Abstract
Undoubtedly, mast cells take part in host defense against microorganisms as they are numerous at the portal of infection, they release many proinflammatory and antimicrobial mediators, and they express pattern recognition receptors, such as TLRs. These receptors play a key role in recognition and binding molecules associated with microorganisms and molecules associated with damage. Cathelicidins exhibit direct antimicrobial activities against a broad spectrum of microbes by perturbing their cell membranes. Accumulating evidence suggests a role for these molecules in supporting cell activation. We examined the impact of human cathelicidin LL-37 on tissue mast cell TLR expression and distribution. Depending on context, we show that LL-37 stimulation resulted in minor to major effects on TLR2, TLR3, TLR4, TLR5, TLR7, and TLR9 expression. Confocal microscopy analysis showed that, upon stimulation, TLRs may translocate from the cell interior to the surface and conversely. FPR2 and EGFR inhibitors reduced the increase in expression of selected receptors. We also established that LL-37 acts as a powerful inducer of CCL3 and ROS generation. These results showed that in response to LL-37, mast cells enhance the capability to detect invading pathogens by modulation of TLR expression in what may be involved FPR2 or EGFR molecules.
Highlights
Cathelicidins, the family of highly diverse antimicrobial peptides, are found in many mammalian species including rabbits, horses, pigs, rats, monkeys, cattle, and humans
We first examined the expression of TLR mRNAs by mature rat mast cells in response to LL-37
1 h stimulation with LL-37 caused an increase in TLR5 mRNA expression (Figure 1(d)), and the expression of TLR7 mRNA was significantly higher at 3 and 6 h (Figure 1(e))
Summary
Cathelicidins, the family of highly diverse antimicrobial peptides, are found in many mammalian species including rabbits, horses, pigs, rats, monkeys, cattle, and humans. These natural antibiotics are composed of 12–50 amino acid residues, and their molecular weight are in the range of 3 to 10 kDa. Peptides from the cathelicidin family have α-helix structure and are produced by neutrophils, endothelial cells, keratinocytes, macrophages, mast cells, NK cells, dendritic cells, and lymphocytes [1, 2]. Only one cathelicidin leucine-leucine-37 (LL-37) formed from the precursor protein hCAP18, is expressed. Apart from direct interaction with microbes, human cathelicidin can exert
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