IL-8 released from human lung epithelial cells induced by cystic fibrosis pathogens Burkholderia cepacia complex affects the growth and intracellular survival of bacteria

Abstract

Burkholderia cepacia complex (Bcc) is a group of Gram-negative pulmonary pathogens associated with life-threatening infections in patients with cystic fibrosis (CF). The airway epithelium plays a crucial role in the initiation and modulation of inflammatory responses to these pathogens. Interleukin (IL)-8 released from epithelial cells is a potent chemoattractant for neutrophils. The aims of this study were to compare the IL-8 response to Bcc infection in different epithelial cell types and to investigate the impact of IL-8 on Bcc growth and intracellular survival. To compare epithelial cell IL-8 responses, 4 human epithelial cell lines were used in the study; A549 cells, an alveolar epithelial cell line, Calu-3 cells, a sub-bronchial epithelial cell line, 16HBE14o- cells, and CFBE41o- cells, which are CFTR-positive and CFTR-negative bronchial epithelial cell lines, respectively. Two B. multivorans and 2 B. cenocepacia strains all induced a significant IL-8 response by 12 h and further increased in all cell lines at 24 h. Furthermore, the levels of IL-8 from Calu-3 and A549 cells were approximately 3 times that of 16HBE14o- or CFBE41o- cells. In 2 of the cell lines examined (16HBE14o- and CFBE41o-), B. cenocepacia LMG 16656 (J2315), an epidemic strain, induced greater levels of IL-8 (P<0.01) compared to other Bcc strains tested. The CFTR-positive and -negative cell lines secreted similar levels of IL-8 indicating a CFTR-independent induction of IL-8. However, the CFTR-negative cells did secrete constitutive levels of IL-8 greater than that of CFTR-positive cells. An investigation of the effect of IL-8 on Bcc extracellular and intracellular growth found that at low concentrations (<10 ng/ml) of recombinant human (rh) IL-8, the growth of B. cenocepacia LMG 16656 and B. multivorans LMG 13010 was enhanced, whereas at higher concentrations (10 ng/ml), growth of both strains was significantly reduced. Growth of both non-CF Bcc strains remained unchanged in the presence of rhIL-8. In contrast to extracellular growth, higher concentrations (10ng/ml) of rhIL-8 enhance the intracellular growth and survival of both LMG 16656 and LMG 13010 in 16HBE14o- and CFBE41o- cell lines. Although LMG 13010 uptake by epithelial cells was higher than LMG 16656 (P<0.01), the intracellular growth of LMG 16656 is greater than LMG 13010 (P<0.05). These studies demonstrated that the type of epithelial cells encountered by Bcc strains determines the extent of the IL-8 responses triggered and that this cytokine in addition to its well-established proinflammatory properties can enhance both the extracellular and intracellular growth of Bcc strains.