CONICET | Buscador de Institutos y Recursos Humanos

Although Brucella frequently infects humans through inhalation, its interaction with pulmonary cells has been overlooked. CCL20 is a potent chemoattractant for immature dendritic cells and T cells. Antimicrobial activities for CCL20 have been recently reported. We evaluated the antimicrobial activity of CCL20 against Brucella abortus, and whether this pathogen induces the secretion of CCL20 in human bronchial (Calu-6) and alveolar (A549) epithelial cells and macrophages (PMA-treated THP-1 cells). CCL20 killed B. abortus with a lethal dose (LD50, achieving 50% reduction of CFU) of 50 ug/ml. Cells were infected for 2 hours at multiplicities of infection (MOI) of 50 to 500 bacteria/cell (epithelial cells) or 10 to 100 bacteria/cell (macrophages). At 24 and 48 h post-infection CCL20 was measured by ELISA in culture supernatants. Infection significantly increased the production of CCL20 in macrophages and bronchial epithelial cells in a MOI-dependent manner (p<0.05). Both cell types also secreted CCL20 in response to heat-killed B. abortus and to PAMPs used for comparison (flagellin, Pam3Cys and E. coli LPS). In contrast, B. abortus LPS did not induce CCL20 secretion. Whereas the infection of A549 alveolar cells induced a slight, non-significant increase of CCL20 (p>0.05), the stimulation of these cells with conditioned medium from B. abortus-infected macrophages (CoIM) induced CCL20 secretion in a dose dependent manner (p<0.05). Neutralization assays with the antagonist of IL-1β receptor (IL-1Ra) showed that IL-1β present in CoIM is mostly responsible for this induction, whereas an anti-TNFα antibody had no effect. This study shows that bronchial epithelial cells and macrophages secrete CCL20 upon infection with B. abortus or stimulation with its antigens, while alveolar epithelial cells do so after stimulation by factors secreted by infected macrophages. CCL20 has antimicrobial activity against B. abortus.