Borrelia peptidoglycan interacting Protein (BpiP) contributes to the fitness of Borrelia burgdorferi against host-derived factors and influences virulence in mouse models of Lyme disease.

The Peptidoglycan (PG) cell wall of the Lyme disease (LD) spirochete, Borrelia burgdorferi (Bb), contributes to structural and morphological integrity of Bb; is a persistent antigen in LD patients; and has a unique pentapeptide with L-Ornithine as the third amino acid that cross-links its glycan polymers. A borrelial homolog (BB_0167) interacted specifically with borrelilal PG via its peptidoglycan interacting motif (MHELSEKRARAIGNYL); was localized to the protoplasmic cylinder of Bb; and was designated as Borrelia peptidoglycan interacting Protein (BpiP). A bpiP mutant displayed no defect under in vitro growth conditions with similar levels of several virulence-related proteins. However, the burden of bpiP mutant in C3H/HeN mice at day 14, 28 and 62 post-infection was significantly lower compared to control strains. No viable bpiP mutant was re-isolated from any tissues at day 62 post-infection although bpiP mutant was able to colonize immunodeficient SCID at day 28 post-infection. Acquisition or transmission of bpiP mutant by Ixodes scapularis larvae or nymphs respectively, from and to mice, was significantly lower compared to control strains. Further analysis of bpiP mutant revealed increased sensitivity to vancomycin, osmotic stress, lysosomal extracts, human antimicrobial peptide cathelicidin-LL37, complement-dependent killing in the presence of day 14 post-infection mouse serum and increased internalization of CFSC-labeled bpiP mutant by macrophages and dendritic cells compared to control strains. These studies demonstrate the importance of accessory protein/s involved in sustaining integrity of PG and cell envelope during different phases of Bb infection.

The Lyme disease spirochete's BpuR DNA/RNA-binding protein is differentially expressed during the mammal-tick infectious cycle, which affects translation of the SodA superoxide dismutase.

When the Lyme disease spirochete, Borrelia burgdorferi, transfers from a feeding tick into a human or other vertebrate host, the bacterium produces vertebrate-specific proteins and represses factors needed for arthropod colonization. Previous studies determined that the B. burgdorferi BpuR protein binds to its own mRNA and autoregulates its translation, and also serves as co-repressor of erp transcription. Here, we demonstrate that B. burgdorferi controls transcription of bpuR, expressing high levels of bpuR during tick colonization but significantly less during mammalian infection. The master regulator of chromosomal replication, DnaA, was found to bind specifically to a DNA sequence that overlaps the bpuR promoter. Cultured B. burgdorferi that were genetically manipulated to produce elevated levels of BpuR exhibited altered levels of several proteins, although BpuR did not impact mRNA levels. Among these was the SodA superoxide dismutase, which is essential for mammalian infection. BpuR bound to sodA mRNA in live B. burgdorferi, and a specific BpuR-binding site was mapped 5' of the sodA open reading frame. Recognition of posttranscriptional regulation of protein levels by BpuR adds another layer to our understanding of the B. burgdorferi regulome, and provides further evidence that bacterial protein levels do not always correlate directly with mRNA levels.

Regulation of Gene and Protein Expression in the Lyme Disease Spirochete.

The infectious cycle of Borrelia burgdorferi necessitates persistent infection of both vertebrates and ticks, and efficient means of transmission between those two very different types of hosts. The Lyme disease spirochete has evolved mechanisms to sense its location in the infectious cycle, and use that information to control production of the proteins and other factors required for each step. Numerous components of borrelial regulatory pathways have been characterized to date. Their effects are being pieced together, thereby providing glimpses into a complex web of cooperative and antagonistic interactions. In this chapter, we present a broad overview of B. burgdorferi gene and protein regulation during the natural infectious cycle, discussions of culture-based methods for elucidating regulatory mechanisms, and summaries of many of the known regulatory proteins and small molecules. We also highlight areas that are in need of substantially more research.

The Borrelia burgdorferi Glycosaminoglycan Binding Protein Bgp in the B31 Strain Is Not Essential for Infectivity despite Facilitating Adherence and Tissue Colonization.

The Lyme disease-causing organism Borrelia burgdorferi is transmitted into the mammalian host by an infected-tick bite. Successful infection relies on the ability of this extracellular pathogen to persist and colonize different tissues. B. burgdorferi encodes a large number of adhesins that are able to interact with host ligands to facilitate adherence and tissue colonization. Multiple glycosaminoglycan binding proteins present in B. burgdorferi offer a degree of redundancy of function during infection, and this highlights the importance of glycosaminoglycans as host cell receptors for spirochete adherence. Of particular interest in this study is Borrelia glycosaminoglycan binding protein (Bgp), which binds to heparin-related glycosaminoglycans. The properties of a bgp transposon mutant and a trans-complemented derivative were compared to those of the wild-type B. burgdorferi in the in vitro binding assays and in infection studies using a C3H/HeJ mouse infection model. We determined that the loss of Bgp impairs spirochete adherence, infectivity, and tissue colonization, resulting in a reduction of inflammatory manifestations of Lyme disease. Although Bgp is not essential for infectivity, it is an important virulence factor of B. burgdorferi that allows adherence and tissue colonization and contributes to disease severity.

Coxiella burnetii Nine Mile phase I primary infection derived protective immunity against C. burnetii reinfection in mice depends on both B and T cells, but T cells play a critical role.

Coxiella burnetii is an obligate intracellular Gram-negative bacterium that causes acute and chronic Q fever in humans. Acute Q fever is usually a flu-like, self-limiting or treatable illness, but some infections can turn into a severe and sometimes fatal chronic disease. There is currently no FDA-approved vaccine available for the prevention of human Q fever in the US, development of a safe and effective vaccine for the prevention of human Q fever remains an important goal for public health. However, there is a fundamental gap in knowledge regarding the mechanism of protective immunity against C. burnetii infection. To understand the mechanism of C. burnetii infection induced protective immunity, we examined if C. burnetii Nine Mile phase I (NMI) infection induces protection against C. burnetii reinfection in mice. Our results indicate that NMI-infected mice conferred significant protection against C. burnetii reinfection. We also found that NMI infection derived protection did not depend on the routes of infection and antibodies are required for NMI infection derived protection. In addition, NMI infection elicited a comparable level of protection in Wild type, CD4+ T cell deficient, and CD8+ T cell deficient mice, partial protection in B cell deficient mice but no protection in T cell deficient mice. These results suggest that both B cells and T cells are required for NMI-infection derived protection, but T cells may play a critical role. Therefore, the new generation vaccine for the prevention of human Q fever should be focused on boosting both humoral and T cell immune responses.

Francisella DnaK inhibits tissue-nonspecific alkaline phosphatase.

Following pulmonary infection with Francisella tularensis, we observed an unexpected but significant reduction of alkaline phosphatase, an enzyme normally up-regulated following inflammation. However, no reduction was observed in mice infected with a closely related gram-negative pneumonic organism (Klebsiella pneumoniae) suggesting the inhibition may be Francisella-specific. In similar fashion to in vivo observations, addition of Francisella lysate to exogenous alkaline phosphatase (tissue-nonspecific isozyme) was inhibitory. Partial purification and subsequent proteomic analysis indicated the inhibitory factor to be the heat shock protein DnaK. Incubation with increasing amounts of anti-DnaK antibody reduced the inhibitory effect in a dose-dependent manner. Furthermore, DnaK contains an adenosine triphosphate binding domain at its N terminus, and addition of adenosine triphosphate enhances dissociation of DnaK with its target protein, e.g. alkaline phosphatase. Addition of adenosine triphosphate resulted in decreased DnaK co-immunoprecipitated with alkaline phosphatase as well as reduction of Francisella-mediated alkaline phosphatase inhibition further supporting the binding of Francisella DnaK to alkaline phosphatase. Release of DnaK via secretion and/or bacterial cell lysis into the extracellular milieu and inhibition of plasma alkaline phosphatase could promote an orchestrated, inflammatory response advantageous to Francisella.

Cellular and transcriptome signatures unveiled by single-cell RNA-Seq following ex vivo infection of murine splenocytes with Borrelia burgdorferi.

Introduction: Lyme disease, the most common tick-borne infectious disease in the US, is caused by a spirochetal pathogen Borrelia burgdorferi (Bb). Distinct host responses are observed in susceptible and resistant strains of inbred of mice following infection with Bb reflecting a subset of inflammatory responses observed in human Lyme disease. The advent of post-genomic methodologies and genomic data sets enables dissecting the host responses to advance therapeutic options for limiting the pathogen transmission and/or treatment of Lyme disease. Methods: In this study, we used single-cell RNA-Seq analysis in conjunction with mouse genomics exploiting GFP-expressing Bb to sort GFP+ splenocytes and GFP- bystander cells to uncover novel molecular and cellular signatures that contribute to early stages of immune responses against Bb. Results: These data decoded the heterogeneity of splenic neutrophils, macrophages, NK cells, B cells, and T cells in C3H/HeN mice in response to Bb infection. Increased mRNA abundance of apoptosis-related genes was observed in neutrophils and macrophages clustered from GFP+ splenocytes. Moreover, complement-mediated phagocytosis-related genes such as C1q and Ficolin were elevated in an inflammatory macrophage subset, suggesting upregulation of these genes during the interaction of macrophages with Bb-infected neutrophils. In addition, the role of DUSP1 in regulating the expression of Casp3 and pro-inflammatory cytokines Cxcl1, Cxcl2, Il1b, and Ccl5 in Bb-infected neutrophils were identified. Discussion: These findings serve as a growing catalog of cell phenotypes/biomarkers among murine splenocytes that can be exploited for limiting spirochetal burden to limit the transmission of the agent of Lyme disease to humans via reservoir hosts.

Antifungal activity of dendritic cell lysosomal proteins against Cryptococcus neoformans.

Cryptococcal meningitis is a life-threatening disease among immune compromised individuals that is caused by the opportunistic fungal pathogen Cryptococcus neoformans. Previous studies have shown that the fungus is phagocytosed by dendritic cells (DCs) and trafficked to the lysosome where it is killed by both oxidative and non-oxidative mechanisms. While certain molecules from the lysosome are known to kill or inhibit the growth of C. neoformans, the lysosome is an organelle containing many different proteins and enzymes that are designed to degrade phagocytosed material. We hypothesized that multiple lysosomal components, including cysteine proteases and antimicrobial peptides, could inhibit the growth of C. neoformans. Our study identified the contents of the DC lysosome and examined the anti-cryptococcal properties of different proteins found within the lysosome. Results showed several DC lysosomal proteins affected the growth of C. neoformans in vitro. The proteins that killed or inhibited the fungus did so in a dose-dependent manner. Furthermore, the concentration of protein needed for cryptococcal inhibition was found to be non-cytotoxic to mammalian cells. These data show that many DC lysosomal proteins have antifungal activity and have potential as immune-based therapeutics.

Pirfenidone regulates LPS mediated activation of neutrophils.

Excessive inflammation or its absence may result in impaired wound healing. Neutrophils are among the first innate immune cells to arrive at the injury site. They participate in infection control and debris removal to initiate healing. If not timely resolved, neutrophils can cause excessive tissue inflammation and damage. Drugs with anti-inflammatory and anti-fibrotic effects are of promise for improving healing by balancing the primary defensive functions and excessive tissue damage actions. Of interest, pirfenidone (Pf), an FDA approved anti-fibrotic drug to treat idiopathic pulmonary fibrosis, has been shown to ameliorate inflammation in several animal models including mouse deep partial-thickness burn wounds. However, there is a lack of mechanistic insights into Pf drug action on inflammatory cells such as neutrophils. Here, we examined the treatment effects of Pf on LPS-stimulated neutrophils as a model of non-sterile inflammation. Firstly, Pf reduced chemotaxis and production of pro-inflammatory ROS, cytokines, and chemokines by LPS-activated neutrophils. Secondly, Pf increased anti-inflammatory IL-1RA and reduced neutrophil degranulation, phagocytosis, and NETosis. Thirdly, Pf affected downstream signaling kinases which might directly or indirectly influence neutrophil responses to LPS. In conclusion, the results suggest that Pf lessens the inflammatory phenotypes of LPS-activated neutrophils.

Thioredoxin Modulates Cell Surface Hydrophobicity in Acinetobacter baumannii.

Acinetobacter baumannii, a Gram-negative coccobacillus, has become a prevalent nosocomial health threat affecting the majority of hospitals both in the U.S. and around the globe. Microbial cell surface hydrophobicity (CSH) has previously been correlated with virulence, uptake by immune cells, and attachment to epithelial cells. A mutant strain of A. baumannii (ΔtrxA) lacking the redox protein thioredoxin A was found to be more hydrophobic than its wild type (WT) and complemented counterparts, as measured by both Microbial Adhesion to Hydrocarbon (MATH) and salt aggregation. The hydrophobicity of the mutant could be abrogated through treatment with sodium cyanoborohydride (SCBH). This modulation correlated with reduction of disulfide bonds, as SCBH was able to reduce 5,5'-dithio-bis-[2-nitrobenzoic acid] and treatment with the known disulfide reducer, ß-mercaptoethanol, also decreased ΔtrxA CSH. Additionally, the ΔtrxA mutant was more readily taken up than WT by J774 macrophages and this differential uptake could be abrogated though SCBH treatment. When partitioned into aqueous and hydrophobic phases, ΔtrxA recovered from the hydrophobic partition was phagocytosed more readily than from the aqueous phase further supporting the contribution of CSH to A. baumannii uptake by phagocytes. A second Gram-negative bacterium, Francisella novicida, also showed the association of TrxA deficiency (FnΔtrxA) with increased hydrophobicity and uptake by J774 cells. We previously have demonstrated that modification of the type IV pilus system (T4P) was associated with the A. baumannii ΔtrxA phenotype, and the Francisella FnΔtrxA mutant also was found to have a marked T4P deficiency. Interestingly, a F. novicida mutant lacking pilT also showed increased hydrophobicity over FnWT. Collective evidence presented in this study suggests that Gram-negative bacterial thioredoxin mediates CSH through multiple mechanisms including disulfide-bond reduction and T4P modulation.

Transcriptomic insights on the virulence-controlling CsrA, BadR, RpoN, and RpoS regulatory networks in the Lyme disease spirochete.

Borrelia burgdorferi, the causative agent of Lyme disease, survives in nature through a cycle that alternates between ticks and vertebrates. To facilitate this defined lifestyle, B. burgdorferi has evolved a gene regulatory network that ensures transmission between those hosts, along with specific adaptations to niches within each host. Several regulatory proteins are known to be essential for the bacterium to complete these critical tasks, but interactions between regulators had not previously been investigated in detail, due to experimental uses of different strain backgrounds and growth conditions. To address that deficit in knowledge, the transcriptomic impacts of four critical regulatory proteins were examined in a uniform strain background. Pairs of mutants and their wild-type parent were grown simultaneously under a single, specific culture condition, permitting direct comparisons between the mutant strains. Transcriptomic analyses were strand-specific, and assayed both coding and noncoding RNAs. Intersection analyses identified regulatory overlaps between regulons, including transcripts involved in carbohydrate and polyamine metabolism. In addition, it was found that transcriptional units such as ospC and dbpBA, which were previously observed to be affected by alternative sigma factors, are transcribed by RNA polymerase using the housekeeping sigma factor, RpoD.

Microbial co-infection alters macrophage polarization, phagosomal escape, and microbial killing.

Macrophages are important innate immune cells that respond to microbial insults. In response to multi-bacterial infection, the macrophage activation state may change upon exposure to nascent mediators, which results in different bacterial killing mechanism(s). In this study, we utilized two respiratory bacterial pathogens, Mycobacterium bovis (Bacillus Calmette Guerin, BCG) and Francisella tularensis live vaccine strain (LVS) with different phagocyte evasion mechanisms, as model microbes to assess the influence of initial bacterial infection on the macrophage response to secondary infection. Non-activated (M0) macrophages or activated M2-polarized cells (J774 cells transfected with the mouse IL-4 gene) were first infected with BCG for 24-48 h, subsequently challenged with LVS, and the results of inhibition of LVS replication in the macrophages was assessed. BCG infection in M0 macrophages activated TLR2-MyD88 and Mincle-CARD9 signaling pathways, stimulating nitric oxide (NO) production and enhanced killing of LVS. BCG infection had little effect on LVS escape from phagosomes into the cytosol in M0 macrophages. In contrast, M2-polarized macrophages exhibited enhanced endosomal acidification, as well as inhibiting LVS replication. Pre-infection with BCG did not induce NO production and thus did not further reduce LVS replication. This study provides a model for studies of the complexity of macrophage activation in response to multi-bacterial infection.

Pathogenic Leptospires Modulate Protein Expression and Post-translational Modifications in Response to Mammalian Host Signals.

Pathogenic species of Leptospira cause leptospirosis, a bacterial zoonotic disease with a global distribution affecting over one million people annually. Reservoir hosts of leptospirosis, including rodents, dogs, and cattle, exhibit little to no signs of disease but shed large numbers of organisms in their urine. Transmission occurs when mucosal surfaces or abraded skin come into contact with infected urine or urine-contaminated water or soil. Whilst little is known about how Leptospira adapt to and persist within a reservoir host, in vitro studies suggest that leptospires alter their transcriptomic and proteomic profiles in response to environmental signals encountered during mammalian infection. We applied the dialysis membrane chamber (DMC) peritoneal implant model to compare the whole cell proteome of in vivo derived leptospires with that of leptospires cultivated in vitro at 30°C and 37°C by 2-dimensional difference in-gel electrophoresis (2-D DIGE). Of 1,735 protein spots aligned across 9 2-D DIGE gels, 202 protein spots were differentially expressed (p < 0.05, fold change >1.25 or < -1.25) across all three conditions. Differentially expressed proteins were excised for identification by mass spectrometry. Data are available via ProteomeXchange with identifier PXD006995. The greatest differences were detected when DMC-cultivated leptospires were compared with IV30- or IV37-cultivated leptospires, including the increased expression of multiple isoforms of Loa22, a known virulence factor. Unexpectedly, 20 protein isoforms of LipL32 and 7 isoforms of LipL41 were uniformly identified by DIGE as differentially expressed, suggesting that unique post-translational modifications (PTMs) are operative in response to mammalian host conditions. To test this hypothesis, a rat model of persistent renal colonization was used to isolate leptospires directly from the urine of experimentally infected rats. Comparison of urinary derived leptospires to IV30 leptospires by 2-D immunoblotting confirmed that modification of proteins with trimethyllysine and acetyllysine occurs to a different degree in response to mammalian host signals encountered during persistent renal colonization. These results provide novel insights into differential protein and PTMs present in response to mammalian host signals which can be used to further define the unique equilibrium that exists between pathogenic leptospires and their reservoir host of infection.

RNA-Seq of Borrelia burgdorferi in Multiple Phases of Growth Reveals Insights into the Dynamics of Gene Expression, Transcriptome Architecture, and Noncoding RNAs.

Borrelia burgdorferi, the agent of Lyme disease, differentially expresses numerous genes and proteins as it cycles between mammalian hosts and tick vectors. Insights on regulatory mechanisms have been provided by earlier studies that examined B. burgdorferi gene expression patterns during cultivation. However, prior studies examined bacteria at only a single time point of cultivation, providing only a snapshot of what is likely a dynamic transcriptional program driving B. burgdorferi adaptations to changes during culture growth phases. To address that concern, we performed RNA sequencing (RNA-Seq) analysis of B. burgdorferi cultures at early-exponential, mid-exponential, and early-stationary phases of growth. We found that expression of nearly 18% of annotated B. burgdorferi genes changed significantly during culture maturation. Moreover, genome-wide mapping of the B. burgdorferi transcriptome in different growth phases enabled insight on transcript boundaries, operon structures, and identified numerous putative non-coding RNAs. These RNA-Seq data are discussed and presented as a resource for the community of researchers seeking to better understand B. burgdorferi biology and pathogenesis.

Biological and physiological characterization of in vitro blood feeding in nymph and adult stages of Ornithodoros turicata (Acari: Argasidae).

Biological and physiological aspects of blood feeding in nymph and adult Ornithodoros turicata were investigated using an in vitro technique combined with electrophysiological recordings and respirometry. The duration of blood feeding through a Parafilm® membrane was similar (19.2-22.6 min) in both developmental stages. The mean (±SD) size of blood meal ingested by nymphs, females, and males was 44.2±17.9, 150.6±48.7, and 74.2±36.9 mg, respectively, representing a 2.5-, 2.8- and 3.0-fold increase from their respective unfed weights. Electrophysiological recordings of the pharyngeal pump during blood feeding revealed that ticks ingested blood at a rate of 6.1-6.4 suctions per second. Mean blood volume ingested per suction was 0.013 µl in females and 0.007 µl in both males and nymphs. Blood meal size (mg) correlated with unfed body weight (mg) (r(2)=0.50, p<0.05) and with blood volume ingested per suction (r(2)=0.71, p<0.05). Unfed ticks exhibited a circadian ventilation rhythm with discontinuous gas exchange pattern during the daytime and continuous pattern during nighttime. Mean standard metabolic rates (SMR, V̇(CO2)) in unfed nymphs, females and males of 1.4, 3.0 and 0.9 µl h(-1) increased to 2.0, 5.7 and 2.4 µl h(-1), respectively, after a blood meal. SMR correlated positively with blood meal size (r(2)=0.89, p<0.05). Mean coxal fluid weight excreted after a blood meal in nymphs, females, and males was 8.7, 20.0, and 7.7 mg, respectively, which represents 27.0%, 23.4% and 26.7% of their blood meal size. This study revealed biological and physiological characteristics of soft tick blood feeding and metabolism important to tick survival.

Evasion of IFN-γ signaling by Francisella novicida is dependent upon Francisella outer membrane protein C.

BACKGROUND: Francisella tularensis is a Gram-negative facultative intracellular bacterium and the causative agent of the lethal disease tularemia. An outer membrane protein (FTT0918) of F. tularensis subsp. tularensis has been identified as a virulence factor. We generated a F. novicida (F. tularensis subsp. novicida) FTN_0444 (homolog of FTT0918) fopC mutant to study the virulence-associated mechanism(s) of FTT0918. METHODS AND FINDINGS: The ΔfopC strain phenotype was characterized using immunological and biochemical assays. Attenuated virulence via the pulmonary route in wildtype C57BL/6 and BALB/c mice, as well as in knockout (KO) mice, including MHC I, MHC II, and µmT (B cell deficient), but not in IFN-γ or IFN-γR KO mice was observed. Primary bone marrow derived macrophages (BMDM) prepared from C57BL/6 mice treated with rIFN-γ exhibited greater inhibition of intracellular ΔfopC than wildtype U112 strain replication; whereas, IFN-γR KO macrophages showed no IFN-γ-dependent inhibition of ΔfopC replication. Moreover, phosphorylation of STAT1 was downregulated by the wildtype strain, but not the fopC mutant, in rIFN-γ treated macrophages. Addition of NG-monomethyl-L-arginine, an NOS inhibitor, led to an increase of ΔfopC replication to that seen in the BMDM unstimulated with rIFN-γ. Enzymatic screening of ΔfopC revealed aberrant acid phosphatase activity and localization. Furthermore, a greater abundance of different proteins in the culture supernatants of ΔfopC than that in the wildtype U112 strain was observed. CONCLUSIONS: F. novicida FopC protein facilitates evasion of IFN-γ-mediated immune defense(s) by down-regulation of STAT1 phosphorylation and nitric oxide production, thereby promoting virulence. Additionally, the FopC protein also may play a role in maintaining outer membrane stability (integrity) facilitating the activity and localization of acid phosphatases and other F. novicida cell components.

A bacterial two-hybrid system that utilizes Gateway cloning for rapid screening of protein-protein interactions.

Comprehensive clone sets representing the entire genome now exist for a large number of organisms. The Gateway entry clone sets are a particularly useful means to study gene function, given the ease of introduction into any Gateway-suitable destination vector. We have adapted a bacterial two-hybrid system for use with Gateway entry clone sets, such that potential interactions between proteins encoded within these clone sets can be determined by new destination vectors. We show that utilizing the Gateway clone sets for Francisella tularensis and Vibrio cholerae, known interactions between F. tularensis IglA and IglB and V. cholerae VipA and VipB could be confirmed with these destination vectors. Moreover, the introduction of unique tags into each vector allowed for visualization of the expressed hybrid proteins via Western immunoblot. This Gateway-suitable bacterial two-hybrid system provides a new tool for rapid screening of protein-protein interactions.

Vaccination with a defined Francisella tularensis subsp. novicida pathogenicity island mutant (DeltaiglB) induces protective immunity against homotypic and heterotypic challenge.

Francisella tularensis, an intracellular Gram-negative bacterium, is the causative agent of tularemia and a potential bioweapon. Currently, there is no licensed vaccine against this organism. We have characterized the efficacy of a defined F. tularensis subsp. novicida mutant (DeltaiglB) as a live attenuated vaccine against pneumonic tularemia. Replication of the iglB mutant (KKF235) in murine macrophages was significantly lower than the wild type novicida strain U112, and exhibited an LD(50) greater than 10(6)-fold (>10(7)CFU vs <10CFU) in an intranasal challenge model. Mice immunized with KKF235 intranasally or orally induced robust antigen-specific splenic IFN-gamma recall responses, as well as the production of systemic and mucosal antibodies. Intranasal vaccination with KKF235 protected mice from subsequent homotypic challenge with U112 as well as heterotypic challenge with F. tularensis subsp. holarctica (LVS). Moreover, protected animals also exhibited minimal pathological changes compared with mock-vaccinated and challenged animals. The protection conferred by KKF235 vaccination was shown to be highly dependent on endogenous IFN-gamma production. Most significantly, oral immunization with KKF235 protected mice from a highly lethal subsp. tularensis (SCHU S4) pulmonary challenge. Collectively, these results further suggest the feasibility of using defined pathogenicity island mutants as live vaccine candidates against pneumonic tularemia.