▪ Abstract The innate immune system is a universal and ancient form of host defense against infection. Innate immune recognition relies on a limited number of germline-encoded receptors. These receptors evolved to recognize conserved products of microbial metabolism produced by microbial pathogens, but not by the host. Recognition of these molecular structures allows the immune system to distinguish infectious nonself from noninfectious self. Toll-like receptors play a major role in pathogen recognition and initiation of inflammatory and immune responses. Stimulation of Toll-like receptors by microbial products leads to the activation of signaling pathways that result in the induction of antimicrobial genes and inflammatory cytokines. In addition, stimulation of Toll-like receptors triggers dendritic cell maturation and results in the induction of costimulatory molecules and increased antigen-presenting capacity. Thus, microbial recognition by Toll-like receptors helps to direct adaptive immune responses ...

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Innate Immune Recognition

Mutations of the gene Lps selectively impede lipopolysaccharide (LPS) signal transduction in C3H/HeJ and C57BL/10ScCr mice, rendering them resistant to endotoxin yet highly susceptible to Gram-negative infection. The codominant Lpsd allele of C3H/HeJ mice was shown to correspond to a missense mutation in the third exon of the Toll-like receptor-4 gene (Tlr4), predicted to replace proline with histidine at position 712 of the polypeptide chain. C57BL/10ScCr mice are homozygous for a null mutation of Tlr4. Thus, the mammalian Tlr4 protein has been adapted primarily to subserve the recognition of LPS and presumably transduces the LPS signal across the plasma membrane. Destructive mutations of Tlr4 predispose to the development of Gram-negative sepsis, leaving most aspects of immune function intact.

http://science.sciencemag.org/content/sci/282/5396/2085.full.pdf

Defective LPS Signaling in C3H/HeJ and C57BL/10ScCr Mice: Mutations in Tlr4 Gene

Defective LPS signaling in C3 H/HeJ and C57 BL/10 ScCr mice: Mutations in Tlr4 Gene

Diabetes and obesity are two metabolic diseases characterized by insulin resistance and a low-grade inflammation. Seeking an inflammatory factor causative of the onset of insulin resistance, obesity, and diabetes, we have identified bacterial lipopolysaccharide (LPS) as a triggering factor. We found that normal endotoxemia increased or decreased during the fed or fasted state, respectively, on a nutritional basis and that a 4-week high-fat diet chronically increased plasma LPS concentration two to three times, a threshold that we have defined as metabolic endotoxemia. Importantly, a high-fat diet increased the proportion of an LPS-containing microbiota in the gut. When metabolic endotoxemia was induced for 4 weeks in mice through continuous subcutaneous infusion of LPS, fasted glycemia and insulinemia and whole-body, liver, and adipose tissue weight gain were increased to a similar extent as in high-fat-fed mice. In addition, adipose tissue F4/80-positive cells and markers of inflammation, and liver triglyceride content, were increased. Furthermore, liver, but not whole-body, insulin resistance was detected in LPS-infused mice. CD14 mutant mice resisted most of the LPS and high-fat diet-induced features of metabolic diseases. This new finding demonstrates that metabolic endotoxemia dysregulates the inflammatory tone and triggers body weight gain and diabetes. We conclude that the LPS/CD14 system sets the tone of insulin sensitivity and the onset of diabetes and obesity. Lowering plasma LPS concentration could be a potent strategy for the control of metabolic diseases.

/pdf/metabolic-endotoxemia-initiates-obesity-and-insulin-4xi3cellv2.pdf

Metabolic endotoxemia initiates obesity and insulin resistance

Toll-like receptors have a crucial role in the detection of microbial infection in mammals and insects. In mammals, these receptors have evolved to recognize conserved products unique to microbial metabolism. This specificity allows the Toll proteins to detect the presence of infection and to induce activation of inflammatory and antimicrobial innate immune responses. Recognition of microbial products by Toll-like receptors expressed on dendritic cells triggers functional maturation of dendritic cells and leads to initiation of antigen-specific adaptive immune responses.

/pdf/toll-like-receptors-and-innate-immunity-5783s8xir7.pdf

Toll-like receptors and innate immunity

Resistance to Endotoxin Shock and Reduced Dissemination of Gram-Negative Bacteria in CD14-Deficient Mice

CD14 is a myeloid differentiation Ag expressed primarily on peripheral blood monocytes and macrophages. Although its function is unknown, the CD14 gene maps to a region encoding several myeloid growth factors and receptors. Analysis of the CD14 protein sequence deduced from the cDNA shows that although the CD14 protein contains a characteristic leader peptide, it lacks a characteristic transmembrane region, suggesting that CD14 may be anchored to the membrane via glycosylphosphatidylinositol (PI). Treatment of monocytes as well as a CD14-expressing neuroglioma cell line with PI-phospholipase C removed CD14 from the cell surface. Furthermore, monocytes from a patient with paroxysmal nocturnal hemoglobinuria, a disease characterized by lack of expression of other PI-linked proteins, failed to express CD14. Interestingly, the CD14-expressing neuroglioma cell line, which had been transfected with a single CD14 cDNA, released a soluble form of CD14 into the supernatant. Soluble forms of CD14 have previously been observed in serum of normal individuals and in culture supernatants of CD14+ cells. Biosynthetic experiments reveal that this soluble form of CD14 (48 kDa), which is smaller than the form released from the membrane by PI-phospholipase C (53 kDa), does not contain ethanolamine, the first constitutent of the PI-anchoring system. These studies demonstrate that CD14 is a member of the family of PI-anchored proteins and suggest that soluble forms of CD14 represent molecules that completely lack the PI-anchoring system.

The monocyte differentiation antigen, CD14, is anchored to the cell membrane by a phosphatidylinositol linkage.

CD14 is a myelomonocytic differentiation antigen expressed by monocytes, macrophages, and activated granulocytes and is detectable with the monoclonal antibodies MO2, MY4, and LeuM3. Analyses of complementary DNA and genomic clones of CD14 show that it has a novel structure and that it maps to chromosome 5 within a region containing other genes encoding growth factors and receptors; it may therefore represent a new receptor important for myeloid differentiation. In addition, the CD14 gene is included in the "critical" region that is frequently deleted in certain myeloid leukemias.

https://science.sciencemag.org/content/sci/239/4839/497.full.pdf

The CD14 monocyte differentiation antigen maps to a region encoding growth factors and receptors

In vitro studies have previously shown that the myelomonocytic differentiation antigen CD14 is a receptor for a complex consisting of lipopolysaccharide (LPS) and LPS-binding protein. To investigate the role of CD14 in vivo and its relationship to induction of LPS-induced endotoxin shock, transgenic mice expressing human CD14 were produced. These mice express human CD14 strongly on the surface of their monocytes, neutrophils, and Thy-1(+) lymphocytes and are hypersensitive to LPS, as evidenced by their increased susceptibility to endotoxin shock. These results document the importance of CD14 in vivo as a primary mediator of this lethal syndrome. Furthermore, these mice provide an important model for testing the therapeutic effects of agents directed specifically against the human, as opposed to the murine, CD14 protein in preventing LPS-induced endotoxin shock.

https://www.pnas.org/content/pnas/90/6/2380.full.pdf

Transgenic mice expressing human CD14 are hypersensitive to lipopolysaccharide.

Six monoclonal antibodies (MAb) which react with myelomonocytic cells representing various stages of differentiation, and which precipitate six different cell surface molecules, were identified. A 50 to 55 kilodalton (Kd) glycoprotein, restricted in expression to mature cells of the monocyte lineage, was detected by immunoprecipitation with antibody MoS39. By using COS-7 cells transfected with a cDNA clone encoding the MoS39 antigen, various well-described anti-monocyte MAb, including Mo2, My4, Leu-M3 (MoP9), MoP15, MoS1, and 63D3, also bound to MoS39-expressing COS-7 cells, suggesting that this group of antibodies reacted with the same glycoprotein. Immature cells of the myelomonocytic lineage were shown to express two distinct molecules: one with an m.w. of 26 to 28 Kd identified by antibody SG133, and the second, a 130 to 140 Kd glycoprotein identified by MoU26. Mature granulocytes were found to express a 60 Kd molecule identified by antibody SG185 which was absent from other cells of this lineage. Two other molecules were shown to be present on both mature and immature cells of the granulocytic and monocytic lineages: a 130 to 140 Kd glycoprotein identified by antibody SG134, and a 160 to 170 Kd glycoprotein recognized by antibody MoU48.

Enza Ferrero

Papers

Resistance to Endotoxin Shock and Reduced Dissemination of Gram-Negative Bacteria in CD14-Deficient Mice

The monocyte differentiation antigen, CD14, is anchored to the cell membrane by a phosphatidylinositol linkage.

The CD14 monocyte differentiation antigen maps to a region encoding growth factors and receptors

Transgenic mice expressing human CD14 are hypersensitive to lipopolysaccharide.

Biochemistry and expression of myelomonocytic antigens.