Getting secretory granules ready for prime time

Several rare human diseases have shed important light on the secretory pathway required for lymphocyte cytotoxicity. In this issue of Cell, Feldmann et al. identify mutations in Munc13-4 as a cause of familial hemophagocytic lymphohistiocytosis. Munc13-4 appears to be involved in the priming of cytotoxic granules prior to fusion with the plasma membrane.