Previously, we generated a conditional mouse line, in which the IFN-b coding sequence is replaced by the reporter luciferase upon cell specific Cre expression [30] . Here we explored CD19cre, CD4cre and LysMcre mice to activate the reporter function in B cells, T cells, monocyte/macrophages and neutrophils. As reporter mice, we used mice that were heterozygous for the targeted mutation. This allowed IFN-b production from the functional wild type allele. To demonstrate the physiological relevance of IFN-b produced by the cell types mentioned above, we included mice homozygous for the conditional deletion and compared them with mice in which IFN-b was deleted in germ line. Overview of transgenic mice used in this paper is presented in Figure S1 .