Effector CD4+ T cell subsets, whose differentiation is facilitated by distinct cytokine cues, amplify the corresponding type of inflammatory response. Regulatory T (Treg) cells integrate environmental cues to suppress particular types of inflammation. In this regard, STAT3, a transcription factor essential for T helper 17 (Th17) cell differentiation, is necessary for Treg cell-mediated control of Th17 cell responses. Here, we showed that anti-inflammatory interleukin-10 (IL-10), and not pro-inflammatory IL-6 and IL-23 cytokine signaling, endowed Treg cells with the ability to suppress pathogenic Th17 cell responses. Ablation of the IL-10 receptor in Treg cells resulted in selective dysregulation of Th17 cell responses and colitis similar to that observed in mice harboring STAT3-deficient Treg cells. Thus, Treg cells limit Th17 cell inflammation by serving as principal amplifiers of negative regulatory circuits operating in immune effector cells.

The expression of the chemokine receptor XCR1 and the function of its ligand XCL1 (otherwise referred to as ATAC, lymphotactin, or SCM-1) remained elusive to date. In the present report we demonstrated that XCR1 is exclusively expressed on murine CD8(+) dendritic cells (DCs) and showed that XCL1 is a potent and highly specific chemoattractant for this DC subset. CD8(+) T cells abundantly secreted XCL1 8-36 hr after antigen recognition on CD8(+) DCs in vivo, in a period in which stable T cell-DC interactions are known to occur. Functionally, XCL1 increased the pool of antigen-specific CD8(+) T cells and their capacity to secrete IFN-gamma. Absence of XCL1 impaired the development of cytotoxicity to antigens cross-presented by CD8(+) DCs. The XCL1-XCR1 axis thus emerges as an integral component in the development of efficient cytotoxic immunity in vivo.

An invading pathogen must be held in check by the innate immune system until a specific immune response can be mounted. In the case of Gram-negative bacteria, the principal stimulator of the innate immune system is lipopolysaccharide (LPS), a component of the bacterial outer membrane. In vitro, LPS is bound by lipopolysaccharide-binding protein (LBP) and transferred to CD14--the LPS receptor on the macrophage surface--or to high-density lipoprotein (HDL) particles. Transfer to CD14 triggers an inflammatory response which is crucial for keeping an infection under control. Here we investigate how LBP functions in vivo by using LBP-deficient mice. Surprisingly, we find that LBP is not required in vivo for the clearance of LPS from the circulation, but is essential for the rapid induction of an inflammatory response by small amounts of LPS or Gram-negative bacteria and for survival of an intraperitoneal Salmonella infection.

Background and Purpose-Recent studies have attributed the increased infection vulnerability of patients with stroke to stroke-induced immunosuppression. We have therefore explored the immunological changes in patients with ischemic stroke. Methods-Blood from 46 patients with stroke was analyzed by fluorescent-activated cell sorter to determine leukocyte subsets. To identify changes that represent clinically relevant immunosuppression, we compared patients who developed infection within 14 days after stroke with those who did not. Results-Stroke induced a dramatic and immediate loss of T-lymphocytes, most pronounced within 12 hours after stroke onset. Only patients with subsequent infection exhibited a delay in the recovery of CD4ϩ T-lymphocyte counts. Conclusions-Our data suggest that a loss of CD4ϩ T cell function contributes to the stroke-induced immunosuppression.The CD4ϩ T cell count on the day after stroke may emerge as a predictive marker for poststroke infection allowing, early identification of patients at risk. (Stroke. 2008;39:237-241.)

Strain C57BL/6 mice produce a highly restricted primary response to the (4-hydroxy-3-nitrophenyl)acetyl (NP) group. This response is composed of molecules having mu or gamma1 heavy chains and light chains of the lambda type. A guinea pig anti-idiotype was raised to the purified C57BL/6 primary anti-NP immunoglobulin. After suitable absorption, this anti-idiotype was shown to detect markers present on the primary anti-NP immunoglobulin only of those strains which express the Ig-1b allotype. Breeding experiments demonstrated that the marker segregated with the heavy chain linkage group.

IL-10 is a potent regulator of the innate and adaptive immune responses. Several cell types produce IL-10 and its receptor chains and these may regulate different immune responses. Here we report that inactivation of the IL-10 receptor (IL-10R1) gene in mice leads to an increased susceptibility to chemically induced colitis as in the classical IL-10-deficient mutant. To identify the cells regulated by IL-10 in immune responses, we generated several cell type specific IL-10R1-deficient mutants. We show that, in an IL-10-dependent LPS model of endotoxemia, dampening of the immune response requires expression of IL-10R1 in monocytes/macrophages and/or neutrophils but not in T cells nor B cells. As the macrophage and/or neutrophil-specific IL-10-deficient mutants also display the same phenotype, our results suggest that an autocrine loop in monocytes/macrophages is the most probable mechanism for the regulation of an LPS-induced septic shock. In contrast, in an IL-10-regulated T-cell response to Trichuris muris infection, IL-10 acting on T cells or monocytes/macrophages/neutrophils is not critical for the control of the infection.

Respiratory syncytial virus (RSV) infection is the leading viral cause of severe lower respiratory tract illness in young infants. Clinical studies have documented that certain polymorphisms in the gene encoding the regulatory cytokine IL-10 are associated with the development of severe bronchiolitis in RSV infected infants. Here, we examined the role of IL-10 in a murine model of primary RSV infection and found that high levels of IL-10 are produced in the respiratory tract by anti-viral effector T cells at the onset of the adaptive immune response. We demonstrated that the function of the effector T cell -derived IL-10 in vivo is to limit the excess pulmonary inflammation and thereby to maintain critical lung function. We further identify a novel mechanism by which effector T cell-derived IL-10 controls excess inflammation by feedback inhibition through engagement of the IL-10 receptor on the antiviral effector T cells. Our findings suggest a potentially critical role of effector T cell-derived IL-10 in controlling disease severity in clinical RSV infection.

As a key receptor for lipopolysaccharide (LPS) on the surface of monocytes and macrophages, the CD14 molecule is primarily involved in non-specific host defense mechanisms against gram-negative bacteria. To delineate the structural basis of LPS binding, 23 mutants in the N-terminal 252 amino acids of human CD14 were generated and stably transfected into CHO cells. In each mutant, a block of five amino acids was substituted by alanine. Reactivity of the mutants with anti-CD14 mAbs, and their ability to interact with LPS and Escherichia coli were tested. serum, which is directly secreted or derived from protease-dependent shedding of the membrane-bound molecule [l 1 -141. As a soluble LPS-receptor, sCD14 competes with mCDt4 for LPS binding and is able to neutralize LPS-induced responses in vitro and in vivo [7,[15][16][17]. In addition to this, however, sCD14 mediates the LPS-induced activation of non-CD14-expressing endothelial, epithelial and smooth-muscle cells 118-221.Because the LPS molecule and its receptor and carrier proteins are primary targets for therapeutic-intervention strategies, the knowledge of ligand-receptor interactions on a molecular level may provide a rationale for the development of specific drugs that interfere with LPS binding or with LPS signaling. Therefore, different approaches have been used to identify the LPS-binding domain of human CDI 4. Viriyakosol and Kirkland 1231 constructed a series of small deletion mutants of the hydrophilic regions within the first 65 residues of the mature protein. They could not demonstrate serum-dependent binding of 'H-labeled LPS to any of their mutant proteins, though only CHO cells transfected with a deletion mutant spanning amino acids 35-39 failed to respond to LPS by translocation of NFKB. By sequential deletion of the C-terminal part of the molecule, Juan et al. [24] showed that CD14-(1-152)-peptide is able to recognize LPS and to mediate cellular responses induced by LPS. In a further study from the same group, an epitope of CD14 was defined, which is protected by LPS from cleavage by endoproteinase Asp-N 1251. They showed that a deletion mutant covering amino acids 57-64 does not interact with LPS In this study we have performed an alanine scan of amino acids 1 to 152 of human CD14. 23 alanine-substitution mutants have been constructed and stably expressed in CHO cells. We analyzed whether mutant proteins expressed on the surface of 1261.