In order to fuse lytic granules (LGs) with the plasma membrane at the immunological synapse, cytotoxic T lymphocytes (CTLs) have to render these LGs fusion-competent through the priming process. In secretory tissues like brain and neuroendocrine glands this process is mediated by members of the Munc13 protein family. In human CTLs mutations in the Munc13-4 gene cause a severe loss in killing efficiency, resulting in familial hemophagocytic lymphohistiocytosis type 3 (FHL3) suggesting a similar role of other Munc13 isoforms in the immune system. Here, we investigate the contribution of different Munc13 isoforms to the priming process of murine CTLs. We demonstrate on both mRNA and protein level that Munc13-1 and Munc13-4 are the only Munc13 isoforms present in mouse CTLs. Both isoforms rescue the drastical secretion defect of CTLs derived from Munc13-4-deficient Jinx mice. Furthermore mobility studies of LGs performed with TIRF micrscopy indicate that Munc13-4 as well as Munc13-1 are responsible for the priming process of LGs. Even more the domains of the Munc13 protein which are responsible for functional fusion could be identified. We conclude from these data that both isoforms of the Munc13 family are functionally redundant and identify Munc13-1 as an alternative target for immunotherapy in patients suffering from FHL3.
- Copyright © 2013 by The American Association of Immunologists, Inc.