Loss of Fc gamma receptor and impaired phagocytosis of polymorphonuclear leukocytes in gingival crevicular fluid

Immunoglobulin G type II and III receptors (Fc gamma RII and Fc gamma RIII) are essential for polymorphonuclear leukocytic (PMNs) phagocytosis. Our previous study demonstrated a downregulation of Fc gamma RIII on PMNs in gingival crevicular fluid (GCF). To determine whether this receptor downregulation may contribute to the periodontal host defence borne by PMNs, we examined the correlation between Fc gamma RII and Fc gamma RIII expressions and the phagocytic capacity of GCF-PMNs. In order to verify at which level of cellular events the loss of Fc gamma R occurs, we quantified mRNA levels to assess a de novo synthesis of these receptors. GCF was collected from 21 patients with adult periodontitis by gingival crevicular washing. Autologous peripheral blood (PB) PMNs served as control. Surface expressions of Fc gamma Rs and phagocytic capacity via Fc gamma Rs were analysed by flow cytometry. The difference in Fc gamma R mRNA levels between GCF- and PB-PMNs was assessed by reverse transcription-polymerase chain reaction (RT-PCR). The amplified products were visualized by agarose gel electrophoresis and the endproduct yields were quantified by computerized image-analysis. Both Fc gamma RII and Fc gamma RIII expressions and phagocytic capacity on GCF-PMNs were significantly lower than those on PB-PMNs (p<0.001). The downregulation of Fc gamma Rs on GCF-PMNs significantly correlated with the phagocytic capacity (r = 0.66 for Fc gamma RIII, p < 0.01; r = 0.50 for Fc gamma RII, p < 0.05). The mRNA level of Fc gamma RIII of GCF-PMNs was significantly lower than that of PB-PMNs (p < 0.05). Thus, GCF-PMNs are characterized by the decreased surface expressions and mRNA levels of Fc gamma Rs, and the impaired phagocytosis.