The type I Fc receptor for immunoglobulin G (FcγRl, CD64) is a membrane glycoprotein expressed by polymorphonuclear leukocytes (PMNs). While constitutive expression of FcγRl is minimal, rapid upregulation under the influence of inflammatory mediators (IFNg, G-CSF, GM-CSF) has been demonstrated. Early studies suggest that increased expression of FcγRl may occur during states of acute infection. To better characterize the pattem of expression of FcγRl during the PMN response to infection, we used flow cytometry to quantitate FcγRl expression in a primate model of sepsis. Under a separate protocol at the Southwest Foundation for Biomedical Research, eight healthy adult male baboons (Papio cynocephalus) received intravenous infusions of Escherichia coli. Ventilator, fluid, and pressor support were provided as needed. Blood samples for flow cytometry and complete blood count were collected pre-infusion (0 hours) and at 6, 12, 18, 24, 48, and 72 hours post-infusion. All eight animals survived to 6 hours. Two animals survived to 72 hours; the remaining six died from septic shock prior to the end of the experiment. Flow cytometry data from two animals could not be used due to lab error. Mean FcγRl expression at baseline was 7.2 ± 4.7 percent (N = 6). Six hours after starting the E coli infusion, the mean expression was 26.1 ± 8.99 percent(N = 6, p =.006 vs. 0 hrs). Mean FcγRl expression increased at each time interval in the surviving animals, to a maximum of 96.2 ± 2.0 percent(N= 2). Regression analysis demonstrated that FcγRl increased linearly with the log of time (r2 =.89, p = <.0001). Total white blood cell count, absolute neutrophil count, and immature to total neutrophil ratio did not have a linear relationship with time, but rather tended to follow a biphasic pattern. When compared to traditional clinical markers for infection, FcγRl expression was unique in its rapid and consistent response. Further studies are needed to determine the clinical usefulness of this assay.Figure

figure 1