[ODP-152] The identification of the immune evasion factors of Francisella tularensis
Francisella tularensis, a causative agent of tularemia is highly pathogenic gram-negative bacteria to human and animals. F. tularensis evade the host immune recognition and intracellularly proliferates. However, the detail mechanisms of the immune evasion are largely unknown. Here, we screened mutants that strongly induced host immune responses from transposon mutant library and identified factors responsible for the immune evasion. The human monocyte cell line U937 were infected with Francisella tularensis subsp. novicida (F. novicida) U112 transposon mutants and the concentration of tumor necrosis factor (TNF)-α in the supernatant were measured with ELISA. Among 3024 transposon mutants of F. novicida, 13 strains were isolated as strains that induced strongly host immune responses. Then, the transposon insertion sites were identified by sequence analysis. All the transposons were inserted on open reading frames of genomes and the genes responsible for immune evasion were identified. In these genes, we focused on pyrC gene related to pyrimidine metabolism. We investigated its effect on the immune evasion by constructed the gene deletion mutant (ΔpyrC). As the result, ΔpyrC mutant induced high levels of TNF-α compared with the wild-type strain. These results suggest that intact pyrC gene is required for the immune evasion of Francisella.