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P186. Granulocyte activation as measured by CD64 expression on PMNs reflects inflammatory load in inflammatory bowel disease

A. Eser1, C. Primas2, P. Papay3, C. Lichtenberger4, A. Mikulits1, S. Angelberger5, G. Novacek4, H. Vogelsang6, W. Tillinger1, W. Reinisch7

1Medical University of Vienna, Gastroenterology and Hepatology, Vienna, Austria; 2Medical University of Vienna, Div. Of Gastroenterology and Hepatology, Vienna, Austria; 3Medical University of Vienna, Department of Internal Medicine III, Division of Gastroenterology, Vienna, Austria; 4Medical University of Vienna, Vienna, Austria; 5Medical University of Vienna, Internal Med. III, Div. Of Gastroenterology & Hepatology, Vienna, Austria; 6AKH Wien, Gastroenterology&Hepatology, Vienna, Austria; 7AKH Wien, Department of Internal Medicine IV, Vienna, Austria

Background: CD64, the high affinity immunoglobulin Fc gamma receptor I (FcgammaRI) is constitutively expressed on monocytes but up regulated during acute phase reaction on polymorphonuclear neutrophils (PMN). Measured on PMNs, CD64 expression is a sensitive biomarker for bacterial infection. Chronic Inflammatory bowel diseases (IBD) such as Crohn's disease (CD) and ulcerative colitis (UC) are considered to be mediated at least in part by the interaction of gut bacteria with the innate immune system. C‑reactive-protein (CRP) and orosomucoid (alpha1-GP) have been shown to reflect disease activity in IBD. These were compared to granulocyte activation, as measured by CD64 expression on PMNs.

Methods: We included 70 patients with histologically established diagnosis of Crohn's disease (CD, n = 39) and ulcerative colitis (UC, n = 31) as well as 7 healthy donors (HD). 27 of CD and 20 of UC patients were classified as active by the use of the Harvey–Bradshaw Index for Crohn's disease and partial Mayo score for ulcerative colitis. Bacterial infection was ruled out by standard culture methods. PMNs were stained for CD64/CD45 (QuantiBRITE, BD Biosciences) in full blood and measured by flow cytometry on FACS Calibur (BD Biosciences) according to manufacturer's description.

Results: CD64 is found on PMNs of CD and UC patients and healthy donors at a median count of 1954, 958 and 429 molecules/cell. A significant correlation of CD64 with CRP (tau = 0.63, p < 0.001) and alpha1-GP (tau = 0.62, p < 0.001) in CD and in UC (tau = 0.44, p = 0.027 for CRP and tau = 0.382 p = 0.003) was detected. In active CD (n = 27), a median CD64 count of 2911 m/cell as compared to inactive disease (n = 12, 707m/cell) was found (p < 0.000). In UC, CD64 was detected at a median density of 1824 and 650 m/cell in active (n = 20) and inactive disease (n = 11), respectively (p = 0.025). Receiver operating curve for the distinction of active and inactive disease yielded a sensitivity and specificity of 93% and 77% for CD64 at a cut off of 1015 m/cell for CD and of 75% and 64% at a cut off of 671 m/cell for UC.

Conclusions: CD64 expression on PMNs is well correlated with CRP and alpha1-GP established markers of inflammation for IBD. Quantitative assessment of CD64 on PMNs by flow cytometry distinguishes active from in active disease in IBD with excellent sensitivity in CD and with moderate sensitivity in UC. Granulocyte activation by CD64 is thereby implicated as useful biomarker for disease monitoring in Crohn's disease.