Opsonophagocytosis in infected urine: relation to pH and osmolality.

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.