Differential Expression of IL-1β, TNF-α, IL-6, and IL-8 in Human Monocytes in Response to Lipopolysaccharides from Different Microbes

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Abstract
Macrophages respond to bacterial lipopolysaccharides (LPS) and activate several host defense functions through production of mediators. However, it is not clear whether the degree of macrophage responsiveness to different sources of LPS is equivalent to or varies with the source of LPS. Therefore, in this report, we examined the extent of the human monocyte response to LPS derived from two oral pathogens, Actinobacillus actinomycetemcomitans (Aa) and Porphyromonas gingivalis (Pg). Additionally, due to its well-established ability to activate monocytes, we used LPS from Escherichia coli (Ec). Human monocytes, when activated with a specific source of LPS, exhibited rapid expression of mRNA for IL-1β, TNF-a, and IL-8, which was followed by IL-6, as measured by RNA-PCR. Moreover, the expression of mRNA for these cytokines was followed by cytokine synthesis. Monocytes from the same subject, when activated with LPS from Pg, Aa, or Ec expressed quantitatively different levels of mRNA and proteins for all four cytokines. A given LPS induced either high or low expression of the battery of cytokines tested, indicating that the expression of these pro-inflammatory cytokines may be regulated by a single or a cluster of gene(s). However, no apparent differences in the time course of mRNA expression for these cytokines were observed in response to any of the LPS tested. Furthermore, the relative ability of the different sources of LPS to induce mRNA for cytokines varied throughout a wide range of LPS concentrations. This suggests that differences exist in the sensitivity of monocytes to a specific LPS, rather than in the kinetics of the secretory process itself. The ability of LPS to induce cytokine-specific mRNA also depended on the source of monocytes. Our results demonstrate that monocyte activation and cytokine release depend on the physicochemical form of LPS as well as the source of monocytes. These critical determinants may be significant in the pathogenesis of periodontal infections.