MxA as biomarker for the activity of interferon-alpha in patients with chronic hepatitis: Measurement by flow cytometry

Background: The antiviral protein MxA is induced in leukocytes by type-I-interferons. An increased expression of MxA has been shown by means of PCR in patients with chronic hepatitis undergoing interferon-alpha therapy. Additionally, it has been demonstrated that the clinical response to interferon-alpha is correlated to the basal expression of MxA. Therefore, MxA has been proposed to serve as a marker for the bioactivity of interferon-alpha. We investigated the utility of flow cytometry (FACS) to measure the expression of MxA in different leukocyte cell types in patients with chronic hepatitis. Methods: The expression of MxA was determined in permeabilized whole blood samples by FACS analysis using a FITC-conjugated antibody (clone 383, An der Grub, Austria). The mean channel flourescence was determined after gating for neutrophils (PMN), monocytes (Mono) and lymphocytes (Lympho). Data are given as mean and standard deviation. Statistical analysis was done by t-test. Results: Blood samples were obtained from patients with chronic hepatitis B (CHB, n=7), chronic hepatitis C (CHC, n=10), CHC under treatment with interferon alpha (IFN, n=10), and healthy subjects (Contr., n=15). MxA expression was significantly increased in IFN (PMN: 15228, p<0.0001; Mono: 34873, p<0.0001; Lympho: 9220, p<0.0001) but not in CHB (PMN: 355, p=0.37; Mono: 38 5, p=0.53; Lympho: 243, p=0.33) or CHC (PMN: 5430, p=0.54; Mono: 378, p=0.66; Lympho: 222, p=0.16), as compared to Contr. (PMN: 4632, Mono: 3610, Lympho: 234). Conclusion: Interferon alpha-treatment results in a marked upregulation of MxA expression in patients with CHC. FACS analysis may serve as a convenient method in routine laboratory diagnostics for the monitoring of therapy in patients with chronic viral hepatitis.