= Endotoxin
<Endotoxin> is bacterial <lipopolysaccharide> associated with the <bacterial outer membrane> of <Gram-negative bacteria>. Its ability to provoke a host response is distinct from the ability of a living <bacterium> to multiply. Detecting an endotoxin-related response and detecting a replicating <infection> therefore answer different questions.<Bacterial Endotoxins Pyrogens by the Food and Drug Administration>[Inspection Technical Guide 40, 20 March 1985; Characteristics of Bacterial Endotoxin]{ref}
An illuminating genetic experiment connected this response to a host recognition pathway. In 1998, <A. Poltorak> and colleagues examined two mouse strains with weak <lipopolysaccharide> signaling. One carried a missense <mutation> in the gene encoding <Toll-like receptor 4>; the other carried a null mutation of that gene. Independent disruptions converging on the same component supplied evidence for its role in the response.<Defective LPS signaling in C3H HeJ and C57BL 10ScCr mice: mutations in Tlr4 gene by A. Poltorak and others>[Science 282, 2085–2088, Abstract: missense and null Tlr4 mutations]{ref}
The reported animals were relatively resistant to endotoxin effects but susceptible to infection with <Gram-negative bacteria>. A reduced response to a bacterial component did not amount to improved defence against the living <organism>. This distinction connects molecular recognition to the protective function of <innate immunity>, rather than treating every inflammatory response as an independent measure of pathogen abundance.<Defective LPS signaling in C3H HeJ and C57BL 10ScCr mice: mutations in Tlr4 gene by A. Poltorak and others>[Abstract, contrasting endotoxin resistance and susceptibility to infection]{ref}
The genetic result establishes a requirement in a signaling pathway under the studied conditions. By itself it does not reveal every physical contact made by the <receptor> or show that a measured host response depends only on how much <lipopolysaccharide> is present. Ligand identity, host <genotype> and the measured endpoint are separate parts of the explanation.
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