IV. Paneth cell antimicrobial peptides and the biology of the mucosal barrier

Identification of Mycobacterium avium genes associated with resistance to host antimicrobial peptides

Antimicrobial peptides are an important component of the innate immune defence. Mycobacterium avium subsp. hominissuis (M. avium) is an organism that establishes contact with the respiratory and gastrointestinal mucosa as a necessary step for infection. M. avium is resistant to high concentrations of polymyxin B, a surrogate for antimicrobial peptides. To determine gene-encoding proteins that are associated with this resistance, we screened a transposon library of M. avium strain 104 for susceptibility to polymyxin B. Ten susceptible mutants were identified and the inactivated genes sequenced. The great majority of the genes were related to cell wall synthesis and permeability. The mutants were then examined for their ability to enter macrophages and to survive macrophage killing. Three clones among the mutants had impaired uptake by macrophages compared with the WT strain, and all ten clones were attenuated in macrophages. The mutants were also shown to be susceptible to cathelicidin (LL-37), in contrast to the WT bacterium. All but one of the mutants were significantly attenuated in mice. In conclusion, this study indicated that the M. avium envelope is the primary defence against host antimicrobial peptides.

Immune modulation effect of porcine placenta extracts in weaned the pig

In a previous study, we established a collection of appropriate porcine placental extracts using PBS at 80°C (PE-PBS80) as a food supplement to increase immune activities in a mice model. In this study, piglets were treated with 0.1%, 0.3%, and 0.5% PE-PBS80 for 3 wk after weaning. Experiments were performed at 2 separate farms using 2 different pig varieties. Composition of white blood cells, lymphocyte activation, and cytokine concentrations were analyzed to assess the immune modulation effect. In Exp. 1, the number of white blood cells increased significantly in the PE-PBS80 treatment and T- and B-cell activation increased as well (P < 0.01). Interestingly, piglets in all treatments in Exp. 2 were naturally infected by a rotavirus at the third day of the experiment but recovered after d 10. Increased lymphocyte activation was observed in the PE-PBS80 treatment (P < 0.01) regardless of viral infection. Additionally, unlike in Exp. 1, the percentage of granulocytes and concentrations of interferon-γ, IL-1β, and IgG increased in the PE-PBS80 treatment (P < 0.01) and were more active in the 0.3% PE-PBS80 treatment compared with the control and the other treatment. In conclusion, 0.3% PE-PBS80 treatment modulated immune activities in antigen-infected piglets. Therefore, the PE-PBS80 pig placental extract, particularly the 0.3% supplement to the normal diet, could be useful as an alternative feed supplement to modulate immune activity during the early piglet period.

Strain-specific polymorphisms in Paneth cell α-defensins of C57BL/6 mice and evidence of vestigial myeloid α-defensin pseudogenes

Paneth cells at the base of small intestinal crypts secrete microbicidal α-defensins, termed cryptdins (Crps) in mice, as mediators of innate immunity. Proteomic studies show that five abundant Paneth cell α-defensins in C57BL/6 mice are strain specific in that they have not been identified in other inbred strains of mice. Two C57BL/6-specific peptides are coded for by the Defcr20 and -21 genes evident in the NIH C57BL/6 genome but absent from the Celera mixed-strain assembly, which excludes C57BL/6 data and differs from the NIH build with respect to the organization of the α-defensin gene locus. Conversely, C57BL/6 mice lack the Crp1, -2, -4, and -6 peptides and their corresponding Defcr1, -2, -4, and -6 genes, which are common to several mouse strains, including those of the Celera assembly. In C57BL/6 mice, α-defensin gene diversification appears to have occurred by tandem duplication of a multigene cassette that was not found in the mixed-strain assembly. Both mouse genome assemblies contain conserved α-defensin pseudogenes that are closely related to functional myeloid α-defensin genes in the rat, suggesting that the neutrophil α-defensin defect in mice resulted from progressive gene loss. Given the role of α-defensins in shaping the composition of the enteric microflora, such polymorphisms may influence outcomes in mouse models of disease or infection.

Campylobacter capsule and lipooligosaccharide confer resistance to serum and cationic antimicrobials

The innate immune system plays a critical role in host defense against mucosal bacteria. Campylobacter jejuni is a major cause of human gastroenteritis that usually resolves spontaneously within several days, suggesting that innate mechanisms are important to control the infection. However, the specific means by which this occurs is not well understood. While diarrheal isolates of C. jejuni usually are susceptible to human serum, we found that a systemic strain of C. jejuni, isolated from the cerebrospinal fluid of an infant with meningitis, is relatively more resistant to human serum, the Bactericidal/Permeability-Increasing Protein (BPI), an endogenous cationic antimicrobial protein, and the cationic peptide antibiotic polymyxin B. To test the hypothesis that the surface properties of this strain contributed to its ability to withstand these innate host defenses, we constructed isogenic mutants in capsule (kpsM) and lipooligosaccharide (waaF) and complemented these mutants by insertion of the complementation construct in trans into hipO, a chromosomal locus. We found that capsule expression was essential for serum resistance, whereas lipooligosaccharide played no substantial role. In contrast, the lipooligosaccharide mutant showed increased sensitivity to polymyxin B, α-defensins, cathelicidins, and BPI. These findings suggest that the polysaccharides of C. jejuni strains contribute differently to resistance against host innate immunity; whereby capsule is more important for resisting human complement and lipooligosaccharide is more important for protection against killing mediated by cationic antimicrobial peptides and proteins.

Mucosal control of the intestinal microbial community

Although the knowledge of the effects of bacterial colonization on the immune system is rapidly expanding, surprisingly little is known about the immunological mechanisms that shape the intestinal microbial community. Specifically, the complexity of the intestinal microbiota and what constitutes a "healthy" microbial composition has only recently been addressed, facilitated by large-scale metagenomic screens. Containment of such a vast number of different microbes requires tight regulation at the mucosal surface. While beneficial relationships must not be compromised, invading pathogenic bacteria must be dealt with in order to maintain homeostasis. In this review, we will address the latest insights into the role of the mucosal immune system in the control of the microbiota.

Influence of alemtuzumab on the intestinal Paneth cells and microflora in macaques

Alemtuzumab has been recently introduced for induction therapy in organ transplantation. However, the pathogenesis and molecular mechanism of the impact of such induction therapy on bacterial infections remain to be clarified. We found the alterations of Paneth cells including abnormal Paneth cell granules and expression of lysozyme and defensin 5 in response to lymphocyte depletion by alemtuzumab. Lymphocyte depletion resulted in decreased expression of TNF-alpha, IFN-gamma, IL-10 and TGF-beta in the intestine. The diversity of gut bacteria varied significantly between different times of alemtuzumab treatment. Abnormal expression of granule peptides might result in impairment of host gut microflora. The alterations in bacterial microflora had almost reversed 56days after alemtuzumab treatment, which was consistent with our results that Paneth cells were recovered to secrete antimicrobial peptides to govern gut microflora. These findings indicated the associations between changes of Paneth cell function and gut microflora and supported the important role of Paneth cells to barrier impairment with the use of alemtuzumab in organ transplantation.

Anionic amino acids near the pro-alpha-defensin N terminus mediate inhibition of bactericidal activity in mouse pro-cryptdin-4

In mouse Paneth cells, alpha-defensins, termed cryptdins (Crps), are activated by matrix metalloproteinase-7-mediated proteolysis of inactive precursors (pro-Crps) to bactericidal forms. The activating cleavage step at Ser(43) downward arrow Ile(44) in mouse pro-Crp4-(20-92) removes nine acidic amino acids that collectively block the membrane-disruptive behavior of the Crp4 moiety of the proform. This inhibitory mechanism has been investigated further to identify whether specific cluster(s) of electronegative amino acids in pro-Crp4-(20-43) are responsible for blocking bactericidal activity and membrane disruption. To test whether specific cluster(s) of electronegative amino acids in pro-Crp4-(20-43) have specific positional effects that block bactericidal peptide activity and membrane disruption, acidic residues positioned at the distal (Asp(20), Asp(26), Glu(27), and Glu(28)), mid (Glu(32) and Glu(33)), and proximal (Glu(37), Glu(38), and Asp(39)) clusters in pro-Crp4-(20-92) were mutagenized, and variants were assayed for differential effects of mutagenesis on bactericidal peptide activity. Substitution of the mid and proximal Asp and Glu clusters with Gly produced additive effects with respect to the induction of both bactericidal activity and membrane permeabilization of live Escherichia coli ML35 cells. In contrast, substitution of distal Glu and Asp residues with Gly or their deletion resulted in pro-Crp4-(20-92) variants with bactericidal and membrane-disruptive activities equal to or greater than that of fully mature Crp4. These findings support the conclusion that the most distal N-terminal anionic residues of pro-Crp4-(20-92) are primarily responsible for blocking Crp4-mediated membrane disruption in the precursor.

Interactions of the intestinal epithelium with the pathogen and the indigenous microbiota: a three-way crosstalk

The mucosal surfaces of the gastrointestinal tract harbor a vast number of commensal microbiota that have coevolved with the host, and in addition display one of the most complex relationships with the host. This relationship affects several important aspects of the biology of the host including the synthesis of nutrients, protection against infection, and the development of the immune system. On the other hand, despite the existence of several lines of mucosal defense mechanisms, pathogenic organisms such as Shigella and Salmonella have evolved sophisticated virulence strategies for breaching these barriers. The constant challenge from these pathogens and the attempts by the host to counter them set up a dynamic equilibrium of cellular and molecular crosstalk. Even slight perturbations in this equilibrium may be detrimental to the host leading to severe bacterial infection or even autoimmune diseases like inflammatory bowel disease. Several experimental model systems, including germ-free mice and antibiotic-treated mice, have been used by various researchers to study this complex relationship. Although it is only the beginning, it promises to be an exciting era in the study of these host-microbe relationships.

Structure-dependent functional properties of human defensin 5

The mucosal epithelium secretes a variety of antimicrobial peptides that act as part of the innate immune system to protect against invading microbes. Here, we describe the functional properties of human defensin (HD) 5, the major antimicrobial peptide produced by Paneth cells in the ileum, in relation to its structure. The antimicrobial activity of HD-5 against Escherichia coli proved to be independent of its structure, whereas the unstructured peptide showed greatly reduced antimicrobial activity against Staphylococcus aureus. We find that HD-5 binds to the cell membrane of intestinal epithelial cells and induced secretion of the chemokine interleukin (IL)-8 in a concentration- and structure-dependent fashion. Incubation of HD-5 in the presence of tumor necrosis factor alpha further increased IL-8 secretion synergistically, suggesting that HD-5 may act as a regulator of the intestinal inflammatory response.

Role of the innate immune system and host-commensal mutualism

Host organisms live in intimate contact with indigenous microflora. The interactions between the host and commensal microbiota are highly complex and heterogeneous. A growing body of evidence indicates that commensal symbionts provide many benefits to the host physiology, particularly in the gastrointestinal system. The molecular mechanisms of the mutualistic interactions between the host and commensals are largely unknown but can be due either to bioactivity of the commensals or to the reaction of the host immune system to the commensal-derived products. Recent advances in our understanding of the innate immune system allow re-evaluation of some of the older findings regarding the mechanisms of benefits conferred by microflora. Here we review the examples of the benefits of host-commensal interactions that are due to recognition of commensal microbial products by the host innate immune system.

The front line of enteric host defense against unwelcome intrusion of harmful microorganisms: mucins, antimicrobial peptides, and microbiota

The intestinal tract is a complex ecosystem that combines resident microbiota and the cells of various phenotypes with complex metabolic activities that line the epithelial wall. The intestinal cells that make up the epithelium provide physical and chemical barriers that protect the host against the unwanted intrusion of microorganisms that hijack the cellular molecules and signaling pathways of the host and become pathogenic. Some of the organisms making up the intestinal microbiota also have microbicidal effects that contribute to the barrier against enteric pathogens. This review describes the two cell lineages present in the intestinal epithelium: the goblet cells and the Paneth cells, both of which play a pivotal role in the first line of enteric defense by producing mucus and antimicrobial peptides, respectively. We also analyze recent insights into the intestinal microbiota and the mechanisms by which some resident species act as a barrier to enteric pathogens. Moreover, this review examines whether the cells producing mucins or antimicrobial peptides and the resident microbiota act in partnership and whether they function individually and/or synergistically to provide the host with an effective front line of defense against harmful enteric pathogens.

Identification of novel genes in intestinal tissue that are regulated after infection with an intestinal nematode parasite

Infection of resistant or susceptible mice with Trichuris muris provokes mesenteric lymph node responses which are polarized towards Th2 or Th1, respectively. These responses are well documented in the literature. In contrast, little is known about the local responses occurring within the infected intestine. Through microarray analyses, we demonstrate that the gene expression profile of infected gut tissue differs according to whether the parasite is expelled or not. Genes differentially regulated postinfection in resistant BALB/c mice include several antimicrobial genes, in particular, intelectin (Itln). In contrast, analyses in AKR mice which ultimately progress to chronic infection provide evidence for a Th1-dominated mucosa with up-regulated expression of genes regulated by gamma interferon. Increases in the expression of genes associated with tryptophan metabolism were also apparent with the coinduction of tryptophanyl tRNA synthetase (Wars) and indoleamine-2,3-dioxygenase (Indo). With the emerging literature on the role of these gene products in the suppression of T-cell responses in vitro and in vivo, their up-regulated expression here may suggest a role for tryptophan metabolism in the parasite survival strategy.

Mouse paneth cell secretory responses to cell surface glycolipids of virulent and attenuated pathogenic bacteria

Mouse Paneth cells respond to bacteria and bacterial cell surface antigens by discharging secretory granules into the lumen of small intestinal crypts (T. Ayabe et al., Nat. Immunol. 1:113-118, 2000). To investigate mechanisms regulating these responses, purified surface glycolipid molecules with known acyl chain modifications and attenuated properties were tested for the ability to stimulate Paneth cell secretion. The antigens included lipopolysaccharide (LPS) from wild-type and msbB-null Escherichia coli and phoP-null and phoP-constitutive Salmonella enterica serovar Typhimurium strains, as well as LPS, lipid A, and lipoteichoic acid from Pseudomonas aeruginosa and Listeria monocytogenes grown in Mg2+-limited media. Measurements of total secreted protein, secreted lysozyme, and the bactericidal peptide activities of collected secretions showed that the purified antigens elicited similar secretory responses from Paneth cells in mouse crypts ex vivo, regardless of glycolipid acyl chain modification. Despite their impaired Tlr4 pathway, Paneth cells in ex vivo C3H/HeJ mouse crypts released equivalent amounts of bactericidal peptide activity in response to purified bacterial antigens, including lipid A. Thus, mouse Paneth cells respond equivalently to purified bacterial cell envelope glycolipids, regardless of functional Tlr4, the structural properties of glycolipid acyl chains, or their association with virulence in humans.

Events at the host-microbial interface of the gastrointestinal tract. I. Adaptation to a microbial world: role of epithelial bactericidal/permeability-increasing protein

Epithelial cells of many mucosal organs have adapted to coexist with microbes and microbial products. In general, most studies suggest that epithelial cells benefit from interactions with commensal microorganisms present at the lumenal surface. However, potentially injurious molecules found in this microenvironment also have the capacity to elicit local inflammatory responses and even systemic disease. In this environment, the epithelium has evolved effective mechanisms to cope with microbial products and to provide appropriate responses to potential pathogens. Although our understanding of these mechanisms is clearly in its infancy, a number of recent findings provide insight into phenotypic characteristics that allow for this discrimination. Here, we briefly review some of these mechanisms, with particular attention to epithelial expression of the anti-infective molecule bactericidal/permeability-increasing protein.

Antagonistic activities of lactobacilli and bifidobacteria against microbial pathogens

The gastrointestinal tract is a complex ecosystem that associates a resident microbiota and cells of various phenotypes lining the epithelial wall expressing complex metabolic activities. The resident microbiota in the digestive tract is a heterogeneous microbial ecosystem containing up to 1 x 10(14) colony-forming units (CFUs) of bacteria. The intestinal microbiota plays an important role in normal gut function and maintaining host health. The host is protected from attack by potentially harmful microbial microorganisms by the physical and chemical barriers created by the gastrointestinal epithelium. The cells lining the gastrointestinal epithelium and the resident microbiota are two partners that properly and/or synergistically function to promote an efficient host system of defence. The gastrointestinal cells that make up the epithelium, provide a physical barrier that protects the host against the unwanted intrusion of microorganisms into the gastrointestinal microbiota, and against the penetration of harmful microorganisms which usurp the cellular molecules and signalling pathways of the host to become pathogenic. One of the basic physiological functions of the resident microbiota is that it functions as a microbial barrier against microbial pathogens. The mechanisms by which the species of the microbiota exert this barrier effect remain largely to be determined. There is increasing evidence that lactobacilli and bifidobacteria, which inhabit the gastrointestinal microbiota, develop antimicrobial activities that participate in the host's gastrointestinal system of defence. The objective of this review is to analyze the in vitro and in vivo experimental and clinical studies in which the antimicrobial activities of selected lactobacilli and bifidobacteria strains have been documented.

Peptide fragments of AMP-18, a novel secreted gastric antrum mucosal protein, are mitogenic and motogenic

Antrum mucosal protein (AMP)-18 is a novel 18-kDa protein synthesized by cells of the gastric antrum mucosa. The protein is present in secretion granules of murine gastric antrum epithelial cells and is a component of canine antrum mucus, suggesting that it is secreted into the viscoelastic gel layer on the mucosal surface. Release of the protein appears to be regulated because forskolin decreased the amount of immunoreactive AMP-18 in primary cultures of canine antrum mucosal epithelial cells, and indomethacin gavaged into the stomach of mice reduced AMP-18 content in antrum mucosal tissue before inducing histological injury. A functional domain of the protein was identified by preparing peptides derived from the center of human AMP-18. A 21-mer peptide stimulated growth of gastric and intestinal epithelial cells, but not fibroblasts, and increased restitution of scrape-wounded gastric epithelial monolayers. These functions of AMP-18 suggest that its release onto the apical cell surface is regulated and that the protein and/or peptide fragments may protect the antral mucosa and promote healing by facilitating restitution and proliferation after injury.

Molecular features of adult mouse small intestinal epithelial progenitors

The adult mouse small intestinal epithelium undergoes perpetual regeneration, fueled by a population of multipotential stem cells and oligopotential daughters located at the base of crypts of Lieberkühn. Although the morphologic features of small intestinal epithelial progenitors (SiEPs) are known, their molecular features are poorly defined. Previous impediments to purification and molecular characterization of SiEPs include lack of ex vivo clonigenic assays and the difficulty of physically retrieving them from their niche where they are interspersed between their numerous differentiated Paneth cell daughters. To overcome these obstacles, we used germ-free transgenic mice lacking Paneth cells to obtain a consolidated population of SiEPs with normal proliferative activity. These cells were harvested by laser capture microdissection. Functional genomics analysis identified 163 transcripts enriched in SiEPs compared with Paneth cell-dominated normal crypt base epithelium. The dataset was validated by (i) correlation with the organellar composition of SiEPs versus Paneth cells, (ii) similarities to databases generated from recent mouse hematopoietic and neural stem cell genome anatomy projects, and (iii) laser capture microdissectionreal-time quantitative RT-PCR studies of progenitor cell-containing populations retrieved from the small intestines, colons, and stomachs of conventionally raised mice. The SiEP profile has prominent representation of genes involved in c-myc signaling and in the processing, localization, and translation of mRNAs. This dataset, together with our recent analysis of gene expression in the gastric stem cell niche, discloses a set of molecular features shared by adult mouse gut epithelial progenitors.

Expression of calnexin reflects paneth cell differentiation and function

It has been suggested that the behavior and function of Paneth cells in metaplasia are different from those found in normal intestinal mucosa. In this study, we investigated whether calnexin, a protein involved in secretory pathways, might be associated with differentiation and function of Paneth cells in normal small intestine, in complete intestinal metaplasia of the stomach, and in Paneth cell-rich adenomas. Differentiation and function of Paneth cells was monitored by Ki67, lysozyme, and morphologic features. Using a newly established monoclonal antibody, we found that calnexin is regularly synthesized by Paneth cells of normal small intestine. In these cells, the staining intensity of calnexin was inversely correlated with their content of secretory granules (lysozyme). In contrast, Paneth cells of intestinal metaplasia and Paneth cell-rich adenomas showed a reduced immunostaining of both calnexin and lysozyme. Moreover, these Paneth cells synthesized the proliferation marker Ki67, a phenomenon that was never observed in Paneth cells of normal small intestine. In vitro experiments using CaCo2 cells showed that the expression of calnexin is not directly affected by the induction of mitosis. In conclusion, calnexin probably reflects the status of Paneth cell differentiation and function. The results do not necessarily indicate that calnexin has a function in Paneth cell proliferation.

The host-microbe interface within the gut

Colonization with bacteria is critical for the normal structural and functional development and optimal function of the mucosal immune system. Unrestrained mucosal immune activation in response to bacterial signals from the lumen is, however, a risk factor for inflammatory bowel disease. Therefore, mucosal immune responses to indigenous flora require precise control and an immunosensory capacity for distinguishing commensals from pathogens. The use of germ-free animal models with selective colonization strategies combined with modern molecular techniques promises to clarify the molecular signals responsible for host-flora interactions in health and disease. At least half of the resident flora cannot be cultured by conventional techniques but are identifiable by molecular methods. Collectively, the resident flora represent a virtual organ with a metabolic activity in excess of the liver and a microbiome in excess of the human genome. An improved understanding of this hidden organ holds secrets relevant to several infectious, inflammatory and neoplastic disease mechanisms.

Lipid mediator-induced expression of bactericidal/ permeability-increasing protein (BPI) in human mucosal epithelia

Epithelial cells which line mucosal surfaces are the first line of defense against bacterial invasion and infection. Recent studies have also indicated that epithelial cells contribute significantly to the orchestration of ongoing inflammatory processes. Here, we demonstrate that human epithelial cells express bactericidal/permeability-increasing protein (BPI), an antibacterial and endotoxin-neutralizing molecule previously associated with neutrophils. Moreover, we demonstrate that such BPI expression is transcriptionally regulated by analogs of endogenously occurring anti-inflammatory eicosanoids (aspirin-triggered lipoxins, ATLa). Initial studies to verify microarray analysis revealed that epithelial cells of wide origin (oral, pulmonary, and gastrointestinal mucosa) express BPI and each is similarly regulated by aspirin-triggered lipoxins. Studies aimed at localization of BPI revealed that such expression occurs on the cell surface of cultured epithelial cell lines and dominantly localizes to epithelia in human mucosal tissue. Functional studies employing a BPI-neutralizing anti-serum revealed that surface BPI blocks endotoxin-mediated signaling in epithelia and kills Salmonella typhimurium. These studies identify a previously unappreciated "molecular shield" for protection of mucosal surfaces against Gram-negative bacteria and their endotoxin.

Phenotypic and genomic analyses of the Mycobacterium avium complex reveal differences in gastrointestinal invasion and genomic composition

Mycobacterium avium and Mycobacterium intracellulare are closely related organisms and comprise the Mycobacterium avium complex. These organisms share many common characteristics, including the ability to cause life-threatening respiratory infections in people with underlying lung pathology or immunological defects and occasionally in those with no known predisposing conditions. However, the ability to invade the mucosa of the gastrointestinal tract and cause disseminated disease in AIDS patients has not been epidemiologically linked to M. intracellulare and appears to be unique to M. avium. We compared the abilities of M. avium and M. intracellulare to tolerate the acidic conditions of the stomach, to resist the membrane-disrupting activity of cationic peptides, and to invade intestinal epithelial cells in vitro and in vivo. We observed that M. avium and M. intracellulare were both tolerant to the acidic conditions encountered in the stomach and resistant to cationic peptides. However, when strains of M. avium and M. intracellulare were examined for their ability to enter cultured human intestinal cells or mouse intestinal mucosa, we observed that M. avium could invade more efficiently than M. intracellulare. To elucidate the basis of this pathogenic difference and identify genes involved in the invasion of the intestinal mucosa, we performed chromosomal DNA subtractive hybridization using M. avium and M. intracellulare chromosomal DNAs. In all, 21 genes that were present in M. avium but absent in M. intracellulare were identified, including some that may be associated with the ability of M. avium to invade the intestinal mucosa.

Antimycobacterial agent based on mRNA encoding human beta-defensin 2 enables primary macrophages to restrict growth of Mycobacterium tuberculosis

Human macrophages are hosts for Mycobacterium tuberculosis, the causative agent of tuberculosis, which killed approximately 1.87 million people in 1997. Human alveolar macrophages do not express alpha- or beta-defensins, broad-spectrum antimicrobial peptides which are expressed in macrophages from other species more resistant to infection with M. tuberculosis. It has been previously reported that M. tuberculosis is susceptible to killing by defensins, which may explain the difference in resistance. Defensin peptides have been suggested as a possible therapeutic strategy for a variety of infectious diseases, but development has been hampered by difficulties in their large-scale production. Here we report the cellular synthesis of human beta-defensin 2 via highly efficient mRNA transfection of human macrophages. This enabled mycobactericidal and mycobacteristatic activity by the macrophages. Although human macrophages are difficult to transfect with plasmid vectors, these studies illustrate that primary macrophages are permissive for mRNA transfection, which enabled expression of a potentially therapeutic protein.

Cryptdin-3 induces novel apical conductance(s) in Cl- secretory, including cystic fibrosis, epithelia

Opening of anion-conductive pathways in apical membranes of secretory cells lining mucosal surfaces is a critical step in salt and water secretion and, thus, hydration of sites including airway and intestine. In intestine, Paneth cells are positioned at the base of the secretory gland (crypt) and release defensin peptide, in mice termed cryptdins, into the crypt lumen. Because at least some defensins have been shown to form anion-conductive channels in phospholipid bilayers, we tested whether these endogenous antimicrobial peptides could act as soluble inducers of channel-like activity when applied to apical membranes. To directly evaluate the possibility of cryptdin-3-mediated apical anion conductance (G(ap)), we have utilized amphotericin B to selectively permeabilize basolateral membranes of electrically tight monolayers of polarized human intestinal secretory epithelia (T84 cells), thus isolating the apical membrane for study. Cryptdin-3 induces G(ap) that is voltage independent (deltaG(ap) = 1.90 +/- 0.60 mS/cm2) and exhibits ion selectivity contrasting to that elicited by forskolin or thapsigargin (for cryptdin-3, Cl- = gluconate; for forskolin and thapsigargin, Cl- >> gluconate). We cannot exclude the possibility that the macroscopic current induced by cryptdin could be the sum of cation and Cl- currents. Cryptdin-3 induces a current in basolaterally permeabilized epithelial monolayers derived from airway cells harboring the deltaF508 mutation of cystic fibrosis (CF; deltaG(ap) = 0.80 +/- 0.06 mS/cm2), demonstrating that cryptdin-3 restores anion secretion in CF cells; this occurs independently of the CF transmembrane conductance regulator channel. These results support the idea that cryptdin-3 may associate with apical membranes of Cl--secreting epithelia and self-assemble into conducting channels capable of mediating a physiological response.

Salivary histatin 5 and human neutrophil defensin 1 kill Candida albicans via shared pathways

Salivary histatins are a family of basic histidine-rich proteins in which therapeutic potential as drugs against oral candidiasis is apparent, considering their potent in vitro antifungal activity and lack of toxicity to humans. Histatin 5 (Hst 5) kills the fungal pathogen Candida albicans via a mechanism that involves binding to specific sites on the yeast cell membrane and subsequent release of cellular ATP in the absence of cytolysis. We explored the killing pathway activated by Hst 5 and compared it to those activated by other antifungal agents. The candidacidal activity of human neutrophil defensin 1 (HNP-1) shared very similar features to Hst 5 cytotoxic action with respect to active concentrations and magnitude of induction of nonlytic ATP efflux, depletion of intracellular ATP pools, and inhibitor profile. Hst 5 and HNP-1 are basic proteins of about 3 kDa; however, they have unique primary sequences and solution structures that cannot explain how these two molecules act so similarly on C. albicans to induce cell death. Our finding that HNP-1 prevented Hst 5 binding to the candidal Hst 5 binding protein suggests that the basis for the overlapping actions of these two naturally occurring antimicrobial proteins may involve interactions with shared yeast components.