CD64 (FcγRI) Expression on Neutrophil Granulocytes : A Diagnostic Marker of Acute Bacterial Infections

<b>Background. </b>Newborn infants, especially preterm infants, have an increased susceptibility to serious and overwhelming bacterial as well as fungal infections. Symptoms of septicaemia in especially the very preterm neonates are vague and unspecific. No really good biochemical parameter exists today that can confirm or exclude the existence of neonatal septicaemia. The access to such a test in neonates would be most valuable, not only to assure early institution of effective antibiotic therapy when needed, but also to avoid unnecessary use of antibiotics, thereby reducing the risk of further development of antimicrobial resistance. <b>Aim. </b>To investigate the possible use of the expression of the phagocyte receptor CD64 (FcγRI) on neutrophils for early diagnosis of bacterial infections with special reference to neonatal septicaemia. <b>Results. </b>Neutrophils from preterm and term newborn infants, older infants, children, and adults examined during the early phase of a bacterial infection showed a significantly higher expression of CD64 compared with non-infected controls (p&lt;0.001). Neutrophils from even extremely preterm infants expressed CD64 to the same extent as did neutrophils from children and adult patients. The expression of CD64 was not affected by the respiratory distress syndrome (RDS) or by such factors as premature rupture of the membranes, gestational age, steroid treatment before delivery, method of delivery, birth weight or postnatal age. Major surgery in adults (total hip replacement) did not affect the CD64 expression to an extent comparable to that found during bacterial infections. Indirectly CD64 was found to be at least equal to CRP for differentiation between Influenza A infection and bacterial infections in adults. <b>Conclusion.</b> CD64 was found to be a specific and reliable marker for early detection of bacterial infections in preterm and term newborn infants, as well as after surgery. For differentiation between bacterial and viral infections it is probably at least as effective as CRP