With the rapid rise in the incidence of multidrug resistant infections, there is substantial interest in host defense peptides as templates for production of new antimicrobial therapeutics. Natural peptides are multifunctional mediators of the innate immune response, with some direct antimicrobial activity and diverse immunomodulatory properties. We have previously developed an innate defense regulator (IDR) 1, with protective activity against bacterial infection mediated entirely through its effects on the immunity of the host, as a novel approach to anti-infective therapy. In this study, an immunomodulatory peptide IDR-1002 was selected from a library of bactenecin derivatives based on its substantially more potent ability to induce chemokines in human PBMCs. The enhanced chemokine induction activity of the peptide in vitro correlated with stronger protective activity in vivo in the Staphylococcus aureus-invasive infection model, with a >5-fold reduction in the protective dose in direct comparison with IDR-1. IDR-1002 also afforded protection against the Gram-negative bacterial pathogen Escherichia coli. Chemokine induction by IDR-1002 was found to be mediated through a Gi-coupled receptor and the PI3K, NF-κB, and MAPK signaling pathways. The protective activity of the peptide was associated with in vivo augmentation of chemokine production and recruitment of neutrophils and monocytes to the site of infection. These results highlight the importance of the chemokine induction activity of host defense peptides and demonstrate that the optimization of the ex vivo chemokine-induction properties of peptides is a promising method for the rational development of immunomodulatory IDR peptides with enhanced anti-infective activity.

A fundamentally new strategy for the treatment of infectious disease is the modulation of host immune responses to enhance clearance of infectious agents and reduce tissue damage due to inflammation. Antimicrobial host defense peptides have been investigated for their potential as a new class of antimicrobial drugs. Recently their immunomodulatory activities have begun to be appreciated. Modulation of innate immunity by synthetic variants of host defense peptides, called innate defense regulators (IDRs), is protective without direct antimicrobial action. We discuss the potential and current limitations in exploiting the immunomodulatory activity of IDRs as a novel anti-infective pathway. IDRs show significant promise and current research is uncovering mechanistic information that will aid in the future development of IDRs for clinical use.

Innate immunity is triggered by a variety of bacterial molecules, resulting in both protective and potentially harmful pro-inflammatory responses. Further, innate immunity also provides a mechanism for the maintenance of homeostasis between the host immune system and symbiotic or non-pathogenic microorganisms. However, the bacterial factors that mediate these protective effects have been incompletely defined. Here, it was demonstrated that the lantiobiotic nisin Z is able to modulate host immune responses and mediate protective host immunity. Nisin Z induced the secretion of the chemokines MCP-1, IL-8 and Gro-α, and significantly reduced TNF-α induction in response to bacterial LPS in human PBMC. The results correlated with the ability of nisin Z to confer protection against both the Gram-positive organism Staphylococcus aureus, and the Gram-negatives Salmonella enterica sv. Typhimurium and Escherichia coli in murine challenge models. Mechanistic studies revealed that nisin Z modulates host immunity through similar mechanisms as natural host defense peptides, engaging multiple signal transduction pathways and growth factor receptors. The results presented herein demonstrate that, in addition to nisin Z, other bacterial cationic peptides and, in particular, the lantibiotics, could represent a new class of secreted bacterial molecule with immunomodulatory activities.

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Moraxella catarrhalis is a gram-negative bacterium that is mainly responsible for respiratory tract infections. In this study we report a novel outer membrane protein (OMP), designated M35, with a molecular mass of 36.1 kDa. This protein was structurally homologous to classic gram-negative porins, such as OMP C from Escherichia coli and OMP K36 from Klebsiella pneumoniae, with a predicted structure of 8 surface loops and 16 antiparallel ␤-sheets. The DNA sequences of the genes from 18 diverse clinical isolates showed that the gene was highly conserved (99.6 to 100% of nucleotides), with only one isolate (ID78LN266) having base variations that resulted in amino acid substitutions. Electrophoresis and analysis of recognition of the protein using mouse anti-M35 sera showed that M35 was expressed on the bacterial surface and constitutively expressed across M. catarrhalis isolates, with only ID78LN266 showing poor antibody recognition. Our results showed that the single amino acid mutation in loop 3 significantly affected antibody recognition, indicating that loop 3 appeared to contain an immunodominant B-cell epitope. The antibody specificity to loop 3 may be a potential mechanism for evasion of host immune responses targeted to M35, since loop 3 should theoretically orientate into the porin channel. Thus, M35 is a highly conserved, surface-expressed protein that is of significance for its potential functional role as an M. catarrhalis porin and is of interest as a vaccine candidate.Moraxella catarrhalis, a gram-negative bacterium, is predominantly responsible for respiratory tract infections, such as otitis media, sinusitis, and exacerbations of chronic obstructive pulmonary disease (17,24,30). On rare occasions, it can also cause more serious diseases, such as meningitis and septicemia, although these occur mainly in immunocompromised populations and neonates (7, 23). M. catarrhalis pathogenesis and virulence factors are not well understood. For a long time, limited research was undertaken on this bacterium, since it was considered a normal commensal. The acceptance of M. catarrhalis as a pathogen, and its remarkably rapid development of resistance to ␤-lactam antibiotics (12,14), have stimulated research into the pathogenesis of infection and characterization of the bacterium.The majority of research into M. catarrhalis has been focused on the identification and characterization of outer membrane proteins (OMP), with a view to assessing their suitability as vaccine antigens. An ideal vaccine candidate should be highly conserved so that it can elicit an immune response that protects against all strains of the bacterium. A number of potential vaccine candidates have been identified so far, and one particular characteristic of these is conservation across strains. Two proteins that demonstrate potential as vaccine antigens, OMP E and OMP CD, appear to be well conserved (24-26) and demonstrate some similarity with porins from Escherichia coli and Pseudomonas species, respectively (24). This study reports the characte...