Inhibition of Francisella tularensis phagocytosis using a novel anti-LPS scFv antibody fragment

Adva Mechaly,Eyal Epstein,Uri Elia,Ofer Cohen,Ron Alcalay,Hila Cohen,Ohad Mazor

doi:10.1038/s41598-019-47931-w

Adva Mechaly, Eyal Epstein + Show 5 more

Open Access

https://doi.org/10.1038/s41598-019-47931-w

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Journal: Scientific Reports	Publication Date: Aug 6, 2019
Citations: 13	License type: open-access

Affiliation: Israel Institute for Biological Research

Abstract

Francisella tularensis (Ft), the causative agent of lethal tularemia, is classified as a category A biological warfare threat agent. While Ft infection is treatable by antibiotics, many failed antibiotic treatments were reported, highlighting the need for effective new treatments. It has been demonstrated that binding of antibody-coated bacteria to the Fc receptor located on phagocytic cells is a key process needed for efficient protection against Ft. Yet, Ft utilizes the same receptor to enter the phagocytic cells in order to escape the immune system. To address the question whether an anti-Ft LPS antibody lacking the ability to bind the Fc receptor may inhibit the entry of Ft into host cells, a soluble scFv (TL1-scFv) was constructed from an anti Ft-LPS antibody (TL1) that was isolated from an immune single-chain (scFv) phage-display library. Bacterial uptake was assessed upon infection of macrophages with Ft live attenuated strain (LVS) in the presence of either TL1 or TL1-scFv. While incubation of LVS in the presence of TL1 greatly enhanced bacterial uptake, LVS uptake was significantly inhibited in the presence of TL1-scFv. These results prompt further experiments probing the therapeutic efficacy of TL1-scFv, alone or in combination with antibiotic treatment.

Highlights

Francisella tularensis (Ft), the causative agent of lethal tularemia, is a virulent Gram-negative, facultative intracellular bacterium
Several studies have shown that antibodies directed against the LPS of Ft can be used for the treatment of mice infected with Ft attenuated strain (LVS) and not for those infected with the virulent strain[9,10,11]
It was previously suggested that the failure of anti-Ft antibodies to provide efficient protection against the virulent strain, they can bind it very efficiently, is due to a complete shutdown of the inflammatory response needed for efficient antibody-mediated clearance of the bacteria[10]

Summary

LPS scFv antibody fragment

Adva Mechaly[1], Uri Elia[2], Ron Alcalay[2], Hila Cohen[2], Eyal Epstein[3], Ofer Cohen2 & Ohad Mazor[1]. While Ft utilizes several receptors, including Fc receptor (FcγR) to enter the cytosol and escape from the immune system[12,13,14,15], binding of antibody-coated bacteria to the same receptor is a key process needed for efficient protection against LVS9,16. This exact uptake mechanism is being investigated as a way to enhance the uptake of inactivated Ft in order to provoke efficient immune response and as a mean to create a platform for vaccination[17]. In this work we report the isolation of an anti-Ft LPS antibody that reduced bacterial uptake by cultured macrophages

Results and Discussion

Materials and Methods

Additional Information