Importance of Endosomal Cathelicidin Degradation To Enhance DNA-Induced Chicken Macrophage Activation

Venom: A Promising Avenue for Antimicrobial Therapeutics

Venom in medicine is well documented in the chronicles of ancient Greece and the Roman Empire and persisted into the Renaissance and even into the modern era. Venoms were not always associated with detrimental consequences. Since ancient times, the curative capacity of venom has been recognized, portraying venom as a metaphor for pharmacy and medicine. Venom proteins and peptides' antimicrobial potential has not undergone systematic exploration despite the huge literature on natural antimicrobials. In light of the escalating challenge of antimicrobial resistance and the diminishing effectiveness of antibiotics, there is a pressing need for innovative antimicrobials capable of effectively addressing illnesses caused by multidrug-resistant microorganisms. This review adds to our understanding of the effectiveness of different venom components against a host of pathogenic microorganisms. The aim is to illuminate the various antimicrobials present in venom and venom peptides, thereby emphasizing the unexplored medicinal potential for antimicrobial properties. We have presented a concise summary of the molecular examination of the venom peptides' functioning processes, as well as the current clinical and preclinical progress of venom antimicrobial peptides.

Antibacterial activity of the antimicrobial peptide PMAP-36 in combination with tetracycline against porcine extraintestinal pathogenic Escherichia coli in vitro and in vivo

The increase in the emergence of antimicrobial resistance has led to great challenges in controlling porcine extraintestinal pathogenic Escherichia coli (ExPEC) infections. Combinations of antimicrobial peptides (AMPs) and antibiotics can synergistically improve antimicrobial efficacy and reduce bacterial resistance. In this study, we investigated the antibacterial activity of porcine myeloid antimicrobial peptide 36 (PMAP-36) in combination with tetracycline against porcine ExPEC PCN033 both in vitro and in vivo. The minimum bactericidal concentrations (MBCs) of AMPs (PMAP-36 and PR-39) against the ExPEC strains PCN033 and RS218 were 10 μM and 5 μM, respectively. Results of the checkerboard assay and the time-kill assay showed that PMAP-36 and antibiotics (tetracycline and gentamicin) had synergistic bactericidal effects against PCN033. PMAP-36 and tetracycline in combination led to PCN033 cell wall shrinkage, as was shown by scanning electron microscopy. Furthermore, PMAP-36 delayed the emergence of PCN033 resistance to tetracycline by inhibiting the expression of the tetracycline resistance gene tetB. In a mouse model of systemic infection of PCN033, treatment with PMAP-36 combined with tetracycline significantly increased the survival rate, reduced the bacterial load and dampened the inflammatory response in mice. In addition, detection of immune cells in the peritoneal lavage fluid using flow cytometry revealed that the combination of PMAP-36 and tetracycline promoted the migration of monocytes/macrophages to the infection site. Our results suggest that AMPs in combination with antibiotics may provide more therapeutic options against multidrug-resistant porcine ExPEC.

The immune enhancing effect of antimicrobial peptide LLv on broilers chickens

To evaluate the effect and its mechanism of heat-resistant antimicrobial peptide LLv on broilers, three hundred 1-day-old healthy AA+ female broilers were allocated into 5 groups with 6 replicates in each group and 10 birds in each replicate. Birds were given a basal diet, an antibiotic diet (10.2 mg/kg chlortetracycline hydrochloride), and the basal diet supplemented with 10, 50, and 100 mg/kg LLv for 42 d, respectively. Compared with the group which birds were fed an antibiotic-free basal diet (control group), supplementing 100 mg/kg LLv increased 21-day IgA, IgM, IL-4, AIV-Ab, IFN-γ levels and 42-day IgA, IgM, IL-4, AIV-Ab levels and reduced 42-day IL-1 levels in serum (P < 0.05). Compared with antibiotic group, the 10 and 50 mg/kg LLv decreased 42-day IgM levels in serum (P < 0.05). The 100 mg/kg LLv increased 21-day AIV-Ab levels and 42-day IL-4, AIV-Ab levels and reduced 42-day IL-1 levels in serum (P < 0.05). Compared with control group, the 100 mg/kg LLv increased the expression rate of sIgA secretory cells and sIgA content in jejunal mucosa at 21 d and 42 d (P < 0.05), which did not differ from antibiotic group (P > 0.05). Compared with antibiotic group, the 10 mg/kg LLv reduced 21-day sIgA content and the 50 mg/kg LLv reduced 42-d the expression rate of sIgA secretory cells in jejunal mucosa (P < 0.05). Compared with control group, the 100 mg/kg LLv increased the expression of TCR, IL-15, CD28, BAFF, CD86, CD83, MHC-II, and CD40 genes in jejunal mucosa at 21 d and 42 d (P < 0.05). Compared with antibiotic group, the 100 mg/kg LLv increased the expression of 21-day BAFF, CD40, MHC-II, CD83 genes and the expression of 42-day BAFF, TCR, IL-15, CD40, CD83 genes in jejunal mucosa (P < 0.05). The results showed that the addition of LLv to the ration had a promotional effect on the immune function of broiler chickens.

Identification and Characterization of a Novel Cathelicidin from Hydrophis cyanocinctus with Antimicrobial and Anti-Inflammatory Activity

The abuse of antibiotics and lack of new antibacterial drugs has led to the emergence of superbugs that raise fears of untreatable infections. The Cathelicidin family of antimicrobial peptide (AMP) with varying antibacterial activities and safety is considered to be a promising alternative to conventional antibiotics. In this study, we investigated a novel Cathelicidin peptide named Hydrostatin-AMP2 from the sea snake Hydrophis cyanocinctus. The peptide was identified based on gene functional annotation of the H. cyanocinctus genome and bioinformatic prediction. Hydrostatin-AMP2 showed excellent antimicrobial activity against both Gram-positive and Gram-negative bacteria, including standard and clinical Ampicillin-resistant strains. The results of the bacterial killing kinetic assay demonstrated that Hydrostatin-AMP2 had faster antimicrobial action than Ampicillin. Meanwhile, Hydrostatin-AMP2 exhibited significant anti-biofilm activity including inhibition and eradication. It also showed a low propensity to induce resistance as well as low cytotoxicity and hemolytic activity. Notably, Hydrostatin-AMP2 apparently decreased the production of pro-inflammatory cytokines in the LPS-induced RAW264.7 cell model. To sum up, these findings indicate that Hydrostatin-AMP2 is a potential peptide candidate for the development of new-generation antimicrobial drugs fighting against antibiotic-resistant bacterial infections.

Human Cytomegalovirus Induces Vitamin-D Resistance In Vitro by Dysregulating the Transcriptional Repressor Snail

Vitamin-D supplementation is considered to play a beneficial role against multiple viruses due to its immune-regulating and direct antimicrobial effects. In contrast, the human cytomegalovirus (HCMV) has shown to be resistant to treatment with vitamin D in vitro by downregulation of the vitamin-D receptor. In this study, we aimed to elucidate the mechanism and possible biological consequences of vitamin-D resistance during HCMV infection. Mechanistically, HCMV induced vitamin-D resistance by downregulating the vitamin-D receptor (VDR) within hours of lytic infection. We found that the VDR was inhibited at the promoter level, and treatment with histone deacetylase inhibitors could restore VDR expression. VDR downregulation highly correlated with the upregulation of the transcriptional repressor Snail1, a mechanism likely contributing to the epigenetic inactivation of the VDR promoter, since siRNA-mediated knockdown of Snail partly restored levels of VDR expression. Finally, we found that direct addition of the vitamin-D-inducible antimicrobial peptide LL-37 strongly and significantly reduced viral titers in infected fibroblasts, highlighting VDR biological relevance and the potential of vitamin-D-inducible peptides for the antiviral treatment of vitamin-D deficient patients.

Chicken cathelicidin-2 promotes NLRP3 inflammasome activation in macrophages

Chicken cathelicidin-2 (CATH-2) as a host defense peptide has been identified to have potent antimicrobial and immunomodulatory activities. Here, we reported the mechanism by which CATH-2 modulates NLRP3 inflammasome activation. Our results show that CATH-2 and ATP as a positive control induced secretion of IL-1β and IL-1α in LPS-primed macrophages but did not affect secretion of IL-6, IL-12 and TNF-α. Furthermore, CATH-2 induced caspase-1 activation and oligomerization of apoptosis-associated speck-like protein containing a carboxy- terminal caspase recruitment domain (ASC), which is essential for NLRP3 inflammasome activation. However, CATH-2 failed to induce IL-1β secretion in Nlrp3^-/-, Asc^-/- and Casp1^-/- macrophages. Notably, IL-1β and NLRP3 mRNA expression were not affected by CATH-2. In addition, CATH-2-induced NLRP3 inflammasome activation was mediated by K⁺ efflux but independent of the P2X7 receptor that is required for ATP-mediated K⁺ efflux. Gene interference of NEK7 kinase which has been identified to directly interact with NLRP3, significantly reduced IL-1β secretion and caspase-1 activation induced by CATH-2. Furthermore, confocal microscopy shows that CATH-2 significantly induced lysosomal leakage with the diffusion of dextran fluorescent signal. Cathepsin B inhibitors completely abrogated IL-1β secretion and caspase-1 activation as well as attenuating the formation of ASC specks induced by CATH-2. These results all indicate that CATH-2-induced activation of NLRP3 inflammasome is mediated by K⁺ efflux, and involves the NEK7 protein and cathepsin B. In conclusion, our study shows that CATH-2 acts as a second signal to activate NLRP3 inflammasome. Our study provides new insight into CATH-2 modulating immune response.

Novel insights in antimicrobial and immunomodulatory mechanisms of action of PepBiotics CR-163 and CR-172

OBJECTIVES

Recently our group developed a novel group of antimicrobial peptides termed PepBiotics, of which peptides CR-163 and CR-172 showed optimized antibacterial activity against Pseudomonas aeruginosa and Staphylococcus aureus without inducing antimicrobial resistance. In this study, the antibacterial mechanism of action and the immunomodulatory activity of these two PepBiotics was explored.

METHODS

RAW264.7 cells were used to determine the ability of PepBiotics to neutralize LPS-and LTA-induced activation of macrophages. Isothermal titration calorimetry and competition assays with dansyl-labeled polymyxin B determined binding characteristics to LPS and LTA. Combined bacterial killing with subsequent macrophage activation assays was performed to determine so-called silent killing'. Finally, flow cytometry of peptide-treated genetically engineered E. coli,expressing GFP and mCherry in the cytoplasm and periplasm, respectively further established the antimicrobial mechanism of PepBiotics.

RESULTS

Both CR-163 and CR-172 were shown to have broad-spectrum activity against ESKAPE pathogens and E. coli, using a membranolytic mechanism of action. PepBiotics could exothermically bind LPS/LTA and were able to replace polymyxin B. Finally, it was demonstrated that bacteria killed by PepBiotics were less prone to stimulate immune cells, contrary to gentamicin and heat-killed bacteria that still elicited a strong immune response CONCLUSIONS: These studies highlight the multifunctional nature of the two peptide antibiotics as both broad spectrum antimicrobial and immunomodulator. Their ability to kill bacteria and reduce unwanted subsequent immune activation is a major advantage and highlights their potential for future therapeutic use.

ACUTE AND SUSTAINED ALTERATIONS TO THE BONE MARROW IMMUNE MICROENVIRONMENT FOLLOWING POLYMICROBIAL INFECTION

ABSTRACT

Sepsis is a highly prevalent cause of death in intensive care units. Characterized by severe immune cell derangements, sepsis is often associated with multiorgan dysfunction. For many sepsis survivors, these deficits can persist long after clinical resolution of the underlying infection. Although many studies report on the impact of sepsis on individual immune cell subtypes, a comprehensive analysis of sepsis-induced alterations within and across the immune cell landscape is lacking. In this study, we used single-cell RNA sequencing to assess sepsis-associated transcriptional changes in immune cells isolated from bone marrow at single-cell resolution. We used a high-survival fecal-induced peritonitis sepsis model using Friend leukemia virus B mice. Single-cell RNA sequencing classified 3402 single cells from control subjects into 14 clusters representing long-term hematopoietic stem cell (HSC), short-term HSC, basophil, dendritic cell, eosinophil, erythroblast, erythrocyte, macrophage, neutrophil, natural killer cell, plasma cell, plasmacytoid dendritic cell, pre-B cell, and T memory cell lineages. One day following experimentally induced sepsis, cell type compositions shifted significantly and included notable decreases in HSC and myeloid cell abundance. In addition to proportional cell composition changes, acute sepsis induced significant transcriptional alterations in most immune cell types analyzed-changes that failed to completely resolve 1 month after sepsis. Taken together, we report widespread and persistent transcriptional changes in diverse immune cells in response to polymicrobial infection. This study will serve as a valuable resource for future work investigating acute and/or long-term sepsis-associated immune cell derangements.

Chicken cathelicidin-2 promotes IL-1β secretion via the NLRP3 inflammasome pathway and serine proteases activity in LPS-primed murine neutrophils

Cathelicidins have antimicrobial and immunomodulatory activities. Previous studies have shown that chicken cathelicidin-2 (CATH-2) exerts strong anti-inflammatory activity through LPS neutralization. However, it is still unclear whether other intracellular signaling pathways are involved in CATH-2 immunomodulation. Therefore, the CATH-2-meadiated immune response was investigated in LPS-primed neutrophils. Firstly, inflammatory cytokines release was determined in LPS-primed neutrophils. The results showed that CATH-2 significantly promoted secretion of IL-1β and IL-1α while IL-6 and TNF-α were not affected. IL-1β is the key indicator of inflammasome activation. Next, NLRP3 inflammasome signaling pathway was explored using neutrophils of Nlrp3^-/-, Asc^-/- and Casp1^-/- mice and the results showed that the CATH-2-enhanced IL-1β release was completely abrogated, indicating it is NLRP3-dependent. Moreover, CATH-2 significantly induced activation of caspase-1 and gasdermin D (GSDMD) but did not affect LPS-induced mRNA expression of IL-1β and NLRP3, demonstrating that CATH-2 serves as the second signal activating the NLRP3 inflammasome. Furthermore, CATH-2-mediated IL-1β secretion and caspase-1 activation is dependent on potassium efflux but independent of P2X7R. In addition, other signaling pathways including JNK, ERK and SyK were investigated using different inhibitors and the results showed that these signaling pathway inhibitors partially attenuated CATH-2-enhanced IL-1β secretion, especially the JNK inhibitor. Finally, the role of serine protease in CATH-2-mediated NLRP3 inflammasome activation was investigated in neutrophils and the results showed that serine protease activity is involved in CATH-2-enhanced IL-1β secretion and caspase-1 activation. In conclusion, after LPS priming in neutrophils, CATH-2 can be an agonist of the NLRP3 inflammasome. Our study increases the understanding on immunomodulatory effects of chicken cathelicidins and provides new insight on chicken cathelicidins-mediated immune response.

Anticancer activity of chicken cathelicidin peptides against different types of cancer

BACKGROUND

This study served as the pioneer in studying the anti-cancer role of chicken cathelicidin peptides.

METHODS AND RESULTS

Chicken cathelicidins were used as anticancer agent against the breast cancer cell line (MCF-7) and human colon cancer cell line (HCT116). In addition, the mechanism of action of the interaction of cationic peptides with breast cancer cell line MCF-7 was also investigated. An in vivo investigation was also achieved to evaluate the role of chicken cathelicidin in Ehrlich ascites cell (EAC) suppression as a tumor model after subcutaneous implantation in mice. It was found during the study that exposure of cell lines to 40 µg/ml of chicken cathelicidin for 72 h reduced cell lines growth rate by 90-95%. These peptides demonstrated down-regulation of (cyclin A1 and cyclin D genes) of MCF-7 cells. The study showed that two- and three-fold expression of both of caspase-3 and - 7 genes in untreated MCF-7 cells compared to treated MCF-7 cells with chicken cathelicidin peptides. Our data showed that chicken (CATH-1) enhance releasing of TNFα, INF-γ and upregulation of granzyme K in treated mice groups, in parallel, the tumor size and volume was reduced in the treated EAC-bearing groups. Tumor of mice groups treated with chicken cathelicidin displayed high area of necrosis compared to untreated EAC-bearing mice. Based on histological analysis and immunohistochemical staining revealed that the tumor section in Ehrlich solid tumor exhibited a strong Bcl2 expression in untreated control compared to mice treated with 10 & 20 µg of cathelicidin. Interestingly, low expression of Bcl2 were observed in mice taken 40 µg/mL of CATH-1.

CONCLUSIONS

This study drive intention in treatment of cancer through the efficacy of anticancer efficacy of chicken cathelicidin peptides.

d-enantiomers of CATH-2 enhance the response of macrophages against Streptococcus suis serotype 2

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D-CATH-2 has strong antimicrobial activities towards multiple S.suis strains.

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D-CATH-2 ameliorates macrophage function.

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DCATH-2 binds LTA.

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DCATH-2 has prophylactic effect against S. suis infection in vivo.

Introduction

Due to the increase of antibiotic resistant bacterial strains, there is an urgent need for development of alternatives to antibiotics. Cathelicidins can be such an alternative to antibiotics having both a direct antimicrobial capacity as well as an immunomodulatory function. Previously, the full d-enantiomer of chicken cathelicidin-2 (d-CATH-2) has shown to prophylactically protect chickens against infection 7 days post hatch when administered in ovo three days before hatch.

Objectives

To further evaluate d-CATH-2 in mammals as a candidate for an alternative to antibiotics.

In this study, the prophylactic capacity of d-CATH-2 and two truncated derivatives, d-C(1–21) and d-C(4–21), was determined in mammalian cells.

Methods

Antibacterial assays; immune cell differentiation and modulation; cytotoxicity, isothermal titration calorimetry; in vivo prophylactic capacity of peptides in an S. suis infection model.

Results

d-CATH-2 and its derivatives were shown to have a strong direct antibacterial capacity against four different S. suis serotype 2 strains (P1/7, S735, D282, and OV625) in bacterial medium and even stronger in cell culture medium. In addition, d-CATH-2 and its derivatives ameliorated the efficiency of mouse bone marrow-derived macrophages (BMDM) and skewed mouse bone marrow-derived dendritic cells (BMDC) towards cells with a more macrophage-like phenotype. The peptides directly bind lipoteichoic acid (LTA) and inhibit LTA-induced activation of macrophages. In addition, S. suis killed by the peptide was unable to further activate mouse macrophages, which indicates that S. suis was eliminated by the previously reported silent killing mechanism. Administration of d-C(1–21) at 24 h or 7 days before infection resulted in a small prophylactic protection with reduced disease severity and reduced mortality of the treated mice.

Conclusion

d-enantiomers of CATH-2 show promise as anti-infectives against pathogenic S. suis for application in mammals.

The cathelicidin CATH-2 efficiently neutralizes LPS- and E. coli-induced activation of porcine bone marrow derived macrophages

Infectious diseases in pigs cause monetary loss to farmers and pose a zoonotic risk. Therefore, it is important to obtain more porcine specific immunological knowledge as a measure to protect against infectious diseases, for example by exploring immunomodulators that are usable as vaccine adjuvants. Cathelicidins are a class of host defence peptides (HDPs) able to directly kill microbes as well as exert a diverse range of effects on the immune system. The peptides have shown promise as immunomodulatory peptides in many applications, including vaccines. However, it is currently unknown what the precise effect of these peptides is on porcine immune cells and whether peptides of other species might also have a strong immunomodulatory effect on porcine macrophages. Mononuclear bone marrow cells of pigs, aged 5-6 months, were cultured into M1 or M2 macrophages and stimulated with LPS or whole bacteria in the presence of host defence peptides (HDPs). CATH-2 and LL-37 strongly inhibited LPS-induced activation of M1 macrophages, the inhibition of LPS-induced activation of M2 macrophages by HDPs was milder, showing that the peptides have selective effects on different cell types. Upon stimulation with whole bacteria, only CATH-2 could effectively inhibit macrophage activation, showing the potent anti-inflammatory potential of this peptide. These results show that porcine peptides are not necessarily the most active in a porcine system, and that CATH-2 is effective in a porcine system as an anti-inflammatory immune modulator, which can be used, for example, in inactivated pathogen vaccines.

The bird's immune response to avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) cause colibacillosis in birds, a syndrome of severe respiratory and systemic disease that constitutes a major threat due to early mortality, condemnation of carcasses and reduced productivity. APEC can infect different types of birds in all commercial settings, and birds of all ages, although disease tends to be more severe in younger birds likely a consequence of an immature immune system. APEC can act as both primary and secondary pathogens, with predisposing factors for secondary infections including poor housing conditions, respiratory viral and Mycoplasma spp. infections or vaccinations. Controlled studies with APEC as primary pathogens have been used to study the bird's immune response to APEC, although it may not always be representative of natural infections which may be more complex due to the presence of secondary agents, stress and environmental factors. Under controlled experimental conditions, a strong early innate immune response is induced which includes host defence peptides in mucus and a cellular response driven by heterophils and macrophages. Both antibody and T-cell mediated adaptive responses have been demonstrated after vaccination. In this review we will discuss the bird's immune response to APEC as primary pathogen with a bias towards the innate immune response, as mechanistic adaptive studies clearly form a much more limited body of work despite numerous vaccine trials.

Mechanistic Insights into the Leishmanicidal and Bactericidal Activities of Batroxicidin, a Cathelicidin-Related Peptide from a South American Viper (Bothrops atrox)

Snake venoms are important sources of bioactive molecules, including those with antiparasitic activity. Cathelicidins form a class of such molecules, which are produced by a variety of organisms. Batroxicidin (BatxC) is a cathelicidin found in the venom of the common lancehead (Bothrops atrox). In the present work, BatxC and two synthetic analogues, BatxC(C-2.15Phe) and BatxC(C-2.14Phe)des-Phe1, were assessed for their microbicidal activity. All three peptides showed a broad-spectrum activity on Gram-positive and -negative bacteria, as well as promastigote and amastigote forms of Leishmania (Leishmania) amazonensis. Circular dichroism (CD) and nuclear magnetic resonance (NMR) data indicated that the three peptides changed their structure upon interaction with membranes. Biomimetic membrane model studies demonstrated that the peptides exert a permeabilization effect in prokaryotic membranes, leading to cell morphology distortion, which was confirmed by atomic force microscopy (AFM). The molecules considered in this work exhibited bactericidal and leishmanicidal activity at low concentrations, with the AFM data suggesting membrane pore formation as their mechanism of action. These peptides stand as valuable prototype drugs to be further investigated and eventually used to treat bacterial and protozoal infections.

The immunomodulatory effect of cathelicidin-B1 on chicken macrophages

Cathelicidins (CATHs) play an important role in the innate immune response against microbial infections. Among the four chicken cathelicidins, CATH-B1 is studied the least. In this study, the effect of CATH-B1 on the macrophage response towards avian pathogenic E. coli (APEC) and bacterial ligands was investigated. Our results show that APEC induced CATH-B1 gene expression in both a chicken macrophage cell line (HD11 cells) and primary macrophages, while expression of the other three CATHs was virtually unaffected. While the antimicrobial activity of CATH-B1 is very low under cell culture conditions, it enhanced bacterial phagocytosis by macrophages. Interestingly, CATH-B1 downregulated APEC-induced gene expression of pro-inflammatory cytokines (IFN-β, IL-1β, IL-6 and IL-8) in primary macrophages. In addition, CATH-B1 pre-incubated macrophages showed a significantly higher gene expression of IL-10 after APEC challenge, indicating an overall anti-inflammatory profile for CATH-B1. Using isothermal titration calorimetry (ITC), CATH-B1 was shown to bind LPS. This suggests that CATH-B1 reduces toll like receptor (TLR) 4 dependent activation by APEC which may partly explain the decreased production of pro-inflammatory cytokines by macrophages. On the contrary, direct binding of CATH-B1 to ODN-2006 enhanced the TLR21 dependent activation of macrophages as measured by nitric oxide production. In conclusion, our results show for the first time that CATH-B1 has several immunomodulatory activities and thereby could be an important factor in the chicken immune response.

Cathelicidins Modulate TLR-Activation and Inflammation

Cathelicidins are short cationic peptides that are part of the innate immune system. At first, these peptides were studied mostly for their direct antimicrobial killing capacity, but nowadays they are more and more appreciated for their immunomodulatory functions. In this review, we will provide a comprehensive overview of the various effects cathelicidins have on the detection of damage- and microbe-associated molecular patterns, with a special focus on their effects on Toll-like receptor (TLR) activation. We review the available literature based on TLR ligand types, which can roughly be divided into lipidic ligands, such as LPS and lipoproteins, and nucleic-acid ligands, such as RNA and DNA. For both ligand types, we describe how direct cathelicidin-ligand interactions influence TLR activation, by for instance altering ligand stability, cellular uptake and receptor interaction. In addition, we will review the more indirect mechanisms by which cathelicidins affect downstream TLR-signaling. To place all this information in a broader context, we discuss how these cathelicidin-mediated effects can have an impact on how the host responds to infectious organisms as well as how these effects play a role in the exacerbation of inflammation in auto-immune diseases. Finally, we discuss how these immunomodulatory activities can be exploited in vaccine development and cancer therapies.

Characterization of splenic MRC1hiMHCIIlo and MRC1loMHCIIhi cells from the monocyte/macrophage lineage of White Leghorn chickens

Monocytes/macrophages, which are found in a variety of organs, maintain tissue homeostasis at a steady state and act as the first line of defence during pathogen-induced inflammation in the host. Most monocyte/macrophage lineage studies in chickens have been largely performed using cell lines, while few studies using primary cells have been conducted. In the present study, the phenotypic and functional characteristics of splenic monocyte/macrophage lineage cells during steady state and inflammatory conditions were examined. Splenic monocyte/macrophage lineage cells could be identified as MRC1^loMHCII^hi and MRC1^hiMHCII^lo cells based on their surface expression of MRC1 and MHCII. In the steady state, MRC1^loMHCII^hi cells were more frequently found among MRC1⁺ cells. MRC1^loMHCII^hi cells expressed a higher number of antigen-presenting molecules (MHCII, MHCI, and CD80) than MRC1^hiMHCII^lo cells. In contrast, MRC1^hiMHCII^lo cells showed better phagocytic and CCR5-dependent migratory properties than MRC1^loMHCII^hi cells. Furthermore, MRC1^hiMHCII^lo cells infiltrated the spleen in vivo and then became MRC1^loMHCII^hi cells. During lipopolysaccharide (LPS)-induced inflammatory conditions that were produced via intraperitoneal (i.p.) injection, the proportion and absolute number of MRC1^hiMHCII^lo cells were increased in the spleen. Uniquely, inflammation induced the downregulation of MHCII expression in MRC1^hiMHCII^lo cells. The major source of inflammatory cytokines (IL-1β, IL-6, and IL-12) was MRC1^loMHCII^hi cells. Furthermore, MRC1^hiMHCII^lo cells showed greater bactericidal activity than MRC1^loMHCII^hi cells during LPS-induced inflammation. Collectively, these results suggest that two subsets of monocyte/macrophage lineage cells exist in the chicken spleen that have functional differences.

Antiviral Activity of Chicken Cathelicidin B1 Against Influenza A Virus

Cathelicidins (CATHs) are host defense peptides (HDPs) that play an important role in the innate immune response against infections. Although multiple functions of cathelicidins have been described, including direct antimicrobial activity and several immunomodulatory effects on the host, relatively little is known about their antiviral activity. Therefore, in vitro antiviral activity of chicken cathelicidins and the underlying mechanism was investigated in this study against different influenza A virus (IAV) strains. Our results show that chicken CATH-B1 has broad anti-IAV activity compared to other cathelicidins (CATH-1, -2, -3, LL-37, PMAP-23, and K9CATH) with an inhibition of viral infection up to 80% against three tested IAV strains (H1N1, H3N1, and H5N1). In agreement herewith, CATH-B1 affected virus-induced inflammatory cytokines expression (IFN-β, IL-1β, IL-6, and IL-8). Incubation of cells with CATH-B1 prior to or after their inoculation with virus did not reduce viral infection indicating that direct interaction of virus with the peptide was required for CATH-B1’s antiviral activity. Experiments using combined size exclusion and affinity-based separation of virus and peptide also indicated that CATH-B1 bound to viral particles. In addition, using electron microscopy, no morphological change of the virus itself was seen upon incubation with CATH-B1 but large aggregates of CATH-B1 and viral particles were observed, indicating that aggregation might be the mechanism of action reducing IAV infectivity. Neuraminidase (NA) activity assays using monovalent or multivalent substrates, indicated that CATH-B1 did not affect NA activity per se, but negatively affected the ability of virus particles to interact with multivalent receptors, presumably by interfering with hemagglutinin activity. In conclusion, our results show CATH-B1 has good antiviral activity against IAV by binding to the viral particle and thereby blocking viral entry.

Chicken CATH-2 Increases Antigen Presentation Markers on Chicken Monocytes and Macrophages

Abstract: Background

Cathelicidins are a family of Host Defense Peptides (HDPs), that play an important role in the innate immune response. They exert both broad-spectrum antimicrobial activity against pathogens, and strong immunomodulatory functions that affect the response of innate and adaptive immune cells.

Objective

The aim of this study was to investigate immunomodulation by the chicken cathelicidin CATH-2 and compare its activities to those of the human cathelicidin LL-37.

Methods

Chicken macrophages and chicken monocytes were incubated with cathelicidins. Activation of immune cells was determined by measuring surface markers Mannose Receptor C-type 1 (MRC1) and MHC-II. Cytokine production was measured by qPCR and nitric oxide production was determined using the Griess assay. Finally, the effect of cathelicidins on phagocytosis was measured using carboxylate-modified polystyrene latex beads.

Results

CATH-2 and its all-D enantiomer D-CATH-2 increased MRC1 and MHC-II expression, markers for antigen presentation, on primary chicken monocytes, whereas LL-37 did not. D-CATH-2 also increased the MRC1 and MHC-II expression if a chicken macrophage cell line (HD11 cells) was used. In addition, LPS-induced NO production by HD11 cells was inhibited by CATH-2 and D-CATH-2.

Conclusion

These results are a clear indication that CATH-2 (and D-CATH-2) affect the activation state of monocytes and macrophages, which leads to optimization of the innate immune response and enhancement of the adaptive immune response.

The Control of Intestinal Inflammation: A Major Objective in the Research of Probiotic Strains as Alternatives to Antibiotic Growth Promoters in Poultry

The reduction of antimicrobial resistance is a major challenge for the scientific community. In a few decades, infections by resistant bacteria are forecasted to be the main cause of death in the world. The withdrawal of antibiotics as growth promoters and their preventive use in animal production is essential to avoid these resistances, but this may impair productivity and health due to the increase in gut inflammation. This reduction in productivity aggravates the problem of increasing meat demand in developing countries and limits the availability of raw materials. Probiotics are promising products to address this challenge due to their beneficial effects on microbiota composition, mucosal barrier integrity, and immune system to control inflammation. Although many modes of action have been demonstrated, the scientific community is not able to describe the specific effects that a probiotic should induce on the host to maximize both productivity and animal health. First, it may be necessary to define what are the innate immune pathways acting in the gut that optimize productivity and health and to then investigate which probiotic strain is able to induce the specific effect needed. This review describes several gaps in the knowledge of host-microbiota-pathogen interaction and the related mechanisms involved in the inflammatory response not demonstrated yet in poultry.

Snake Venom Cathelicidins as Natural Antimicrobial Peptides

Bioactive small molecules isolated from animals, plants, fungi and bacteria, including natural antimicrobial peptides, have shown great therapeutic potential worldwide. Among these peptides, snake venom cathelicidins are being widely exploited, because the variation in the composition of the venom reflects a range of biological activities that may be of biotechnological interest. Cathelicidins are short, cationic, and amphipathic molecules. They play an important role in host defense against microbial infections. We are currently facing a strong limitation on pharmacological interventions for infection control, which has become increasingly complex due to the lack of effective therapeutic options. In this review, we will focus on natural snake venom cathelicidins as promising candidates for the development of new antibacterial agents to fight antibiotic-resistant bacteria. We will highlight their antibacterial and antibiofilm activities, mechanism of action, and modulation of the innate immune response.

Cathelicidins PMAP-36, LL-37 and CATH-2 are similar peptides with different modes of action

Host defense peptides (HDPs) play a pivotal role in innate immunity and have, in addition to antimicrobial activity, also important immunomodulatory functions. Bacteria are less likely to develop resistance against HDPs because these peptides target and kill bacteria in multiple ways, as well as modulate the immune system. Therefore, HDPs, and derivatives thereof, are promising alternatives to traditional antibiotics. Hardly anything is known about the immunomodulatory functions of porcine cathelicidin PMAP-36. In this study, we aimed to determine both antibacterial and immunomodulatory activities of PMAP-36 comparing the properties of PMAP-36 analogs with two well-studied peptides, human LL-37 and chicken CATH-2. Transmission electron microscopy revealed different killing mechanisms of E. coli for PMAP-36, CATH-2 and LL-37. LL-37 binds LPS very weakly in contrast to PMAP-36, but it inhibits LPS activation of macrophages the strongest. The first 11 amino acids of the N-terminal side of PMAP-36 are dispensable for E. coli killing, LPS-neutralization and binding. Deletion of four additional amino acids resulted in a strong decrease in activity. The activity of full length PMAP-36 was not affected by monomerization, whereas the shorter analogs require dimerization for proper immunomodulatory activity but not for their antibacterial activity.

Cathelicidins: Immunomodulatory Antimicrobials

Cathelicidins are host defense peptides with antimicrobial and immunomodulatory functions. These effector molecules of the innate immune system of many vertebrates are diverse in their amino acid sequence but share physicochemical characteristics like positive charge and amphipathicity. Besides being antimicrobial, cathelicidins have a wide variety in immunomodulatory functions, both boosting and inhibiting inflammation, directing chemotaxis, and effecting cell differentiation, primarily towards type 1 immune responses. In this review, we will examine the biology and various functions of cathelicidins, focusing on putting in vitro results in the context of in vivo situations. The pro-inflammatory and anti-inflammatory functions are highlighted, as well both direct and indirect effects on chemotaxis and cell differentiation. Additionally, we will discuss the potential and limitations of using cathelicidins as immunomodulatory or antimicrobial drugs.

The potential for immunoglobulins and host defense peptides (HDPs) to reduce the use of antibiotics in animal production

Innate defense mechanisms are aimed at quickly containing and removing infectious microorganisms and involve local stromal and immune cell activation, neutrophil recruitment and activation and the induction of host defense peptides (defensins and cathelicidins), acute phase proteins and complement activation. As an alternative to antibiotics, innate immune mechanisms are highly relevant as they offer rapid general ways to, at least partially, protect against infections and enable the build-up of a sufficient adaptive immune response. This review describes two classes of promising alternatives to antibiotics based on components of the innate host defense. First we describe immunoglobulins applied to mimic the way in which they work in the newborn as locally acting broadly active defense molecules enforcing innate immunity barriers. Secondly, the potential of host defense peptides with different modes of action, used directly, induced in situ or used as vaccine adjuvants is described.

Immunomodulation and effects on microbiota after in ovo administration of chicken cathelicidin-2

Host Defense Peptides (HDPs) such as cathelicidins are multifunctional effectors of the innate immune system with both antimicrobial and pleiotropic immunomodulatory functions. Chicken cathelicidin-2 (CATH-2) has multiple immunomodulatory effects in vitro and the D-amino acid analog of this peptide has been shown to partially protect young chicks from a bacterial infection. However, the mechanisms responsible for CATH-2 mediated in vivo protection have not been investigated so far. In this study, D-CATH-2 was administered in ovo and the immune status and microbiota of the chicks were investigated at 7 days posthatch to elucidate the in vivo mechanisms of the peptide. In three consecutive studies, no effects on numbers and functions of immune cells were found and only small changes were seen in gene expression of Peripheral Blood Mononuclear Cells (PBMCs). In two studies, intestinal microbiota composition was determined which was highly variable, suggesting that it was strongly influenced by environmental factors. In both studies, in ovo D-CATH-2 treatment caused significant reduction of Ruminococcaceae and Butyricicoccus in the cecum and Escherichia/Shigella in both ileum and cecum. In conclusion, this study shows that, in the absence of an infectious stimulus, in ovo administration of a CATH-2 analog alters the microbiota composition but does not affect the chicks' immune system posthatch.

Imaging the Antistaphylococcal Activity of CATH-2: Mechanism of Attack and Regulation of Inflammatory Response

Chicken cathelicidin-2 (CATH-2) is a broad-spectrum antimicrobial host defense peptide (HDP) that may serve as a paradigm for the development of new antimicrobial agents. While previous studies have elucidated the mechanism by which CATH-2 kills Escherichia coli, its mode of action against Gram-positive bacteria remains to be determined. In this study, we explored the underlying antibacterial mechanism of CATH-2 against a methicillin-resistant strain of Staphylococcus aureus and the effect of CATH-2-mediated S. aureus killing on immune activation. Visualization of the antimicrobial activity of CATH-2 against S. aureus with live-imaging confocal microscopy demonstrated that CATH-2 directly binds the bacteria, which is followed by membrane permeabilization and cell shrinkage. Transmission electron microscopy (TEM) studies further showed that CATH-2 initiated pronounced morphological changes of the membrane (mesosome formation) and ribosomal structures (clustering) in a dose-dependent manner. Immunolabeling of these sections demonstrated that CATH-2 binds and passes the bacterial membrane at subminimal bactericidal concentrations (sub-MBCs). Furthermore, competition assays and isothermal titration calorimetry (ITC) analysis provided evidence that CATH-2 directly interacts with lipoteichoic acid and cardiolipin. Finally, stimulation of macrophages with S. aureus and CATH-2 showed that CATH-2 not only kills S. aureus but also has the potential to limit S. aureus-induced inflammation at or above the MBC. Taken together, it is concluded that at sub-MBCs, CATH-2 perturbs the bacterial membrane and subsequently enters the cell and binds intracellular S. aureus components, while at or above the MBC, CATH-2 causes disruption of membrane integrity and inhibits S. aureus-induced macrophage activation. IMPORTANCE Due to the high use of antibiotics in both human and veterinary settings, many bacteria have become resistant to those antibiotics that we so heavily rely on. Methicillin-resistant S. aureus (MRSA) is one of these difficult-to-treat resistant pathogens for which novel antimicrobial therapies will be required in the near future. One novel approach could be the utilization of naturally occurring antimicrobial peptides, such as chicken CATH-2, which have been show to act against a wide variety of bacteria. However, before these peptides can be used clinically, more knowledge of their functions and mechanisms of action is required. In this study, we used live imaging and electron microscopy to visualize in detail how CATH-2 kills S. aureus, and we investigated how CATH-2 affects immune activation by S. aureus. Together, these results give a better understanding of how CATH-2 kills S. aureus and what the potential immunological consequences of this killing can be.

Cathelicidins Inhibit Escherichia coli-Induced TLR2 and TLR4 Activation in a Viability-Dependent Manner

Activation of the immune system needs to be tightly regulated to provide protection against infections and, at the same time, to prevent excessive inflammation to limit collateral damage to the host. This tight regulation includes regulating the activation of TLRs, which are key players in the recognition of invading microbes. A group of short cationic antimicrobial peptides, called cathelicidins, have previously been shown to modulate TLR activation by synthetic or purified TLR ligands and may play an important role in the regulation of inflammation during infections. However, little is known about how these cathelicidins affect TLR activation in the context of complete and viable bacteria. In this article, we show that chicken cathelicidin-2 kills Escherichia coli in an immunogenically silent fashion. Our results show that chicken cathelicidin-2 kills E. coli by permeabilizing the bacterial inner membrane and subsequently binds the outer membrane-derived lipoproteins and LPS to inhibit TLR2 and TLR4 activation, respectively. In addition, other cathelicidins, including human, mouse, pig, and dog cathelicidins, which lack antimicrobial activity under cell culture conditions, only inhibit macrophage activation by nonviable E. coli In total, this study shows that cathelicidins do not affect immune activation by viable bacteria and only inhibit inflammation when bacterial viability is lost. Therefore, cathelicidins provide a novel mechanism by which the immune system can discriminate between viable and nonviable Gram-negative bacteria to tune the immune response, thereby limiting collateral damage to the host and the risk for sepsis.

CATH-2 and LL-37 increase mannose receptor expression, antigen presentation and the endocytic capacity of chicken mononuclear phagocytes

Cathelicidins display in vitro and in vivo immunomodulatory activities and are part of the innate immune system. Previously, we found that in ovo treatment with chicken cathelicidin CATH-2 partially protects young broilers against respiratory E. coli infection. To determine the cellular aspects of this protection, we investigated immunomodulatory effects of CATH-2 and the human cathelicidin LL-37 on primary chicken peripheral blood mononuclear cells (PBMCs). Treatment of chicken PBMCs with L-CATH-2, D-CATH-2 or LL-37 increased the percentage of mononuclear phagocytes, but decreased that of B cells. L-CATH-2, D-CATH-2 and LL-37 treatment of chicken PBMCs also enhanced the expression levels of mannose receptor MRC1 and antigen presentation markers MHCII, CD40 and CD86 on mononuclear phagocytes, indicating increased antigen presentation capacity. Concomitantly, L-CATH-2, D-CATH-2 and LL-37 neutralized LPS-induced cytokine production, while increasing the endocytic capacity. We conclude that L-CATH-2, D-CATH-2 and LL-37 can modulate the immune response of primary chicken immune cells by increasing mannose receptor expression, antigen presentation, endocytosis and neutralizing LPS-induced cytokine production and as a result augment activation of the adaptive immune system.

LL37:DNA complexes provide antimicrobial activity against intracellular bacteria in human macrophages

As part of the innate host response neutrophils release neutrophil extracellular traps (NETs), protein:DNA complexes that contain a number of antimicrobial peptides (AMPs), such as cathelicidin. Human cathelicidin in its active form, LL37, has potent antimicrobial activity against bacteria. However, whether LL37 derived from NETs contributes to antimicrobial activity against intracellular pathogens remains unclear. Here, we report that NETs induced by mycobacteria contain cathelicidin. Human macrophages internalized NET-bound cathelicidin, which is transported to lysosomal compartments. Furthermore, using a model of in vitro-generated LL37:DNA complexes we found that LL37 derived from such complexes attacks mycobacteria in macrophage phagolysosomes resulting in antimicrobial activity. Taken together, our results suggest a mechanism by which LL37 in complex with DNA contributes to host defence against intracellular bacteria in human macrophages.

Differential Ability of Bovine Antimicrobial Cathelicidins to Mediate Nucleic Acid Sensing by Epithelial Cells

Cathelicidins encompass a family of cationic peptides characterized by antimicrobial activity and other functions, such as the ability to enhance the sensing of nucleic acids by the innate immune system. The present study aimed to investigate the ability of the bovine cathelicidins indolicidin, bactenecin (Bac)1, Bac5, bovine myeloid antimicrobial peptide (BMAP)-27, BMAP-28, and BMAP-34 to inhibit the growth of bacteria and to enhance the sensing of nucleic acid by the host’s immune system. BMAP-27 was the most effective at killing Staphylococcus aureus, Streptococcus uberis, and Escherichia coli, and this was dependent on its amphipathic structure and cationic charge. Although most cathelicidins possessed DNA complexing activity, only the alpha-helical BMAP cathelicidins and the cysteine-rich disulfide-bridged Bac1 were able to enhance the sensing of nucleic acids by primary epithelial cells. We also compared these responses with those mediated by neutrophils. Activation of neutrophils with phorbol myristate acetate resulted in degranulation and release of cathelicidins as well as bactericidal activity in the supernatants. However, only supernatants from unstimulated neutrophils were able to promote nucleic acid sensing in epithelial cells. Collectively, the present data support a role for certain bovine cathelicidins in helping the innate immune system to sense nucleic acids. The latter effect is observed at concentrations clearly below those required for direct antimicrobial functions. These findings are relevant in development of future strategies to promote protection at mucosal surfaces against pathogen invasion.

Interspecies cathelicidin comparison reveals divergence in antimicrobial activity, TLR modulation, chemokine induction and regulation of phagocytosis

Cathelicidins are short cationic peptides initially described as antimicrobial peptides, which can also modulate the immune system. Because most findings have been described in the context of human LL-37 or murine CRAMP, or have been investigated under varying conditions, it is unclear which functions are cathelicidin specific and which functions are general cathelicidin properties. This study compares 12 cathelicidins from 6 species under standardized conditions to better understand the conservation of cathelicidin functions. Most tested cathelicidins had strong antimicrobial activity against E. coli and/or MRSA. Interestingly, while more physiological culture conditions limit the antimicrobial activity of almost all cathelicidins against E. coli, activity against MRSA is enhanced. Seven out of 12 cathelicidins were able to neutralize LPS and another 7 cathelicidins were able to neutralize LTA; however, there was no correlation found with LPS neutralization. In contrast, only 4 cathelicidins enhanced DNA-induced TLR9 activation. In conclusion, these results provide new insight in the functional differences of cathelicidins both within and between species. In addition, these results underline the importance not to generalize cathelicidin functions and indicates that caution should be taken in extrapolating results from LL-37- or CRAMP-related studies to other animal settings.

Localization and developmental expression of two chicken host defense peptides: cathelicidin-2 and avian β-defensin 9

In the first weeks of life young chickens are highly susceptible to infectious diseases due to immaturity of the immune system. Little is known about the expression of host defense peptides (HDPs) during this period. In this study we examined the expression pattern of two chicken HDPs, the cathelicidin CATH-2 and the β-defensin AvBD9 by immunohistochemistry in a set of organs from embryonic day 12 until four weeks posthatch. AvBD9 was predominantly found in enteroendocrine cells throughout the intestine, the first report of in vivo HDP expression in this cell type, and showed stable expression levels during development. CATH-2 was exclusively found in heterophils which decreased after hatch in most of the examined organs including spleen, bursa and small intestine. In the lung CATH-2 expression was biphasic and peaked at the first day posthatch. In short, CATH-2 and AvBD9 appear to be expressed in cell types strategically located to respond to infectious stimuli, suggesting these peptides play a role in embryonic and early posthatch defense.

Protective effect of in ovo treatment with the chicken cathelicidin analog D-CATH-2 against avian pathogenic E. coli

Increasing antibiotic resistance and ever stricter control on antibiotic use are a driving force to develop alternatives to antibiotics. One such strategy is the use of multifunctional Host Defense Peptides. Here we examined the protective effect of prophylactic treatment with the D analog of chicken cathelicidin-2 (D-CATH-2) against a respiratory E. coli infection. Chickens were treated with D-CATH-2 in ovo at day 18 of embryonic development or intramuscularly at days 1 and 4 after hatch. At 7 days of age, birds were challenged intratracheally with avian pathogenic E. coli. Protection was evaluated by recording mortality, morbidity (Mean Lesion Score) and bacterial swabs of air sacs at 7 days post-infection. In ovo D-CATH-2 treatment significantly reduced morbidity (63%) and respiratory bacterial load (>90%), while intramuscular treatment was less effective. D-CATH-2 increased the percentage of peripheral blood lymphocytes and heterophils by both administration routes. E. coli specific IgM levels were lower in in ovo treated animals compared to intramuscular D-CATH-2 treatment. In short, in ovo treatment with the Host Defense Peptide derived D-CATH-2 can partially protect chickens from E. coli infection, making this peptide an interesting starting point to develop alternatives to antibiotics for use in the poultry sector.