently Blimp1 CKO mice had higher levels of circulating CCL8, resulting in increased neutrophils in the peripheral blood, promoting a more aggressive antibacterial response. Mice lacking the Ccl8 gene were more susceptible to L. monocytogenes infection than were wild-type mice. Although CCL8 failed to recruit neutrophils directly, it was chemotactic for gamma/delta T cells, and CCL8-responsive gamma/delta T cells were enriched for IL-17F. Finally, CCL8-mediated enhanced clearance of L. monocytogenes was dependent on gamma/delta T cells. Collectively, these data reveal an important role for BLIMP1 in modulating host defenses by suppressing expression of the chemokine CCL8

Trefoil Family Factor 2 Is Expressed in Murine Gastric and Immune Cells and Controls both Gastrointestinal Inflammation and Systemic Immune Responses

Trefoil family factor 2 (TFF2), also known as spasmolytic peptide, is a low-molecular-weight protein that is upregulated in gastric tissues infected with Helicobacter or having other inflammatory conditions, but a precise function is yet to be elucidated. The role of TFF2 in the development of gastritis, colitis, and inflammatory cytokine responses was examined both in vivo and in vitro using wild-type and TFF2 knockout mice. TFF2 knockout and wild-type mice were infected with Helicobacter felis (H. felis) to induce gastritis. Colitis was induced in TFF2 knockout and wild-type mice by administering dextran sodium sulfate (DSS) in drinking water. Histopathology, clinical disease (colitis), and antibody levels (H. felis) were examined. TFF2 expression in tissues was determined by reverse transcriptase PCR, and the inflammatory and proliferative responses of TFF2-expressing macrophages and spleen cells were examined by cytokine enzyme-linked immunosorbent assay, thymidine incorporation, and gene array studies. TFF2 knockout mice have increased susceptibility to H. felis-induced gastritis, with enhanced gastric inflammation. They were also more susceptible to DSS-induced colitis, with prolonged colonic hemorrhage and persistent weight loss. Remarkably, TFF2 expression was not limited to the gastrointestinal tract, as suggested in previous studies, but was also present in macrophages and lymphocytes. The inflammatory and proliferative responses of these immune cell types were dysregulated in TFF2 knockout mice. TFF2(−/−) cells were hyperresponsive to interleukin 1 beta stimulation but showed normal responses to lipopolysaccharide, suggesting a specific role for TFF2 in interleukin 1 receptor but not Toll-like receptor 4 signaling via their Toll-interleukin 1 resistance domains. TFF2(−/−) lymphocytes also produced higher levels of interleukin 2 than wild-type cells. Thus, TFF2 was expressed in the gastrointestinal cells and in immune cells and was a negative regulator of gastrointestinal inflammation and immune cell cytokine responses. Our studies suggest that TFF2 not only controls gastrointestinal repair but also regulates mononuclear cell inflammatory responses