Flagellin-Deficient Legionella Mutants Evade Caspase-1- and Naip5-Mediated Macrophage Immunity
Figure 3
Rapid Lysis of Macrophages in Response to Flagellin-Expressing Legionella
In all experiments shown, bacteria were added at an MOI of 2, and were spun onto the macrophages at 400 g for 10 min. Cells were assayed 4 h after infection. LP02 is the wild-type strain and is isogenic with the mutants utilized in these experiments.
(A) Release of the intracellular enzyme LDH by B6 and MyD88−/− macrophages with indicated Legionella strains, including four mutants with transposon insertions in flaA. One hundred percent release is set as the amount of LDH released by detergent-treated macrophages (minus spontaneous release).
(B) LDH release by B6, B6.A-Chr13, and B6 caspase-1-deficient macrophages infected with the indicated Legionella strains. FlaAΔ56 is an LP02-derived strain that contains an EMS-induced point mutation in flaA, resulting in a truncation of the last 56 amino acids of FlaA.
(C) Cell death of macrophages was assessed by degree of failure to take up neutral red in a 4-h assay. At least 100 macrophages were counted for each condition; one representative experiment of two is shown.
(D) Cell death was quantified by assessing permeability to ethidium bromide-2 homodimer. At least 400 macrophages were counted for each condition; one representative experiment of two is shown.
