Intranasal Interleukin-12 Treatment for Protection against Respiratory Infection with theFrancisella tularensisLive Vaccine Strain

Abstract

Francisella tularensis is a gram-negative intracellular bacterium that can induce lethal respiratory infection in humans and rodents. However, little is known about the role of innate or adaptive immunity in protection from respiratory tularemia. In the present study, the role of interleukin-12 (IL-12) in inducing protective immunity in the lungs against intranasal infection of mice with the live vaccine strain (LVS) of F. tularensis was investigated. It was found that gamma interferon (IFN-␥) and IL-12 were strictly required for protection, since mice deficient in IFN-␥, IL-12 p35, or IL-12 p40 all succumbed to LVS doses that were sublethal for wild-type mice. Furthermore, exogenous IL-12 treatment 24 h before intranasal infection with a lethal dose of LVS (10,000 CFU) significantly decreased bacterial loads in the lungs, livers, and spleens of wild-type BALB/c and C57BL/6 mice and allowed the animals to survive infection; such protection was not observed in IFN-␥-deficient mice. The resistance induced by IL-12 to LVS infection was still observed in NK cell-deficient beige mice but not in CD8 ؊/؊ mice. These results demonstrate that exogenous IL-12 delivered intranasally can prevent respiratory tularemia through a mechanism that is at least partially dependent upon the expression of IFN-␥ and CD8 T cells.

Francisella tularensis LVS grown in macrophages has reduced ability to stimulate the secretion of inflammatory cytokines by macrophages in vitro

“…Consistent with this hypothesis, it has been shown that administration of neutralizing antibodies against tumor necrosis factor-α (TNF-α) or interferon-γ (IFN-γ) results in early death or a decrease in LD50 of mice infected with F. tularensis (8,14,17,19,24). IFN-γ null mice are also more susceptible to F. tularensis infection than their wild type counterparts (11). Treatment of macrophages with IFN-γ allows these cells to limit the growth of F. tularensis (1,2,15,22).…”

“…Survival studies were carried out using intranasal infection of mice as described by Duckett et al (11). Briefly, mice were anesthetized with ketamine and xylazine and were infected with FtB or FtMac in 40 ul of Ringer's solution containing 5,000 CFU.…”

Francisella tularensis:Taxonomy, Genetics, and Immunopathogenesis of a Potential Agent of Biowarfare

“…novicida (9,43,45,46,51,59,79,81). IL-12 is a potent stimulus for production of IFN-γ, which in turn induces nitric oxidase synthase (iNOS) and synthesis of NO by macrophages (11,38,51,62,63).…”

Phosphatidylinositol 3-Kinase Activation Attenuates the TLR2-Mediated Macrophage Proinflammatory Cytokine Response toFrancisella tularensisLive Vaccine Strain

“…Recent studies suggest that an inadequate innate immune response to infection with F. tularensis likely contributes to its extreme virulence in humans and mice. Indeed, proinflammatory cytokines such as TNF, IL-12, and IFN-g appear crucial for effective immunity to and survival of F. tularensis infection (3)(4)(5)(6), yet infection itself appears to attenuate or delay the expression of these critical cytokines (7)(8)(9)(10). The mechanism(s) by which F. tularensis infection delays or impairs the proinflammatory response remain unknown.…”