The levels IFNγ, a cytokine that is known to be protective during several bacterial infections, including tularemia [29] [30] [31] [32] [33], were reduced in Il-18-/- mice, a finding consistent with the established function of IL-18 as an IFNγ-inducing cytokine [29], but were significantly increased in BALF or sera of Il-1r1-/- mice, a likely reflection of the high level of IL-18 in these mice. This evidence concerns the gene IL1R1 and tularemia.