STX11 encodes syntaxin 11, a SNARE protein that mediates vesicle fusion and membrane trafficking processes critical for immune cell function. The protein facilitates fusion of cytotoxic granules with plasma membranes at immunological synapses in CD8+ T cells and NK cells, enabling cytotoxic granule exocytosis 1. STX11 also regulates CD107a and CD40L surface mobilization and cytokine secretion in CD4+ T cells, supporting T cell-B cell interactions and humoral immunity 1. Beyond immune function, STX11 undergoes dynamic palmitoylation that controls fatty acid uptake in muscle stem cells by facilitating CD36 translocation through SNARE complex formation, promoting muscle regeneration 2. Pathogenic variants in STX11 cause familial hemophagocytic lymphohistiocytosis type 4 (FHL-4), a severe hyperinflammatory syndrome with high mortality 34. STX11 deficiency impairs both cytotoxic function and humoral immunity, as patients exhibit hypogammaglobulinemia and altered B cell populations 1. Mutations in STX11 represent a significant portion of genetic HLH cases, accounting for part of the degranulation defect genes that collectively comprise >50% of diagnosed cases 4. The protein's diverse roles in immune cell degranulation, T-B cell interactions, and tissue regeneration highlight its importance in both innate and adaptive immunity.