Increased platelet activation in SLE patients and stimulation of MEG-01 cells. Platelet binding of annexin V (A), platelet-monocyte complexes (B), and expression of P-selectin (C) were measured by flow cytometry in healthy controls and SLE patients. The values are expressed as percentage of cells being positive compared with an antibody isotype control. The lines represent the median-value in each group. MEG-01 cells were cultured in the presence or absence of IFNα and type I IFN-regulated proteins were measured by flow cytometry (D). The results are expressed as the mean fluorescence index (MFI) ratio or as the cell concentration with 1 SD. The statistical significance is noted above each set of data with P values or signs where * indicates P < .05 and **, P < .01.