A 3D Organotypic Human Bronchial Model Reveals Persistent Infection and Modulated Inflammatory Response when Exposed to Brucella abortus

Abstract

Brucella infection is frequently acquired by inhalation, but the pathogen disseminates systemicallyfrom the lungs. However, little is known about the interaction of Brucella spp. withthe airways. Using a 3D air-exposed organotypic human bronchial tissue model (polarized16HBE14o- bronchial epithelial cells grown over a collagen matrix containing MRC-5 lungfibroblasts), we analyzed Brucella abortus replication, translocation and cytokine responsesover prolonged post-infection times. Apically inoculated B. abortus invaded, replicated andpersisted during the whole follow-up (16 days) within the bronchial tissue without inducingcytotoxicity. Viable bacteria were also detected in the conditioned medium (CM) sinceday five post-infection, indicating release from the basolateral side. In parallel experiments,no invasion or bacterial release was detected for Escherichia coli. The levels of IL-6, IL-8 andMCP-1 were increased in CM from Brucella-infected 3D cultures and in monocultures ofpolarized bronchial epithelial cells or lung fibroblasts. Collagenase/gelatinase activity wasincreased in 3D cultures and MRC-5 monocultures. Infection transference from bronchialcells to lung fibroblasts was documented using monocultures. An immune cross-talk wasdetected, as cytokine levels were increased in fibroblasts stimulated with bronchial CM,and vice versa. These results suggest that the bronchial mucosa can sustain B. abortuspersistence, replication and dissemination, and that it induces a proinflammatory responseto which both epithelial cells and fibroblasts contribute.