AbstractThe tripartite motif (TRIM) proteins are important in a variety of cellular functions additional to anti‐viral activity. We systematically analysed mRNA expression of representative TRIM molecules in mouse macrophages, myeloid and plasmacytoid dendritic cells, and a selection of CD4+ T cell subsets. We defined four clusters of TRIM genes based on their selective expression in these cells. The first group of TRIM genes was preferentially expressed in CD4+ T cells and contained the COS‐FN3 motif previously shown to be involved in protein interactions. Additional TRIM genes were identified that showed up‐regulation in macrophages and dendritic cells upon influenza virus infection in a type I IFN‐dependent manner, suggesting that they have anti‐viral activity. In support of this notion, a subset of these TRIM molecules mapped to mouse chromosome 7, syntenic to human chromosome 11, where TRIM family members such as TRIM5, shown to have anti‐viral activity, are localized. A distinct group of TRIM was constitutively expressed in plasmacytoid dendritic cells independently of viral infection or signalling through the type I IFN receptor. Our findings on expression and regulation of TRIM genes in cells of the immune system that have different effector functions in innate and adaptive immune responses, may provide leads for determining functions of this diverse family of molecules.