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Factors affecting phagocytosis and killing by neutrophils in urine

Gargan, Robert A.; (1991) Factors affecting phagocytosis and killing by neutrophils in urine. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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A raised neutrophil count in infected urine is a well recognised occurrence. However, many aspects of phagocytosis and killing by PMN in urine are poorly understood. To investigate PMN function a simple, rapid and efficient isolation method using differential centrifugation was developed. Lysing PMN in water at pH 11 at 37° C made it possible to assess killing more accurately. The method of opsonisation proved to be a major determinant for intracellular killing. E.coli exposed to nutrients in serum or urine for 30 min, prior to being phagocytosed, developed resistance to phagolysosome killing. The same strains opsonised simultaneously on exposure to the PMN were rapidly killed. This acquired resistance correlated with the growth phase. Phagocytosis of E. coli and S.saprophyticus was efficient in urine over a wide pH range (6 to 8) and occurred between 200 to 700 mOsm. PMN bactericidal activity was more sensitive, being the first function to be lost, but was at least 90% of control values between pH 6.5 to 7 at 485 mOsm and still active at 200 mOsm. Bacterial metabolites in overnight cultures of E. coli in urine affected killing by PMN to a greater extent than phagocytosis. This was not due to endotoxin. PMN phagocytosis and killing could take place in urines passed by volunteers during the afternoon, but not in early morning specimens. This was due to adverse conditions (pH and osmolality) in the latter. Water loading or ingestion of 4 gm sodium citrate provided conditions in the urine that were more favourable to phagocytosis and killing by PMN. In 20 freshly voided infected urines, adverse conditions of pH and osmolality prevented the majority of PMN (60%) phagocytosing efficiently. This was despite opsonins (mainly IgG) being present in 17, and most PMN being viable and able to phagocytose when removed from the urines. Bacteria-associated factors were of minor importance. Thus, raising the pH and reducing the osmolality of infected urine should allow natural defence mechanisms to eliminate infecting organisms more efficiently.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Factors affecting phagocytosis and killing by neutrophils in urine
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Health and environmental sciences; Intracellular killing
URI: https://discovery.ucl.ac.uk/id/eprint/10120592
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