InactivatedFrancisella tularensisLive Vaccine Strain Protects against Respiratory Tularemia by Intranasal Vaccination in an Immunoglobulin A-Dependent Fashion

Abstract

Francisella tularensis is a gram-negative intracellular bacterium that is considered to be a potential category A biological weapon due to its extreme virulence. Although vaccination with the attenuated live vaccine strain (LVS) of F. tularensis can protect against lethal challenge, use of inactivated or subunit forms as vaccine candidates for induction of protective antibody responses has not been fully evaluated. In the present study, we examined whether immune protection in the lung could be stimulated by intranasal administration of inactivated LVS together with interleukin-12 (IL-12) as an adjuvant. LVS was inactivated by heat, paraformaldehyde treatment, or exposure to UV, and inactivation of the preparations was confirmed by assessing bacterial growth and the survival of mice after direct inoculation. We found that mucosal vaccination with inactivated LVS provided 90 to 100% protection in mice after lethal intranasal challenge with 10 4 CFU of LVS, and this protection was dependent on inclusion of exogenous IL-12 during vaccine administration. Survival of vaccinated mice after live bacterial challenge was correlated with reduced bacterial burden, decreased pulmonary inflammation, increased serum antibody titers, and lower levels of gamma interferon (IFN-␥), tumor necrosis factor alpha, and IL-6 in the lungs, livers, and spleens. Whereas NK cells were primarily responsible for the production of IFN-␥ in unvaccinated, challenged animals, vaccinated mice had increased levels of lung IFN-␥ ؉ CD4؉ T cells after challenge. Significantly, mice genetically deficient in immunoglobulin A (IgA) expression were unable to survive lethal challenge after vaccination. These results are the first results to demonstrate that IgA-mediated protection against lethal respiratory tularemia occurs after mucosal vaccination with inactivated F. tularensis LVS.

Monophosphoryl Lipid A Enhances Efficacy of a Francisella tularensis LVS-Catanionic Nanoparticle Subunit Vaccine against F. tularensis Schu S4 Challenge by Augmenting both Humoral and Cellular Immunity

“…tularensis replicates intracellularly, and thus the role of humoral immunity against this pathogen has been controversial; however, significant contributions of the humoral response in F. tularensis infection are supported by a growing body of literature (46)(47)(48)(49)(50)(51)(52). The fact that passive administration of LVS-VϩMPL immune sera fully protected mice against challenge with F. tularensis LVS (data not shown) and extended the mean time to death significantly in mice challenged with F. tularensis Schu S4 by the s.c. route, but not by the i.n.…”

Prophylactic and Therapeutic Use of Antibodies for Protection against Respiratory Infection with Francisella tularensis

“…Hence, adoptively transferred serum Abs have limited efficacy if given later than 48 h after infection. It is worth mentioning that in vaccinated mice, mucosal Abs such as IgA in addition to Ag-specific T cells may also contribute to overall protection (19). We are currently investigating the specific role of mucosal Abs in providing a first line defense against pulmonary tularemia.…”

IL-12 as an adjuvant for the enhancement of protective humoral immunity

“…These include infections induced with influenza virus [22], Streptococcus pneumoniae [23][24][25], Francisella tularensis [26] and Yersinia pestis [Kumar D, Metzger DW, Unpublished Data]. We and others have repeatedly found that intranasal treatment of mice with IL-12 leads to increases in expression of both Th1-and Th2-associated antibodies in the serum [9][10][11][12][13][14] as well as in the lung [22][23][24][25][26][27]. In a typical experiment, mice are inoculated intranasally with vaccine only or vaccine plus IL-12.…”