Rafik Hariri philanthropic and developmental contributions are countless. The most remarkable being the multifaceted support to educate more than 36,000 Lebanese university students within Lebanon, and beyond.
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PHAGOCYTOSIS OF LEGIONELLA PNEUMOPHILA
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Mahmoud A. HALABLAB
|
Univ. |
London |
Spec. |
Biosphere Science |
Deg. |
Year |
Pages |
|
Ph.D. |
1991 |
190 |
A mathematical model has been established to study the predation of Legionella pneumophila by human polymorphonuclear neutrophils (PMN) and amoebae. Although chemiluminescene (CL) increased with the increase in bacterial concentration even at very high concentration of 1:870 PMN/bacteria, subsequent increase in bacterial number (370 and 400) resulted in minor increase in CL. The majority of 'phagocytes were involved in phagocytosis after 90 min incubation with 1:90 PMN/bacteria as indicated by reduction of nitro‑blue tetrazolium (NBT). A fully automated image analysis system for enumerating and differentiating between triggered and un-triggered phagocytes was developed. Phagocytes involved in phagocytosis were estimated with an accuracy > 95% when compared to counting by eye.
The tetrazolium dye was further used in a novel technique to estimate the virulence of L. pneumophila. Legionella strains of differing virulence were incubated with a solution of NBT at a concentration of lmg ml-1 . Reduction of NBT to formazan occurred at a faster rate in the presence of virulent strains after 3h Incubation at 37ºC. The reaction was enhanced when Acanthamoeba Polyphaga or human neutrophils were added. Reduction appeared to be temperature dependent: at 37º C the reaction was faster than at 20º C. A highly activated oxidative metabolism was observed, using NBT reduction, in both neutrophils and amoebae challenged with the most virulent legionellas. Heat‑inactivated bacteria, on the hand, did not activate the respiratory burst in amoebae. Unlike phagocytes, amoebae failed to produce CL.
On microscopic examination, deposits of formazan around legionella cells inside amoebae similar to those deposited in human neutrophils were observed. Electron microscopy revealed electron‑dense particles surrounding virulent legionellae, which appeared to be associated with formazan formation. These deposits were roughly circular and varied in diameter (30‑60nm). More formazan deposition was associated with the virulent intracellular legionellae. When a virulent Legionella was employed, formazan deposits were embedded in the cell wall and occurred in only about 1 in 1000 cells.
