Ksp37 is a rapidly mobilized NK cell secretory protein that engages FGF2

Ksp37, a 37 kDa secretory protein abundant in differentiated CD56dim natural killer cells, is rapidly mobilized and secreted in a dose-dependent, JAK-1–dependent manner.

• Why it matters: NK cells need fast, preloaded effector responses, but the activation-linked behavior and extracellular roles of this previously unexplored secretory protein were unclear.
• What they did: The study characterized Ksp37 secretion kinetics under low cytokine stimulation, assessed replenishment after release, mapped its storage to polarized compartments distinct from granzyme B and perforin, and tested binding to fibroblast growth factor 2 (FGF2).
• The result: Ksp37 secretion is sensitive to low cytokine levels and is replenished quickly for continued responsiveness, and its novel FGF2 binding suggests NK cells may modulate the FGF2–FGFR1 axis.

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