Clinical value of soluble IgG Fc receptor type III in plasma from patients with chronic idiopathic neutropenia

Abstract

Previous studies have shown that the plasma level of soluble IgG Fc receptor type III (sFcγRIII) is a measure of the total body neutrophil mass. The aim of this study was to determine whether the plasma level sFc-γRIII is associated with the risk of contracting bacterial infections in patients with neutropenia. We collected blood from 66 patients suffering from acquired idiopathic neutropenia, whose blood was sent to our laboratory for diagnostic evaluation of neutropenia (neutrophil count <1,500 cells/μL). Soluble FcγRIII levels were measured in plasma. Genotype distributions of FcγR polymorphisms were determined. Clinical data were obtained from the patient files. Patients were assessed as to whether or not they had suffered from a bacterial infection 3 months before to 3 months after a single sFcγRIII measurement. In addition, longitudinal data were obtained from 21 patients. Of the 66 neutropenic patients who were included, 15 had suffered from a bacterial infection in the period 3 months before to 3 months after sFc- γRIII measurement. The age and sex distribution was equal among the groups with and without infections, as were the genotype frequencies of neutrophil FcγR polymorphisms. Both neutrophil count and plasma level sFcγRIII were significantly lower in the patient group with infections, compared with the noninfected group (P = .03 and P < .0001, respectively). No infections were reported for patients who had plasma sFcγRIII levels above 100 arbitrary units (AU; normal value, 30 to 200). After matching each infected patient with two noninfected patients having the same neutrophil count, sFcγRIII plasma levels remained significantly lower in the group with infections (P = .0001). For the patients who were followed in time, no infections were reported when sFcγRIII levels were above 100 AU. In conclusion, our population of patients with chronic idiopathic neutropenia with plasma sFcγRIII levels above 100 AU did not show an increased risk of contracting bacterial infections.