Resident CD11c+ lung cells are impaired by anthrax toxins after spore infection

Bacillus anthracis secretes 2 toxins: lethal toxin (LT) and edema toxin (ET). We investigated their role in the physiopathologic mechanisms of inhalational anthrax by evaluating murine lung dendritic cell (LDC) functions after infection with B. anthracis strains secreting LT, ET, or both or with a nontoxinogenic strain. Three lung cell populations gated on CD11c/CD11b expression were obtained after lung digestion: (1) CD11c high /CD11b low (alveolar macrophages), (2) CD11c intermediate (int) /CD11b int (LDCs), and (3) CD11c low /CD11b high (interstitial macrophages or monocytes). After infection with LT-secreting strains, a decrease in costimulatory molecule expression on LDCs was observed. All CD11c + cells infected with a nontoxinogenic strain secreted tumor necrosis factor (TNF)–a, interleukin (IL)–10, and IL-6. LT-secreting strains inhibited overall cytokine secretion, whereas the ET-secreting strain inhibited only TNF-a secretion and increased IL-6 secretion. Similar results were obtained after preincubation with purified toxins. Our results suggest that anthrax toxins secreted during infection impair LDC function and suppress the innate immune response.