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Opsonophagocytosis in infected urine: relation to pH and osmolality
R A Gargan1, J M Hamilton-Miller
1Department of Medical Microbiology, Royal Free Hospital and School of Medicine, London, United Kingdom.
Abstract:
Polymorphonuclear neutrophils (PMN) in freshly voided urines from 20 symptomatic bacteriuric patients were examined. Although the PMN were viable (median 85%), in only 2 cases could phagocytosis of the infecting organisms be demonstrated, even after the addition of serum opsonins. Polymorphonuclear neutrophils from urines of 12 patients were also unable to phagocytose added opsonized Staphylococcus aureus. These urines were found to be of pH < 6.0 and/or osmolality > 700, or < 180 mOsm. However, the phagocytic function of these PMN was restored when transferred to Hanks balanced salt solution (HBSS). By contrast, most PMN in urines of suitable pH (> or = 6.0) and osmolality (between 200 to 700 mOsm.) phagocytosed the opsonized S. aureus. When bacteria cultured from the infected urine were incubated in the same urine and then transferred to HBSS, in 17 of 19 cases opsonization occurred and the organisms were phagocytosed when PMN, isolated from blood, were added. IgG appeared to be the prime opsonin in the urines, and heat-stable opsonins for S. aureus were also present. It is concluded that lack of opsonization is not a major cause of the absence of phagocytosis by urinary PMN. Low pH and adverse osmolality are largely responsible, correction of which may restore PMN function in vivo.
Insights
Urinary polymorphonuclear neutrophils (PMN) struggle to phagocytose bacteria due to urine
Area of Science:
- Urology
- Immunology
- Microbiology
Background:
- Symptomatic bacteriuria involves polymorphonuclear neutrophils (PMN) in urine.
- Impaired PMN phagocytosis is observed in urinary tract infections.
Purpose of the Study:
- To investigate the phagocytic capacity of urinary PMN.
- To identify factors affecting PMN phagocytosis in urine.
Main Methods:
- Examined PMN viability and phagocytosis in urine from bacteriuric patients.
- Tested PMN phagocytosis of Staphylococcus aureus with and without serum opsonins.
- Assessed the impact of urine pH and osmolality on PMN function.
Main Results:
- Urinary PMN showed limited phagocytosis, even with added opsonins.
- Low urine pH (<6.0) and extreme osmolality (<180 or >700 mOsm) inhibited PMN phagocytosis.
- PMN phagocytic function was restored in Hanks balanced salt solution (HBSS).
- Opsonization and phagocytosis occurred when bacteria were incubated in urine and then transferred to HBSS with blood-derived PMN.
Conclusions:
- Impaired phagocytosis by urinary PMN is primarily due to adverse urine pH and osmolality, not lack of opsonization.
- Correcting urine pH and osmolality may restore PMN phagocytic function in vivo.