Francisella tularensis is capable to modulate immunobiological activities of the host cells. We focused on the expression of ICAM-1 (CD54) on J774.2 mouse macrophage cell line infected by F. tularensis live vaccine strain (LVS) in vitro as a putative marker of subsequent elimination of infection. J774.2 cell line cells were infected by F. tularensis LVS strain (multiplicity of infection, 1:100). Cell cultures were stimulated either 3 h before infection or 3 h after infection by either lipopolysaccharide (LPS) or interferon γ (IFN-γ). The expression of ICAM-1 was determined by flow cytometry 6 h after infection. The intensity of ICAM-1 expression after 6 h of J774.2 macrophage cells infection by F. tularensis is very sensitive indicator of the effective macrophages stimulation resulting in the elimination of F. tularensis infection. The mean fluorescence intensity MFI = 49.8 is set-up by our experiments as a reliable threshold of the effective elimination of F. tularensis experimental infection with 83.3% sensitivity and 96.7% specificity, respectively. Simultaneous stimulation of J774.2 macrophage cells by LPS and IFN-γ was essential to elicit the elimination of F. tularensis infection. The ICAM-1 expression determined by flow cytometry can be considered to be highly sensitive and specific approach to predict elimination of F. tularensis infection by J774.2 macrophages.

Mutual interactions were investigated between intracellular parasitic bacterium Francisella tularensis (F.t.; highly virulent bacterium responsible for tularemia, replicating within the host macrophages) and murine macrophage-like cell line J774. Recombinant murine lymphokine INF-γ and/or LPS derived from E. coli were determined to stimulate in vitro antimicrobial activity of macrophage-like J774 cell line against the live vaccine strain (LVS) of F.t. through their ability to produce proinflammatory cytokines and chemokines. F.t. infection up-regulated IL-12 p40 production and down-regulated TNF-α production by stimulated macrophages; on the other hand, F.t. infection did not affect the production of IL-8, IL-6, MCP-5, and RANTES by stimulated macrophages. This showed that F.t. infection modulates the cytokine synthesis by J774 macrophage cell line.

Cellular and humoral components of innate immunity are able to identify danger signals both of the exogenous and endogenous origin. Exogenous danger signals are evolutionary conserved mosaics of danger patterns which are frequent in pathogenic microbes. Endogenous danger signals are raised during damage of self structures, by oxidative stress and/or by chemical modification of self molecules. Danger signals are identified by several families of molecules which are expressed on the surfaces of innate immunity cells. Among them the TLR receptors family which is associated with intracellular signaling pathway NF-kappaB is one of the most important. The inflammatory response is induced via activated NF-kappaB transcription factor.

The most important set of receptors for danger patterns are TLR receptors. Together ten different TLR receptors were identified so far. Majority of TLR receptors is expressed on the cell surface to identify extracellulary localized danger signals. Some TLR receptors are also expressed in the intracellular compartment to identify intracellular danger signals. Receptors for danger signals display individual differences delineated by genetic polymorphism. The individual immune reactivity is developed in the context of genetic predisposition and the exposition to variable environmental factors. The differences in an individual immune reactivity are probably responsible for individual susceptibility or resistance to the development of immunopathological reactivity, which is involved in the immunopathogenesis of atherosclerosis.

The in vitro and ex vivo murine models of infection with live vaccine strain of Francisella tularensis LVS were used for the study of early phases of bacteria-host cell interactions. The electron microscopic study revealed the ability of F. tularensis LVS to escape from the phagosomes. This ability is influenced by genetic background and immune status of the host. Subcellular fractionation of infected host cells confirmed the escape of tularemia microbes from phagosomes and their association with mitochondrial and endoplasmic reticulum proteins. Phenotypic analysis and analysis of cytokine profiles of infected J774 cell line documented the AA modulation of CD16/32, CD54, and CD86 expression and TNF-alpha, IL-6, IL-10, and IL-12 cytokine production.