B-220. Differential Modulation of Phagocytic Cell Functions by the Burkholderia cepacia Complex: Burkholderia cenocepacia but not Burkholderia multivorans Disrupts Maturation and Induces Necrosis in Human Dendritic Cells

K. L. MacDonald, D. P. Speert;
Univ. of British Columbia, Vancouver, BC, CANADA.

Burkholderia cepacia complex (BCC) bacteria cause pulmonary infections which can evolve into fatal overwhelming septicemia in chronic granulomatous disease or cystic fibrosis (CF) patients. B. cenocepacia and B. multivorans cause the majority of BCC infections in CF patients, but they differ dramatically in apparent virulence: B. cenocepacia induces greater inflammation and toxicity than B. multivorans in a murine pulmonary infection model, and the former is associated with a much poorer prognosis in CF patients. Dendritic cells (DCs), one of the resident lung mononuclear phagocytes, are crucial cells linking innate and adaptive immunity and may serve as systemic vectors for this putative intracellular pathogen. We hypothesize that B. cenocepacia and B. multivorans modulate the normal functions of primary human monocyte-derived DCs. DCs were challenged with live B. multivorans or B. cenocepacia at a multiplicity of infection of 0.3:1. After 2 hours, 8 μg/ml of meropenem was added and the DCs were re-incubated up to 24 h. Effects of the bacteria on DC maturation were determined using flow cytometry. B. cenocepacia, but not B. multivorans, impaired DC maturation; DCs co-incubated for 24 hours with B. cenocepacia, but not B. multivorans, had reduced expression of co-stimulatory surface receptors when compared with BCC lipopolysaccharide-matured DCs. B. cenocepacia, but not B. multivorans, also induced significant necrosis in dendritic cells after 12-24 h, as determined by flow cytometry following annexin V and propidium iodide staining. DC necrosis only occurred after phagocytosis of live B. cenocepacia; DCs exposed to heat-killed bacteria, bacterial supernatant, or those pre-treated with cytochalasin D (to stop phagocytosis) then exposed to live bacteria remained viable. Cytokine enzyme linked absorbent assays revealed that B. multivorans and B. cenocepacia induced DCs to secrete similar amounts of IL-6, TNF-alpha, IL-10 and IL-12 after 24 hours. In conclusion, the ability of B. cenocepacia to interfere with DC maturation and induce necrosis may contribute to its pathogenicity in susceptible hosts, particularly those with CF.