Protection against Lethal Challenge by Legionella pneumophila in A/J Mice Following Immunization with Flagella

Abstract

This chapter talks about the role of the flagellum in the observed protection from legionella infection that was investigated by the authors. First, the minimal lethal dose (MLD) of two different strains of Legionella pneumophila was determined by infecting intraperitoneally (i.p.) female A/J mice, aged 4 to 6 weeks, with different doses of an L. pneumophila serogroup 6 strain of human origin (VIR+), or from the L. pneumophila serogroup 1 Corby strain. A flagellar preparation was performed from a 6-day culture of the flagellated VIR+ strain on buffered charcoal-yeast extract (BCYE; Oxoid, Italy) agar plates at 36№C, in humidified atmosphere and 2.5% CO2. Mice were observed for signs of illness and for survival for 15 days. In flagella-immunized mice, no mortality was observed, compared with 100% mortality of similarly challenged mice immunized with the sham-flagellar preparation or unimmunized control mice. Involvement of humoral immune responses in the protective effect due to flagellar immunization was investigated, also considering that flagella are present in most Legionella species and serogroups, and their composition is common in all of them.