Cathelicidin and human β-defensin 2 in bronchoalveolar lavage fluid of children with pulmonary tuberculosis

The Levels of the Human-β-Defensin-2 and LL-37 in the Sputum of Children with Cystic Fibrosis: A Case–control Study and Literature Review

BACKGROUND: Cystic fibrosis (CF) is a genetic disorder with an autosomal-recessive type of inheritance. Based on their host-defending and pro-inflammatory functions, antimicrobial peptides (AMPs) likely have one of the central roles in the pathogenesis of lung disease in CF. AIM: The purpose of the study was to measure the concentration of AMPs in the sputum of children with CF and evaluate any correlation with a bacterial profile of the lungs. METHODS: Lung colonization was evaluated using a culture-dependent method, sputum was utilized. A sandwich-ELISA was used to measure hBD-2 and hCAP-18/LL-37 in the sputum. RESULTS: There were 27 children enrolled in the study group, median age of inclusion was 11.4 (8.5; 14.8) years old. The control group consisted of 14 children, 11.6 (8.6; 12.6) years old. The concentration of AMPs was not correlating with participants` age (rs = −0.286, p = 0.148 – defensin hDB-2; rs = −0.084, p = 0.676 – cathelicidin hCAP-18/LL-37). The concentration of hBD-2 was from 64.01 to 813.61 pg/mL. The concentration of hCAP-18/LL-37 was from 3.24 to 35.98 ng/mL. There were significant differences in the content of AMPs on respiratory samples between study and control group (U = 976.5, p = 0.001 – for hBD-2; U = 1080.5, p < 0.001). The correlation between current infection Pseudomonas aeruginosa and concentration of hBD-2 (rs = 0.167; p = 0.406) was not found. However, the presence of P. aeruginosa correlated with density of neutrophilic infiltration (rs = 0.622; p = 0.001). The concentration of hBD-2 showed direct medium correlation with total cells count (rs = 0.881, p < 0.001). Correlation between current infection P. aeruginosa and concentration of hCAP-18/LL-37 (rs = 0.788; p < 0.001) was observed. With increases in total cell count and relative neutrophils count, the concentration of hCAP-18/LL-37 was increased and the power of the association was medium (rs = 0.453; p = 0,018; rs = 0,592; p = 0,001). The correlation between concentrations of hBD-2 and hCAP-18/LL-37 (rs = 0.316, p > 0.1) was not found. CONCLUSIONS: Measured AMPs correlated with cellular inflammatory markers and, probably, their overexpression is dedicated to stimulating a cellular component of innate immune response; there was no correlation between bacterial colonization of lungs and levels of hBD-2, so our findings sustain that P. aeruginosa is a leading but non-single contributor to persistent local inflammation in polymicrobial lungs.

Antimicrobial Peptides in Early-Life Host Defense, Perinatal Infections, and Necrotizing Enterocolitis—An Update

Host defense against early-life infections such as chorioamnionitis, neonatal sepsis, or necrotizing enterocolitis (NEC) relies primarily on innate immunity, in which antimicrobial peptides (AMPs) play a major role. AMPs that are important for the fetus and neonate include α and β defensins, cathelicidin LL-37, antiproteases (elafin, SLPI), and hepcidin. They can be produced by the fetus or neonate, the placenta, chorioamniotic membranes, recruited neutrophils, and milk-protein ingestion or proteolysis. They possess antimicrobial, immunomodulating, inflammation-regulating, and tissue-repairing properties. AMPs are expressed as early as the 13th week and increase progressively through gestation. Limited studies are available on AMP expression and levels in the fetus and neonate. Nevertheless, existing evidence supports the role of AMPs in pathogenesis of chorioamnionitis, neonatal sepsis, and NEC, and their association with disease severity. This suggests a potential role of AMPs in diagnosis, prevention, prognosis, and treatment of sepsis and NEC. Herein, we present an overview of the antimicrobial and immunomodulating properties of human AMPs, their sources in the intrauterine environment, fetus, and neonate, and their changes during pre- and post-natal infections and NEC. We also discuss emerging data regarding the potential utility of AMPs in early-life infections, as diagnostic or predictive biomarkers and as therapeutic alternatives or adjuncts to antibiotic therapy considering the increase of antibiotic resistance in neonatal intensive care units.

An Association Between Serum Vitamin D Levels and Serum Cathelicidin Antimicrobial Peptide (CAMP) Levels Among Tuberculosis Patients in Comparison with Control Subjects

Objectives:

The objective of this study is to compare the serum vitamin D and serum cathelicidin antimicrobial peptide (CAMP) levels among tuberculosis patients and healthy subjects and to determine the association between serum vitamin D and cathelicidin in tuberculosis.

Materials and Methods:

This is a case-control study carried out at the pulmonary medicine and pediatrics departments of a tertiary care hospital in Chengalpattu. The study included 180 tuberculosis cases and 90 control subjects of both sexes between the age group of 1 to 80 years. Serum was used to estimate vitamin D and CAMP. The study was analyzed using SPSS version 21 (IBM Corp. Armonk, New York). The results were evaluated using the chi-square test at a 95% confidence interval, and P value <.05 was considered highly significant.

Results:

This study observed vitamin D deficiency, vitamin D insufficiency, and optimum vitamin D among 55%, 41%, and 3.89% tuberculosis cases, respectively. Similarly, vitamin D deficiency, vitamin D insufficiency, and optimum vitamin D were seen in 40%, 50%, and 10% healthy controls, respectively.

Conclusion:

This study found no association between serum vitamin D and serum CAMP levels in tuberculosis patients and healthy controls.

Cathelicidin levels in nasal secretions are associated with the severity of acute bronchiolitis

OBJECTIVE

To investigate the association of serum vitamin D and nasal secretion antimicrobial peptides (AMPs) levels with the severity of acute bronchiolitis.

STUDY DESIGN

We conducted a prospective single pediatric tertiary care center cohort study of inpatients aged 0-18 months with a first episode of acute bronchiolitis from November 1st 2014 to April 30th 2017. Disease severity was determined by the length of hospitalization and supplemental hospital data. Qualitative measurements included serum 25(OH)D and nasal secretion LL-37 and β-defensin-2 levels. Correlations were examined with the Mann-Whitney and Kruskal-Wallis criteria for qualitative and the correlation coefficient Spearman's rho for quantitative factors. Multiple linear and logarithmic regression were performed to adjust for confounding factors.

RESULTS

The study population consisted of 153 infants and toddlers with median age 3.1 months (interquartile range:1.6-4.9). No association was found between serum 25(OH)D and AMPs nasal secretions levels. Serum 25(OH)D and nasal secretion β-defensin-2 levels were not associated with the severity of bronchiolitis. In contrast, LL-37 levels were inversely associated with the length of hospitalization (rho = -0.340, p = .001), the need for medication use (p = .001), as well as the duration of oxygen supplementation (rho = -0.339, p = .001), and intravenous fluid administration (rho = -0.323, p = .001). This association remained significant after adjustment for potential confounders.

CONCLUSION

A significant association between LL-37 nasal secretions levels with the severity of acute bronchiolitis was found in hospitalized infants and toddlers. The role of LL-37 in the pathogenesis of bronchiolitis merits further investigation.

Significance of the chemokine CXCL10 and human beta-defensin-3 as biomarkers of pulmonary tuberculosis

The biomarker significance of IL-35, chemokines (CXCL9 and CXCL10) and human beta-defensins (hBD2 and hBD3) was determined in pulmonary tuberculosis (TB) of 105 Iraqi patients; 37 had active disease, 41 had multi-drug resistant (MDR) PTB and 27 had a relapse of TB. A control sample of 79 healthy persons was also included. Serum levels of markers were assessed using enzyme-linked immunosorbent assay kits. Kruskal-Wallis test together with Dunn-Bonferroni post hoc test revealed significance differences between patients and controls in levels of IL-35, CXCL9, CXCL10 and hBD3, while hBD2 showed no significant difference. Receiver operating characteristic analysis demonstrated that CXCL10 and hBD3 were the most significant markers in predicting TB, particularly active disease. Logistic regression analysis proposed the susceptibility role of CXCL10 in TB. Gender- and age-dependent variations were also observed. Spearman's rank correlation analysis showed different correlations between markers in each group of patients and controls. In conclusion, CXCL10 was up-regulated in serum of TB patients, while hBD3 showed down-regulated level. Both serum proteins are possible candidate biomarkers for evaluation of TB progression, particularly in active disease.

Evidence that changes in antimicrobial peptides during tuberculosis are related to disease severity, clinical presentation, specific therapy and levels of immune-endocrine mediators

Given the role of host defense peptides (HDPs) in the defensive response against mycobacteria, we analyzed the circulating levels of LL-37, β-defensin-2 and -3 in newly diagnosed patients with pulmonary (PTB) or pleural tuberculosis (PLTB) in whom measurements of pleural fluids were also performed. Severe PTB patients displayed higher circulating amounts of β-defensin-3, statistically different from controls, further decreasing upon antimycobacterial treatment. LL-37 concentrations appeared within the normal range at diagnosis, but tended to increase during treatment, becoming statistically upon its completion in moderate cases. PLTB patients revealed decreased levels of β-defensin-2 in presence of increased amounts of β-defensin-3 and LL-37; in their plasma or pleural fluids. Considering the immune-endocrine dysregulation of tuberculosis, we also performed correlation analysis detecting positive associations between levels of cortisol, IL-6 and β-defensin-3 in plasma from untreated severe patients as did their dehydroepiandrosterone and LL-37 values. Increased presence of β-defensins, may represent an attempt to improve defensive mechanisms; which also take part in the inflammatory reaction accompanying TB, reinforced by the association with immune-endocrine mediators. The divergent profile of PLTB patients, decreased β-defensin-2 but increased β-defensin-3 and LL-37 levels, suggests a differential role of these HDPs in a situation characterized for its better protective response.

Serum concentrations of antimicrobial peptide cathelicidin LL-37 in patients with bacterial lung infections

Nowadays, data indicate that antimicrobial peptides play an important role in immunological defense. Human cathelicidin LL-37 possesses a broad spectrum of antimicrobial properties against Gram-positive and Gram-negative bacteria, and is thereby an important component of defense mechanisms within the respiratory tract. In this study, we determined the LL-37 serum level in patients with pneumonia caused by different bacteria species in comparison with healthy subjects. Twenty-two patients with pneumonia caused by coccal Gram-positive bacteria (I), 16 patients with pneumonia caused by Haemophilus influenzae (II), 29 patients with pneumonia caused by members of the Enterobacteriaceae (III), 13 patients caused by non-fermenting Gram-negative bacteria (IV), and 30 healthy controls were enrolled in the study. Serum LL-37 concentration was measured using an enzyme-linked immunosorbent assay (ELISA). The mean LL-37 concentration in pneumonia patients was significantly higher in group I (p = 0.0032), group II (p = 0.0022), and group III (p = 0.019), and significantly lower in group IV (p = 0.000004) as compared with healthy volunteers. Our data suggest that LL-37 plays an important role in defense mechanisms during pneumonia. The reduced level of this peptide in subjects with pneumonia caused by opportunistic bacteria may reflect weakened immune system reactivity in these patients.

Association between Mycobacterium avium complex lung disease and serum vitamin D status, antimicrobial peptide levels, and bone mineral density

Vitamin D maintains calcium balance and has immunomodulatory effects. Only few studies have revealed the relationship between vitamin D and its associated factors in Mycobacterium avium complex (MAC) infection. This study aimed to investigate the effects of MAC infection on serum vitamin D, human cationic antimicrobial protein 18, its C-terminal 37 amino acid fragment (hCAP18/LL-37) levels, and bone mineral density (BMD).We enrolled 58 patients with MAC lung disease and 15 control participants. Serum 25-hydroxyvitamin D and hCAP18/LL-37 levels were measured via enzyme-linked immunosorbent assay. Lastly, computed tomography scan density readings of the BMD of the thoracic and lumbar vertebral bones (Th4, Th7, Th10, and L1) were assessed.No significant differences in patient characteristics and serum vitamin D levels were observed. Patients with MAC lung disease had significantly low serum hCAP18/LL-37 levels (P = .049). Moreover, low BMD of the mean thoracic and lumbar vertebrae was observed (mean Th, P = .012; L1, P = .48, respectively). A higher prevalence of scoliosis (P = .031) was observed in the participants with low BMD compared with the control participants. Based on a multivariate analysis, patients with MAC lung disease had significantly lower body mass index [odds ratio (OR), 19.1; 95% confidence interval (CI), 2.0-419.0; P < .01] and vertebral BMD (OR, 12.4; 95% CI, 1.7-160.6; P = .012) than control participants.Serum hCAP18/LL-37 level and BMD were significantly decreased in patients with MAC lung disease without relation to serum vitamin D level. The vitamin D-independent pathway might affect the waning of antimicrobial peptides and decrease in BMD.

The association between vitamin D status and tuberculosis in children: A meta-analysis

BACKGROUND

Vitamin D deficiency (VDD) has been implicated in the pathogenesis of tuberculosis (TB), but most studies have not reported a significant association. We conducted a meta-analysis to explore the association between vitamin D status and TB in children.

METHODS

Web of Science, Ovid Medline, and EMBASE were searched for studies in English that discussed vitamin D status and TB in children before January 22, 2018.

RESULTS

From the 585 initially identified studies, we selected those that addressed an association between vitamin D status and TB according to our preselected inclusion criteria. Our meta-analysis included 10 studies. According to the random effects model, TB was significantly associated with VDD (ORs, 1.70; 95% CI, 1.20-2.42; P < .05) in children. Vitamin D levels were significantly lower in TB patients than in controls, with a mean difference d = -5.49 nmol/L (95% CI, -10.42 to -0.55; P < .05), indicating that VDD was significantly associated with TB (OR, 1.78; 95% CI, 1.30-2.44; P < .05) in children.

CONCLUSION

This study suggests that vitamin D levels are significantly lower in children with TB/latent TB infection than in controls. TB may contribute to VDD in children. Therefore, VDD may be associated with TB in children.

Body composition does not affect serum levels of cathelicidin LL-37 in elderly women with unipolar depression

OBJECTIVES

Antimicrobial peptides are components of the innate immune system. Cathelicidin LL-37 plays an important role in antimicrobial defense, exerts proinflammatory effect and strongly affects the immune system functioning. Our recent study revealed that serum concentration of LL-37 is increased in elderly women with depression. The aim of this study is to evaluate serum LL-37 levels in elderly women with depression and to compare them with non-depressed elderly women, matched for anthropometric and body composition parameters.

METHODS

Forty women with unipolar depression and 23 non-depressed women (age ≥60 years) were included into the study. Anthropometric measurements and biochemical analyzes were performed. Concentration of LL-37 in serum was assessed using ELISA method. Body composition was measured using two methods: bioimpedance analysis (BIA) and dual-energy X-ray absorptiometry (DXA).

RESULTS

There was a statistically significant difference (p =.038) in serum LL-37 level between patients with depression (3.55 ± 6.57 ng/mL) and control subjects (2.01 ± 3.88 ng/mL). Apart from visceral adipose tissue mass (%) in the depression group, we found no associations between serum LL-37 and analyzed anthropometric or body composition parameters.

CONCLUSIONS

Results of this study indicate that with the exception of visceral adipose tissue, LL-37 serum levels are not affected by anthropometric or body composition parameters. The association between visceral adipose tissue and LL-37 may indicate that visceral fat could be responsible for the increased LL-37 production.

Significance and Diagnostic Role of Antimicrobial Cathelicidins (LL-37) Peptides in Oral Health

Cathelicidins are a group of oral antimicrobial peptides that play multiple vital roles in the human body, such as their antimicrobial (broad spectrum) role against oral microbes, wound healing, and angiogenesis, with recent evidences about their role in cancer regulation. Cathelicidins are present in humans and other mammals as well. By complex interactions with the microenvironment, it results in pro-inflammatory effects. Many in vitro and in vivo experiments have been conducted to ultimately conclude that these unique peptides play an essential role in innate immunity. Peptides are released in the precursor form (defensins), which after cleavage results in cathelicidins formation. Living in the era where the major focus is on non-invasive and nanotechnology, this ultimately leads to further advancements in the field of salivaomics. Based on current spotlight innovations, we have highlighted the biochemistry, mode of action, and the importance of cathelicidins in the oral cavity.

Heightened circulating levels of antimicrobial peptides in tuberculosis-Diabetes co-morbidity and reversal upon treatment

BACKGROUND

The association of antimicrobial peptides (AMPs) with tuberculosis-diabetes comorbidity (PTB-DM) is not well understood.

METHODS

To study the association of AMPs with PTB-DM, we examined the systemic levels of cathelicidin (LL37), human beta defensin- 2 (HBD2), human neutrophil peptides 1-3, (HNP1-3) and granulysin in individuals with either PTB-DM, PTB, latent TB (LTB) or no TB infection (NTB).

RESULTS

Circulating levels of cathelicidin and HBD2 were significantly higher and granulysin levels were significantly lower in PTB-DM compared to PTB, LTB or NTB, while the levels of HNP1-3 were significantly higher in PTB-DM compared to LTB or NTB individuals. Moreover, the levels of cathelicidin and/or HBD2 were significantly higher in PTB-DM or PTB individuals with bilateral and cavitary disease and also exhibited a significant positive relationship with bacterial burden. Cathelidin, HBD2 and HNP1-3 levels exhibited a positive relationship with HbA1c and/or fasting blood glucose levels. Finally, anti-tuberculosis therapy resulted in significantly diminished levels of cathelicidin, HBD2, granulysin and significantly enhanced levels of HNP1-3 and granulysin in PTB-DM and/or PTB individuals.

CONCLUSION

Therefore, our data demonstrate that PTB-DM is associated with markedly enhanced levels of AMPs and diminished levels of granulysin.

Serum levels of peptide cathelicidin LL-37 in elderly patients with depression

Cathelicidin LL-37 is a small cationic that plays an important role in antimicrobial defense, as it kills a broad spectrum of infectious agents by disrupting their membranes, including gram-positive and gram-negative bacteria, some viruses and fungi; and it neutralizes activity of bacterial endotoxins. Moreover, cathelicidin LL-37 exerts proinflammatory effect, while numerous reports indicate the role of inflammation in the development of depression. The purpose of this study was to evaluate the circulating levels of cathelicidin LL-37 in elderly depressed patients. Thirty-nine elderly (age ≥ 60 years) women with major depressive disorder and thirty-eight non-depressed elderly (age ≥ 60 years) women were included into the study. The mean serum cathelicidin LL-37 concentration in patients with depression and in healthy subjects were 2.40 ± 3.00ng/mL and 1.17 ± 3.04ng/mL, respectively, and the difference was statistically significant. No significant differences between mean serum CRP level and WBC count in MDD patients and control group were documented. There were no correlations between LL-37 level and age, BMI, GDS score, CRP level or WBC count. It can be assumed that elevated serum LL-37 levels in depressed patients may reflect inflammatory activation associated with depression.

Evaluation of nasal fluid β-defensin 2 levels in children with allergic rhinitis

AIM

Knowledge about the role of the innate immune system in the pathogenesis of allergic diseases has been expanding in recent years. Defensins are antimicrobial peptides that are components of the innate immune system. Defensins have strong efficacy against bacterial, viral, and fungal infections. Moreover, they have regulatory functions in many physiologic processes such as antitumoral immunity, chemotaxis, inflammation, and wound healing. In this study, we aimed to investigate β-defensin 2 levels in the nasal fluids of children with allergic rhinitis.

MATERIAL AND METHODS

Study and control groups consisted of 28 patients with newly diagnosed allergic rhinitis who were not taking any medication, and 23 healthy children. Skin prick tests were performed on patients with allergic rhinitis and disease severity was assessed using the total symptom score. Nasal fluid samples were obtained using a modified polyurethane sponge absorption method from patients and control subjects. Nasal fluid β-defensin 2 levels were determined using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

The median value of nasal fluid β-defensin 2 levels were 173.8 pg/mL (interquartile range; 54.8-205.9 pg/mL) in allergic rhinitis group and 241.6 pg/mL (163.5-315.2 pg/mL) in the control group. There was a statistically significant difference between the two groups (p=0.01). Moreover, nasal fluid β-defensin 2 levels showed a significant negative correlation with total symptom scores (rho= -0.78, p<0.001).

CONCLUSIONS

Children with allergic rhinitis have reduced nasal fluid β-defensin 2 levels compared with controls, and β-defensin 2 levels were negatively correlated with disease severity. A more definite understanding of the roles of defensins and other antimicrobial peptides in allergic inflammation can open up new horizons in the management and treatment of these common diseases.

CD163 levels, pro- and anti-inflammatory cytokine secretion of monocytes in children with pulmonary tuberculosis

OBJECTIVES

Childhood tuberculosis (TB) comprises an important part of the world's TB burden. Monocytes set up the early phase of infection because of innate immune responses. Understanding the changes in monocyte subsets during multisystem infectious diseases may be important for the development of novel diagnostic and therapeutic strategies. The aim of this study was to evaluate the monocyte phenotype together with the cytokine secretion profiles of children with pulmonary tuberculosis.

STUDY DESIGN

Thirteen patients with pulmonary TB were enrolled as study group, and 14 healthy subjects as control group. Surface expressions of CD16, CD14, CD62L, CD163, CCR2, and HLA-DR of monocytes were analyzed by flow cytometry. The presence of IFN-γ, TNF-α, IL-10, IL-12, IL-23, and soluble form of CD163 (sCD163) in the antigen- and LPS-stimulated whole blood culture supernatants were detected using ELISA and Luminex.

RESULTS

Higher percentages of CD14⁺⁺ CD16⁺ and CD14⁺ CD16⁺⁺ monocyte subsets, and CCR2, CD62L and CD163 expression on circulating monocytes in children with pulmonary tuberculosis were obtained. Diminished levels of ESAT-6/CFP-10-induced IL-10 and increased levels of TB-antigen and LPS-stimulated sCD163 were found in childhood with pulmonary TB.

CONCLUSIONS

High expression of CD14⁺⁺ CD16⁺ , CD14⁺ CD16⁺⁺ , CD14⁺ CCR2⁺ , and CD14⁺ CD62L⁺ cells in childhood TB, and monocyte-derived cytokines reflected both pro- and anti-inflammatory profiles. Higher sCD163 and CD14⁺ CD163⁺ monocytes might help physicians in the differential diagnosis of pulmonary TB in children. Pediatr Pulmonol. 2017;52:675-683. © 2016 Wiley Periodicals, Inc.

Impact of high-dose vitamin D3 on plasma free 25-hydroxyvitamin D concentrations and antimicrobial peptides in critically ill mechanically ventilated adults

OBJECTIVES

High-dose vitamin D₃ increases plasma total 25-hydroxyvitamin D [25(OH)D] in critically ill, ventilated patients; however, to our knowledge, the effect on plasma levels of free (nonprotein-bound) 25(OH)D has not been investigated in critical illness. Moreover, the relationship of free 25(OH)D and the regulation of endogenous antimicrobial peptides (AMPs) remains unknown. The aims of this study were to determine in critically ill adults with respiratory failure the effect of previous high-dose regimens of vitamin D₃ on free 25(OH)D concentrations, the relationship of free 25(OH)D with circulating cathelicidin (LL-37) and human beta-defensin-2 (hBD-2), and the associations between plasma levels of free 25(OH)D and these AMPs to alveolar macrophage phagocytosis function.

METHODS

In a double blind, randomized controlled trial, critically ill ventilator-dependent adults (N = 30) received enteral vitamin D₃ (250,000 or 500,000 IU total over 5 d) or placebo. Plasma was obtained serially for concentrations of free 25(OH)D, LL-37, hBD-2, and expression of peripheral blood mononuclear cell human cationic antimicrobial protein (hCAP18) mRNA. Total 25(OH)D and LL-37 concentrations and alveolar macrophage phagocytosis were determined in bronchoalveolar lavage fluid.

RESULTS

Plasma concentrations of free 25(OH)D over time were correlated with total 25(OH)D levels (r= 0.82; P < 0.001). The increase in free 25(OH)D was greater with the 500 000 IU vitamin D₃ dose than with the lower dose. The percent change in mRNA expression of hCAP18 was positively associated with percent change in free 25(OH)D at days 7 and 14 (ρ = 0.48; P = 0.04 and ρ = 0.59; P = 0.03, respectively). Additionally, plasma LL-37 levels correlated with the percentage of alveolar macrophages exhibiting phagocytosis (ρ = 0.51; P = 0.04).

CONCLUSIONS

The present study found a dose-related increase in plasma free-25(OH)D levels, which was associated with increasing circulating mRNA expression of hCAP18 over time. There were no correlations between changes in total and free 25(OH)D against plasma LL-37 and hBD-2 concentrations. Larger studies appear warranted to determine the impact of high-dose vitamin D₃ administration on endogenous AMPs.

The dual role of cathelicidins in systemic inflammation

Antimicrobial peptides are key components of the innate immune system. They act as broad-spectrum antimicrobial agents against Gram-positive and -negative bacteria, viruses, and fungi. More recently, antimicrobial peptides have been ascribed immunomodulatory functions, including roles in wound healing, induction of cytokines, and altering host gene expression. Cathelicidins are a class of antimicrobial peptide found in humans, mice, and rats, among others. Known as LL-37 in humans and cathelin-related antimicrobial peptide (CRAMP) in rodents, cathelicidins are produced by many different cells, including macrophages, neutrophils, and epithelial cells. The role of cathelicidins is somewhat confounding, as they exhibit both pro-and anti-inflammatory activity. A major obstacle in the study of cathelicidins is the inability of exogenous LL-37 or CRAMP to mimic the activity of their endogenous counterparts. Nevertheless, studies have shown that LL-37 is recognized by multiple receptors, and may stabilize or modulate Toll-like receptor signaling. In addition, cathelicidins play a role in apoptosis, inflammasome activation, and phagocytosis. However, many studies are revealing the dual effects of cathelicidins. For example, CRAMP appears to be protective in models of group A Streptococcus skin infection, pneumonia, and meningitis, but detrimental in cases of severe bacterial infection, such as septic shock. It is becoming increasingly clear that the activity of cathelicidins is modulated by complex interactions with the microenvironment, as well as the disease background. This article reviews what is currently known about the activity of cathelicidins in an attempt to understand their complex roles in systemic diseases.

The Importance of First Impressions: Early Events in Mycobacterium tuberculosis Infection Influence Outcome

Tuberculosis remains a major health threat in much of the world. New vaccines against Mycobacterium tuberculosis are essential for preventing infection, disease, and transmission. However, the host immune responses that need to be induced by an effective vaccine remain unclear. Increasingly, it has become clear that early events in infection are of major importance in the eventual outcome of the infection. Studying such events in humans is challenging, as they occur within the lung and thoracic lymph nodes, and any clinical signs of early infection are relatively nonspecific. Nonetheless, clinical studies and animal models of tuberculosis have provided new insights into the local events that occur in the first few weeks of tuberculosis. Development of an effective vaccine requires a clear understanding of the successful (and detrimental) early host responses against M. tuberculosis, with the goal to improve upon natural immune responses and prevent infection or disease.