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

Leukocytes respond to lipopolysaccharide (LPS) at nanogram per milliliter concentrations with secretion of cytokines such as tumor necrosis factor-alpha (TNF-alpha). Excess secretion of TNF-alpha causes endotoxic shock, an often fatal complication of infection. LPS in the bloodstream rapidly binds to the serum protein, lipopolysaccharide binding protein (LBP), and cellular responses to physiological levels of LPS are dependent on LBP. CD14, a differentiation antigen of monocytes, was found to bind complexes of LPS and LBP, and blockade of CD14 with monoclonal antibodies prevented synthesis of TNF-alpha by whole blood incubated with LPS. Thus, LPS may induce responses by interacting with a soluble binding protein in serum that then binds the cell surface protein CD14.

https://science.sciencemag.org/content/sci/249/4975/1431.full.pdf

CD14, a receptor for complexes of lipopolysaccharide (LPS) and LPS binding protein.

The innate immune response is the first line of defence against infectious disease. The principal challenge for the host is to detect the pathogen and mount a rapid defensive response. A group of proteins that comprise the Toll or Toll-like family of receptors perform this role in vertebrate and invertebrate organisms. This reflects a remarkable conservation of function and it is therefore not surprising that studies of the mechanism by which they act has revealed new and important insights into host defence.

Toll-like receptors in the induction of the innate immune response

LPS induction of gene expression in human monocytes

The primary structure of lipopolysaccharide binding protein (LBP), a trace plasma protein that binds to the lipid A moiety of bacterial lipopolysaccharides (LPSs), was deduced by sequencing cloned complementary DNA. LBP shares sequence identity with another LPS binding protein found in granulocytes, bactericidal/permeability-increasing protein, and with cholesterol ester transport protein of the plasma. LBP may control the response to LPS under physiologic conditions by forming high-affinity complexes with LPS that bind to monocytes and macrophages, which then secrete tumor necrosis factor. The identification of this pathway for LPS-induced monocyte stimulation may aid in the development of treatments for diseases in which Gram-negative sepsis or endotoxemia are involved.

https://science.sciencemag.org/content/sci/249/4975/1429.full.pdf

Structure and function of lipopolysaccharide binding protein

Cloning of the cDNA of a human neutrophil bactericidal protein. Structural and functional correlations.

Complete mutagenesis of the extracellular domain of interleukin-8 (IL-8) type A receptor identifies charged residues mediating IL-8 binding and signal transduction.

Mutational analysis of the intracellular domain of the human growth hormone receptor.

Humanized anti-IL-8 monoclonal antibodies and variants thereof are described for use in diagnostic applications and in the treatment of inflammatory disorders. Also described is a conjugate formed by an antibody fragment covalently attached to a non-proteinaceous polymer, wherein the apparent size of the conjugate is at least about 500 kD. The conjugate exhibits substantially improved half-life, mean residence time, and/or clearance rate in circulation as compared to the underivatized parental antibody fragment.

Steven R. Leong

Papers

Structure and function of lipopolysaccharide binding protein

Cloning of the cDNA of a human neutrophil bactericidal protein. Structural and functional correlations.

Complete mutagenesis of the extracellular domain of interleukin-8 (IL-8) type A receptor identifies charged residues mediating IL-8 binding and signal transduction.

Mutational analysis of the intracellular domain of the human growth hormone receptor.

Humanized anti-IL-8 monoclonal antibodies