Differential expression of Fc receptors for IgG by monocytes and granulocytes from neonates and adults

The immature neonatal immune system is thought to result in increased risk of infection. Receptors for the Pc moiety of IgG (Fc gamma R) are important in antibody-mediated clearance of microbes by granulocytes and monocytes/macrophages. As an approach to understanding their role in neonatal life, we have compared the constitutive expression of the three Fc receptors-Fc gamma RI (CD64), Fc gamma RII (CD32) and Fc gamma RIII (CD16)-by neonatal and adult blood monocytes and granulocytes using quantitative immunofluorescence by flow cytometry. Our results confirm that there is a small subpopulation of Fc gamma RIII-positive monocytes in adult blood, and furthermore show that this is absent or at a low percentage in cord blood samples. However, the main population of cord blood monocytes expresses low, but significantly higher levels of Fc gamma RIII than adult monocytes. No differences were seen in the quantitative expression of Fc gamma RI and Fc gamma RII. Neonatal granulocytes expressed significantly higher levels of both Fc gamma RI and Fc gamma RII but significantly lower levels of Fc gamma RIII. The data are discussed in terms of the possible role of cytokines and susceptibility to infection.