Abstract
Antimicrobial peptides that contribute to innate immunity are among the most important protective measures against infection in many organisms. Several substances are known to regulate the expression of antimicrobial peptides. In this study, we investigated the factors in lactic acid bacteria (LAB) that induce antimicrobial peptide expression in the host. We found that Lactobacillus helveticus SBT2171 (LH2171) induced the expression of human β-defensin (hBD)2 in Caco-2 human colonic epithelial cells. Specifically, surface layer protein (SLP) of LH2171 stimulated hBD2 expression by activating c-Jun N-terminal kinase (JNK) signaling via Toll-like receptor (TLR)2 in Caco-2 cells. SLPs extracted from other lactobacilli similarly increased hBD2 expression, suggesting that this stimulatory effect is common feature of Lactobacillus SLPs. Interestingly, Lactobacillus strains that strongly induced hBD2 expression also potently activated JNK signaling. Thus, upregulation of hBD2 induced by TLR2–JNK signaling contributes to protection of the host against infection.
Highlights
Organisms are constantly exposed to infectious agents in the environment
We found that surface layer protein (SLP) increased hBD2 expression to a greater extent than Lactobacillus helveticus SBT2171 (LH2171) bacterial cell (Figure 1A)
We found that Jun N-terminal kinase (JNK) inhibition by SP600125 abolished the increase in hBD2 induced by LH2171 SLP, whereas the p38 mitogen-activated protein kinase (MAPK) inhibitor SB202190 and extracellular signal-regulated kinase (ERK) inhibitor PD-98059 did not have this effect
Summary
Organisms are constantly exposed to infectious agents in the environment. To protect against infection, organisms have evolved defense strategies including immune responses. The innate immune system rapidly and non- eliminates foreign substances such as pathogens from the body and is considered as the first line of host defense. This system comprises cellular and humoral components; the latter includes antimicrobial peptides, which are found in mammals, amphibians, and insects and exert bactericidal effects mainly by directly interacting with target bacteria and perturbing cell membrane function (Diamond et al, 2008).
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