Background — Innate immune reactions against bacteria and viruses have been implicated in the pathogenesis of atherosclerosis. To explore the molecular mechanism by which microbe recognition occurs in the artery wall, we characterized the expression of toll-like receptors (TLRs), a family of pathogen pattern recognition receptors, in atherosclerotic lesions. Methods and Results — Semiquantitative polymerase chain reaction and immunohistochemical analysis demonstrated that of 9 TLRs, the expression of TLR1, TLR2, and TLR4 was markedly enhanced in human atherosclerotic plaques. A considerable proportion of TLR-expressing cells were also activated, as shown by the nuclear translocation of nuclear factor-κB. Conclusion — Our findings illustrate a repertoire of TLRs associated with inflammatory activation in human atherosclerotic lesions, and they encourage further exploration of innate immunity in the pathogenesis of atherosclerosis.

We investigated the mechanisms by which T-cell cytokines are able to influence the Toll-like receptor (TLR)-induced, vitamin Ddependent antimicrobial pathway in human monocytes. T-cell cytokines differentially influenced TLR2/1-induced expression of the antimicrobial peptides cathelicidin and DEFB4, being upregulated by IFN-γ, down-regulated by IL-4, and unaffected by IL-17. The Th1 cytokine IFN-γ up-regulated TLR2/1 induction of 25-hydroxyvitamin D-1α-hydroxylase (i.e., CYP27B1), leading to enhanced bioconversion of 25-hydroxyvitamin D 3 (25D 3 ) to its active metabolite 1,25D 3 . In contrast, the Th2 cytokine IL-4, by itself and in combination with the TLR2/1 ligand, induced catabolism of 25D 3 to the inactive metabolite 24,25D 3 , and was dependent on expression of vitamin D-24-hydroxylase (i.e., CYP24A1). Therefore, the ability of T-cell cytokines to differentially control monocyte vitamin D metabolism represents a mechanism by which cell-mediated immune responses can regulate innate immune mechanisms to defend against microbial pathogens. Mycobacterium tuberculosisT he ability of Toll-like receptors (TLRs) to trigger a direct antimicrobial activity is a key aspect of their role in innate immunity. In mouse monocytes, activation of the TLR2/1 heterodimer by microbial lipoproteins (1-3), induces an antimicrobial activity against Mycobacterium tuberculosis that is nitric oxide (NO)-dependent, but in human monocytes is NO-independent (4). Instead, a key antimicrobial mechanism for TLR-activated human monocytes involves induction of the 25-hydroxyvitamin D-1α-hydroxylase (i.e., CYP27B1), which enzymatically converts the major circulating form of vitamin D, 25-hydroxyvitamin D3 (25D 3 ) into the active form of vitamin D, 1,25D 3 . Parallel TLRmediated up-regulation of the vitamin D receptor (VDR) and activation of this receptor by 1,25D 3 leads to downstream induction of the genes encoding the antimicrobial peptides cathelicidin and DEFB4 (5-10). Here, we tested the hypothesis that adaptive T-cell cytokines, including key cytokines of the Th1, Th2, and Th17 pattern, regulate the TLR2/1-induced, vitamin Ddependent antimicrobial pathway. ResultsEffect of T-Cell Cytokines on TLR2/1 Induction of Cathelicidin and DEFB4. To determine the role of individual cytokines on the TLRtriggered vitamin D-dependent induction of antimicrobial peptides, monocytes were treated with TLR2/1L with or without a specific T-cell cytokine, and cathelicidin and DEFB4 mRNAs measured at 24 h. IFN-γ by itself up-regulated cathelicidin and DEFB4 mRNA levels by twofold ( Fig. 1A; P < 0.05 and P < 0.001). Consistent with previous findings, TLR2/1L induced both cathelicidin and DEFB4 mRNAs (8, 10). However, whereas IFN-γ augmented TLR2/1L-triggered induction of cathelicidin by 4.1-fold (P < 0.01), it had no effect on TLR2/1L-mediated induction of DEFB4 (Fig. 1A). The addition of IL-17 had no effect on induction of antimicrobial peptide gene expression in the presence or absence of TLR2/1L (Fig. 1B).Whereas IFN-γ augmented TLR2/1 induction of cath...

Leprosy provides a model to investigate mechanisms of immune regulation in humans, given that the disease forms a clinical-immunological spectrum. Here, we identified 13 miRNAs that were differentially expressed in the lesions of subjects with progressive lepromatous (L-lep) vs. the self-limited tuberculoid (T-lep) disease. Bioinformatic analysis revealed a significant enrichment of L-lep-specific miRNAs that preferentially target key immune genes downregulated in L-lep vs. T-lep lesions. The most differentially expressed miRNA in L-lep lesions, hsa-mir-21, was upregulated in M. leprae-infected monocytes. Hsa-mir-21, by downregulating toll-like receptor 2/1 (TLR2/1)-induced CYP27B1 and IL1B as well as upregulating IL-10, inhibited gene expression of the vitamin D-dependent antimicrobial peptides, CAMP and DEFB4A. Conversely, knockdown of hsa-mir-21 in M. leprae-infected monocytes enhanced expression of CAMP and DEFB4A and restored TLR2/1-mediated antimicrobial activity against M. leprae. Therefore, the ability of M. leprae to upregulate hsa-mir-21 targets multiple genes associated with the immunologically localized disease form, providing an effective mechanism to escape from the vitamin D-dependent antimicrobial pathway.

Objective-Antimicrobial peptides are effector molecules of the innate immune system. To understand the function of vascular innate immunity in atherosclerosis, we investigated the role of LL-37, a cathelicidin antimicrobial peptide, in the disease process. Methods and Results-Using real-time polymerase chain reaction, we found a 6-fold increase in human cationic antimicrobial protein 18/LL-37 transcript in human atherosclerotic lesions compared with normal arteries. Immunohistochemical analysis of atherosclerotic plaques showed that LL-37 was expressed mainly by macrophages and some endothelial cells. Western blot demonstrated existence of active LL-37 peptide and abundant proprotein in atheroma specimens. To understand the functional implication of LL-37 production in atherosclerosis, the transcription profile was assessed in endothelial cells treated with LL-37. Our data show that LL-37 induces expression of the adhesion molecule intercellular adhesion molecule-1 and the chemokine monocyte chemoattractant protein 1 in endothelial cells. Intriguingly, Chlamydia pneumoniae withstood the antimicrobial activity of LL-37 in vitro, although inflammatory response was induced on infection. Conclusion-LL-