POST-IT has led to the following technological developments and state of the art knowledge. First, the development of a new technique for measuring the intracellular sorting of organelles. We used this technique to characterize the cellular phenotype of a novel genetic disease caused by a mutation in an alternative starting codon in the gene coding for an organelle trafficking protein. Second, we developed a new approach for measuring activation of T cells, which is more sensitive than other assays. Third, we generated a comprehensive set of plasmids for measurement of pH in organelles. Given the large importance of pH regulation in both cell biological and (bio)chemical processes, this will be valuable to the broad cell biology and biochemistry communities. Using this toolset, we discovered a new cell biological mechanism: that organelles can be heterogenous is composition. This finding provides an important new insight in the intracellular processing of different pathogens by immune cells. Finally, using a screening approach, we discovered a key protein that becomes phosphorylated upon recognition of bacteria, but not upon healthy self-material. Using the approaches above, we are currently following up on this finding as this might explain how macrophages can selectively present fragments of ingested microbes, but not harmless self-material, to T cells.