A Novel Modification of a Flow Cytometric Assay of Phosphorylated STAT1 in Whole Blood Monocytes for Immunomonitoring of Patients on IFNα Regimen

We explored whether episodes stimulating leucocytes in vivo could be tracked from whole blood samples by monitoring activation of STAT1 by flow cytometry. The method was tested in hepatitis C patients (n = 9) that were on interferon (IFN)alpha regimen. CD14+ monocytes responded strongly to IFNalpha/gamma being sensitive indicators for recent immune activation. At 45 min after s.c. IFNalpha 91% of monocytes were phosphorylated STAT1+. The frequency of responding cells decreased to a base level within 6 h. Monocytes, however, had a long-term deficient phosphorylated STAT1 response to IFNalphain vitro that in patients on standard IFNalpha regimen lasted for 48 h. In patients on pegylated IFNalpha the phosphorylated STAT1 response was completely absent. We conclude that whole blood analysis of STAT1 activation by flow cytometry is applicable to monitor immune cells in patient material.