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INTRODUCTION: Vitamin D deficiency has been proposed to confer susceptibility to acquiring tuberculosis infection by impairing the innate immune response. METHODS: In an exploratory study, we examined whether the levels of 25-hydroxyvitamin D3 (25(OH)D3) in serum, and cathelicidin - an antimicrobial peptide-induced under calcitriol - in the nasal fluid, would associate with the risk of acquiring tuberculosis infection. RESULTS: Within a prospective cohort of 231 tuberculosis household contacts tested with repeated interferon-gamma release assays, we serially analyzed all the uninfected contacts acquiring tuberculosis infection at follow-up ("converters", n=18), and an age and sex-matched control group of contacts not acquiring tuberculosis infection ("non-converters", n=36). The median levels of serum 25(OH)D3 did not differ between convertors and non-converters at baseline (14.9 vs. 13.2 ng/ml, p=0.41), nor at follow-up (19.0 vs 18.6ng/ml, p=0.83). Similarly, cathelicidin levels did not differ between both groups. CONCLUSION: These data argue against a major role for hypovitaminosis D in tuberculosis infection susceptibility.

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Among the various biological properties presented by Mesenchymal Stem Cells (MSCs), their ability to control the immune response and fight pathogen infection through the production of antimicrobial peptides (AMPs) have been the subject of intense research in recent years. AMPs secreted by MSCs exhibit activity against a wide range of microorganisms, including bacteria, fungi, yeasts, and viruses. The main AMPs produced by these cells are hepcidin, cathelicidin LL-37, and ß-defensin-2. In addition to acting against pathogens, those AMPs have also been shown to interact with MSCs to modulate MSC proliferation, migration, and regeneration, indicating that such peptides exert a more diverse biological effect than initially thought. In the present review, we discuss the production of AMPs by MSCs, revise the multiple functions of these peptides, including their influence over MSCs, and present an overview of clinical situations in which the antimicrobial properties of MSCs may be explored for therapy. Finally, we discuss possibilities of combining MSCs and AMPs to generate improved therapeutic strategies.

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An increased resistance to surgical site infections has been associated with surgical meshes composed of naturally occurring materials, including poly-4-hydroxybutrate (4HB). 4HB is a naturally occurring short-chain fatty acid that has been shown to promote endogenous expression of the Cramp gene coding for the antimicrobial peptide (AMP) cathelicidin LL-37 in murine bone marrow-derived macrophages. The molecular pathways involved in the 4HB-induced cathelicidin LL-37 expression have not yet been identified. The present study showed that transcriptional activation of the Cramp gene by 4HB is independent of inhibition of histone deacetylase (HDAC) activity, and that upregulation of Cramp is modulated by the G-protein coupled receptor GPR109A. Furthermore, an intracellular signaling cascade that promotes the activation of the MAP kinases, p38 and JNK, and a subsequent NF-κB phosphorylation downstream from p38 is essential for the AMP transcriptional response in 4HB-stimulated macrophages. The findings provide a solid scientific basis and rationale for the decreased incidence of surgical site infections with the use of this type of surgical meshes. Further clinical significance is found in the fact that the 4HB activated molecular pathway includes common targets of frequently used nonsteroidal anti-inflammatory drugs (NSAIDs) and other FDA approved drugs recognizing G-protein coupled receptors.

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Cardiolipin is an anionic tetra-acyl chained glycerophospholipid that increases lipid packing levels and induces intrinsic negative curvature in membranes. Cardiolipin is found in Staphylococcus aureus (S. aureus) membranes, where increased levels of this lipid are induced at the expense of diacyl phosphatidylglycerol in response to stress. We investigate cardiolipin as an inhibitor of the lytic activity of the cationic antimicrobial peptides LL-37 and ∆M2 in model systems with varying phosphatidylglycerol/cardiolipin ratios. Using HPTLC, we show that S. aureus (RN4220), under different growth conditions, has a phosphatidylglycerol/cardiolipin ratio of 80:20. From this, we chose three model systems to evaluate (100:0, 80:20, 60:40). ∆M2 presents higher binding affinity towards all mixtures compared to LL-37. This correlates with the higher antimicrobial activity of ∆M2 compared to LL-37 in S. aureus (MIC90 of 14 µM for ∆M2 and 57.7 µM for LL-37). Laurdan GP shows that Cardiolipin decreases lipid headgroup spacing. We find that cardiolipin does not affect ∆M2 or LL-37 binding to phosphatidylglycerol/cardiolipin liposomes. Instead, cardiolipin inhibits the ability of both peptides to induce calcein leakage in model liposomes. In conclusion, cardiolipin can reduce cAMP activity by inhibiting lysis but not binding.

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OBJECTIVE: Controversies exist regarding the relationship between the concentrations of antimicrobial peptides (AMPs) and presence of dental caries in children. Thus, the aim of this study was to examine levels of AMPs in saliva of caries-free (CF), early childhood caries (ECC) and severe early childhood caries (S-ECC) children to determine if the levels of these salivary peptides individually or in combinations were related to caries severity and mutans streptococci levels. DESIGN: 36 to 60 month-old children were selected to participate in this study. Children were grouped into CF group (n=29), ECC group (n=25) and S-ECC group (n=29). Saliva was collected from children for microbiological analysis by culture. Salivary concentrations of cathelicidin LL-37, human ß-defensin 2 (hBD-2), human ß-defensin 3 (hBD-3) and histatin-5 (HTN-5) were determined by ELISA. RESULTS: Salivary concentrations of AMPs did not differ among CF, ECC and S-ECC groups. Data showed positive correlations between mutans streptococci levels and salivary hBD-2 or HTN-5. Positive correlations were found between hBD-2, hBD-3, LL-37 and HTN-5. Combinations among AMPs, mainly LL-37, were positively associated with caries levels. CONCLUSIONS: Salivary concentrations of AMPs individually were not associated with the severity of early childhood caries. The stimulus of caries appears to trigger a biological response, however, with a combination of these peptides.

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