Basic Knowledge of Lipopolysaccharide (LPS)

(10) LPS is diverse

The LPS that is well known is the LPS of gram-negative bacteria belonging to the class γ-Proteobacteria of the phylum Proteobacteria. Table 1 illustrates the classification of some of these gram-negative bacteria.

Bacteria are classified into phylum, class, order, family, genus, and species. Escherichia coli, Salmonella enterica, and Vibrio cholerae are commonly known bacteria that belong to the class γ-Proteobacteria of the phylum Proteobacteria. The biological functions of LPS are similar across most bacteria belonging to this group. That is, when applied to macrophages, they have an extremely high ability to induce the production of cytokines (both inflammatory and/or anti-inflammatory cytokines).

However, even within Proteobacteria, α-Proteobacteria such as Acetobacter aceti produce LPS with a different structure and with a reduced ability to induce cytokine production.

The periodontal disease-causing bacterium Porphyromonas gingivalis belongs to the phylum Bacteroidetes, which is genetically distant from Proteobacteria. The structure of LPS produced by Porphyromonas is extremely different; this LPS possesses almost no binding ability to TLR4 (LPS receptor) (* 1) and therefore has very limited ability to induce cytokine production. In fact, a recent study on bacteria causing periodontal disease has revealed that lipoproteins but not LPS bind to the TLR2 receptors to induce cytokine production (* 2).

Indeed, both Acetobacter LPS and Porphyromonas LPS are believed to possess physiological activities that cannot be measured by cytokine induction alone. Nevertheless, LPS is present in diverse forms. Moreover, LPS with high cytokine-inducing ability show different effects when administered into the body and when administered orally or transdermally. This phenomenon is explained elsewhere ((11)LPS exerts different effects between intrabody administration and oral/transdermal administration.).

（*1）Signaling by toll-like receptor 2 and 4 agonists results in differential gene expression in murine macrophages, Infection and Immunity 69 (3): 1477-1482 (2001)
（*2）Bacteroides類縁菌LPSの化学構造と免疫生物学的活性━Porphyromonas gingivalis LPS研究を中心に━, 日本細菌学雑誌61 (4): 391-404 (2006)