Suttichai Krisanaprakornkit and Sakornrat Khongkhunthian
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neutrophils, which are abundant in diseased tissues, are sufficient to exert the chemotactic
effect. Moreover, LL-37 attracts migration of mast cells in rats (Niyonsaba et al, 2002a) and
induces histamine release from mast cell granules via intracellular calcium mobilization
(Niyonsaba et al, 2001), leading to enhanced phagocytosis of opsonized microorganisms. LL-
37 can also induce dendritic cell differentiation, which then activates cell-mediated acquired
immunity through a Th1 profile (Davidson et al, 2004).
Several studies have also shown the inducible effect of LL-37 on the expression of
several immune-related genes. For instance, LL-37 can induce expression of chemokines and
chemokine receptors (Scott et al, 2002) via MAP kinase pathways (Bowdish et al, 2004). It
can also induce expression of intercellular adhesion molecule-1 (Edfeldt et al, 2006),
implying an indirect role for LL-37 in chemotaxis in addition to its direct role, as indicated
above.LL-37 transactivates an epidermal growth factor receptor (EGFR) through induction of
matrix metalloproteinase activity, resulting in interleukin-8 (IL-8)
up-regulation and increased
cell proliferation in human bronchial epithelial cells (Tjabringa et al, 2003). Similarly, LL-37
enhances IL-8 expression and release by human airway smooth muscle cells, albeit through
purinergic receptors (Zuyderduyn et al, 2006). In addition, in the presence of IL-1
, lower
LL-37 concentrations can synergistically induce IL-8 synthesis in both human keratinocytes
and bronchial epithelial cells (Filewod et al, 2009), and up-regulate expression of IL-6, IL-10,
MCP-1, and MCP-3 in peripheral blood mononuclear cells (Yu et al, 2007).
With respect to periodontal cells, we have recently found similar IL-8 mRNA up-
regulation by LL-37 in both gingival epithelial cells and gingival fibroblasts in dose- and
time-dependent manners (Figure 1). Interestingly, the kinetics of IL-8 up-regulation between
these two cell types shows distinct profiles, indicating different signaling pathways
controlling IL-8 expression (Figure 1). Therefore, it is possible that LL-37 may
be responsible
for controlling neutrophil transmigration from blood vessels into diseased periodontal tissue
in chronic periodontitis.
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