A novel non‑contact communication between human keratinocytes and T cells: Exosomes derived from keratinocytes support superantigen‑induced proliferation of resting T cells.

It is widely accepted that keratinocytes act as non‑professional antigen‑presenting cells and support superantigen‑induced proliferation of resting T cells; however, it remains unknown whether keratinocytes function in situ with T cells via a non‑contact mechanism. The current study used a transwell co‑culture system and demonstrated, for the first time to the best of the authors' knowledge, that HaCaT cells (the human keratinocyte cell line) did induce T cell proliferation via indirect contact. The data further indicated that exosomes, small membrane vesicles that transfer antigens to recipient cells, are also involved in the superantigen‑associated immunity of keratinocytes. The current study provided experimental evidence that HaCaT‑exosomes contained MHC I and II, and could interact with T cells. In addition, following interferon γ stimulation, Staphylococcal aureus enterotoxin B‑loaded HaCaT cells secreted exosomes to induce the proliferation of CD4+ and CD8+ T cells in vitro. This novel biological function of exosomes reveals a new mechanism of how keratinocytes participate in bacterial superantigen‑induced immune responses.