Burkholderia infection stimulates a robust type I IFN response in macrophages, protecting them from intracellular replication.

A) iBMDMs or B) differentiated THP-1 cells were pre-treated with recombinant IFNβ or IFNγ for the indicated times, after which media was replaced and cells were infected with Bc (MOI = 1) for 22 h. Cells were lysed and lysates were cultured for 24 h before enumerating colonies; n = 5 per condition, representative of 3 independent experiments. C, D) WT and Ifnar1^-/- macrophages were infected with C) Bc (MOI = 1) or D) Burkholderia thailandensis (MOI = 1) for 22h before cells were lysed. Lysates were then cultured and bacterial colonies were enumerated after 24 h of growth. E, F) WT and Ifnar1^-/- iBMDMs were infected with live dsRed+ Bc (MOI = 1) and fixed in 2% PFA after 22 h. Bacterial load was analyzed using E) flow cytometry or F) high-content imaging based on dsRed fluorescence. G) WT and Ifnar1^-/- iBMDMs were infected with wt Bc (MOI = 1) for the indicated times before being lysed. Lysates were plated, as in 2C, and bacterial colonies were counted after 24 h of culture on blood agar plates. All Bc replication experiments above had n ≥ 5 and are representative of ≥ 3 experiments. * = p≤0.05, ** = p≤0.01, and **** = p≤0.0001 by Mann-Whitney U test.