Oral immunization of mice with the live vaccine strain (LVS) of Francisella tularensis protects mice against respiratory challenge with virulent type A F. tularensis

Abstract

Francisella tularensis is a gram-negative intracellular bacterium, and the causative agent of tularemia. The infection can be initiated by various routes and can manifest itself in several clinical forms with the disseminated typhoidal form initiated by inhalation being most fatal. The attenuated live vaccine strain (LVS), developed almost 50 years ago, remains the sole effective tularemia vaccine, which is still only available as an Investigational New Drug for at-risk individuals. This vaccine, when given by scarification, appears to provide solid protection against subsequent systemic infection with clinical strains of F. tularensis, but its efficacy against respiratory infection is less satisfactory. In this study, we evaluated the potential of oral immunization with LVS for eliciting protection against systemic and respiratory infection with virulent F. tularensis strains in a mouse model of tularemia. Oral LVS immunization was highly effective at protecting Balb/c mice against lethal systemic or respiratory challenges with type A and type B F. tularensis. Compared to shamimmunized mice, oral LVS-immunized mice showed significant reductions in burdens of virulent F. tularensis in the lung and spleen and milder tissue damage and inflammation in the liver. The immunization induced F. tularensis -specific antibody responses in the serum and bronchoalveolar lavage fluids, as well as antigen-specific splenocyte proliferation and IFN-γ and IL-2 production. The protective efficacy was related to the size of the immunizing dose but not the number of doses administered. Like other routes of LVS immunization in mice, the protective immunity induced by oral immunization was relatively short-lived. These results suggest that oral immunization should be explored further as an alternative vaccination strategy to combat tularemia.

Neutrophils Play an Important Role in Host Resistance to Respiratory Infection with Acinetobacter baumannii in Mice

“…For histopathological examination, the lung and spleen were fixed immediately in 10% neutral buffered formalin and processed by standard paraffin embedding methods (Department of Pathology and Laboratory Medicine, University of Ottawa, Ottawa, Ontario). Sections were cut 4 m thick, stained with hematoxylin-eosin, and examined by light microscopy (19).…”

“…For cytokine/chemokine mRNA expression analysis, the lung and spleen were dissected, immersed immediately in RNAlater (QIAGEN, Germantown, MD), and stored at Ϫ20 o C until extraction. Relative amounts of cytokine and chemokine mRNAs in the lung and spleen over the course of infection in the two groups of mice were estimated using a real-time PCR-based method essentially as described elsewhere (13,19). Briefly, total RNA was extracted from tissues, and cDNA was prepared, amplified, and quantified using primers and probes designed with the Primer3 program available at http://frodo.wi.mit.edu/cgi-bin/primer3/primer3_www.cgi.…”

“…Levels of cytokine and chemokine PCR products were normalized to ␤2 microglobulin, which was not differentially expressed over the course of infection in RB6-and rIgG-treated mice. Data are presented as the average of relative expression values compared to those in the corresponding tissues of mice killed immediately before infection (i.e., 0 h, uninfected) (19,21). The differences in ⌬C T between RB6-and rIgG-treated mice were compared by the Mann-Whitney U test, based on the method of Yuan et al (34).…”

“…Undiluted BAL samples and 1:2 diluted serum samples (50 l) were analyzed as specified by the manufacturer. The analysis was done in duplicate, and the cytokine/chemokine concentrations were calculated against the standards using Beadview software (version 1.03; Upstate) (19). Statistical analysis.…”

Susceptibility of selected murine and microtine species to infection by a wild strain of Francisella tularensis subsp. holoarctica

“…It was the objective of this study to provide data on differences in the susceptibility of Mus musculus (BALB/c mice), Apodemus flavicollis (yellow-necked mouse) and Microtus arvalis (common vole) to F. tularensis infection. While BALB/c mice represent the standard, as they are genetically defined experimental animals with much data available concerning their response to infection by F. tularensis Conlan et al, 2003;Green et al, 2005;KuoLee et al, 2007), yellow-necked mice and common voles have been reported to harbour F. tularensis with as high a prevalence as 3.9% during activation of tularemic foci in Central Europe (Gurycova et al, 2001;Vyrostekova et al, 2002). Though Dunaeva and Olsufyev (1958) consider these species highly susceptible to tularemia, the results of the present study demonstrate that there is a two-orders-of-magnitude difference in susceptibility to F. tularensis infection between BALB/c mice and common voles, with mice being more susceptible.…”