Phagocyte function in uremia

Neutrophil dysfunction and infection risk in end-stage renal disease

Infections are still a major cause of morbidity and mortality in end-stage renal disease (ESRD) patients. The susceptibility of ESRD patients to infections is typically ascribed to the immunodeficient state associated with uremia. A central role in the host defense against bacterial infections is played by phagocytic polymorphonuclear white blood cells, which are characterized by the capacity to ingest and subsequently destroy bacteria. Disorders in polymorphonuclear cell function are exacerbated by the dialysis procedure and numerous factors including uremic toxins, iron overload, anemia of renal disease, and dialyzer bioincompatibility. It is concluded that the phagocytic defect observed in ESRD is multifactorial, and each factor should be managed individually with specific therapeutic approaches.

Defective regulation of iron transporters leading to iron excess in the polymorphonuclear leukocytes of patients on maintenance hemodialysis

BACKGROUND

Although hemodialysis (HD) patients are suspected of having defectively regulated iron metabolism, intracellular iron status has never been investigated thoroughly. To clarify the iron metabolism of HD patients, proteins involved in iron import (transferrin receptor [TfR]), as well as export (ferroportin 1), were investigated in polymorphonuclear leukocytes (PMNLs). Relations between iron status and several PMNL functions also were tested.

METHODS

Seventeen HD patients and 17 controls were recruited. Relative quantitative polymerase chain reaction was used to measure ferroportin 1 and TfR messenger RNA (mRNA), and ferroportin 1 and TfR expression were semiquantified by means of Western blot analysis or immunohistochemistry. PMNL functions also were examined.

RESULTS

Serum iron levels were significantly lower in HD patients than controls, and serum ferritin levels, as well as PMNL ferritin and iron content, were elevated in HD patients. Ferroportin 1 mRNA levels were substantially lower in PMNLs from HD patients, whereas TfR mRNA levels were higher. Western blot analysis and immunohistochemistry confirmed that expression of the corresponding proteins paralleled those of the mRNAs. PMNL phagocytic and bactericidal activity did not differ between HD patients and controls. Chemotactic peptide f-Met-Leu-Phe-stimulated degranulation activity of lactoferrin (Lf) was decreased significantly in HD patients, whereas those of myeloperoxidase and elastase were accelerated. Lf release correlated negatively with intracellular ferritin level.

CONCLUSION

We show for the first time that increased iron levels in PMNLs of HD patients were associated with downregulation of ferroportin 1 and upregulation of TfR, which might be linked to hypercytokinemia.

Neutrophil beta(2)-microglobulin and lactoferrin content in renal failure patients

Multiple dysfunctions of polymorphonuclear leukocytes (PMNLs) contribute significantly to the increased morbidity and mortality among patients with end-stage renal disease. In the present study, we measured the PMNL content of beta(2)-microglobulin (beta(2)m) and lactoferrin in different states of renal insufficiency and after kidney transplantation. PMNLs were lysed ultrasonically and, after centrifugation, both proteins were assayed in the supernatant by enzyme-linked immunosorbent assay technique. Despite marked differences in plasma beta(2)m levels, no significant difference in PMNL content of beta(2)m and lactoferrin could be shown among the groups analyzed. There was also no correlation between plasma beta(2)m level and PMNL beta(2)m content. In control subjects, as well as in renal allograft recipients with a well-functioning graft, PMNL beta(2)m level correlated positively with PMNL lactoferrin level (pooled data, r = 0.55; P < 0.001; n = 55). Both proteins are considered to colocalize in peroxidase-negative PMNL granules. However, no correlation was found in the azotemic and uremic patient groups. Standard immunofluorescence staining of control PMNLs showed a cytoplasmic granular distribution of both granule proteins. However, in PMNLs of uremic patients, lactoferrin shifted to a perinuclear localization. PMNLs obtained from uremic individuals failed to elicit an increase in lactoferrin release after stimulation with the chemotactic peptide f-Met-Leu-Phe compared with PMNLs obtained from healthy volunteers. These data indicate abnormalities in uremic patients of PMNL granule lactoferrin content and release that are reversible after successful renal transplantation.