Protection against Legionnaire's Disease: Recombinant Flagellin A of Legionella pneumophila Can Induce Protective Immunity against Bacteremia in a BALB/c Murine Model

Abstract

To investigate the immunoprotective effects of the recombinant type A flagellin (FLA), the <i>fla</i>A gene of <i>Legionella pneumophila</i> serogroup 1 strain Paris was cloned into pET28a(+). Recombinant FLA (rFLA) was overexpressed in <i>E. coli</i> BL21 (DE3) and purified by Ni²⁺ exchange chromatography. Female BALB/c aged 6-8 weeks were immunized with 20 μg of rFLA. Nonimmunized mice along with mice inoculated with a sublethal dose of live <i>L. pneumophila</i> intravenously were considered as negative and positive controls, respectively. A significant serum antibody response was observed in female BALB/c mice immunized with rFLA. Production of IFN-&#x03B3; and IL-12, and TNF-α in the serum and the splenocyte cultures, and antigen-specific splenocyte proliferation suggested a strong innate and adaptive cell-mediated immunity response in rFLA-immunized mice. Intravenous lethal challenge with <i>L. pneumophila</i> serogroup 1 (strain Paris) showed that 60% of mice immunized with rFLA survived in a 10-day follow-up survey. These results show that rFLA from <i>L. pneumophila</i> can elicit strong innate and adaptive immune responses and suggest the possibility of a long-term immunity against lethal challenge with <i>L. pneumophila</i>.