Yes, LYMPHOKINE is a Scrabble word!

Letter values in Scrabble US: L 1, Y 4, M 3, P 3, H 4, O 1, K 5, I 1, N 1, E 1.

Is it a valid word?

LYMPHOKINE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a cytokine secreted by helper T cells in response to stimulation by antigens and that acts on other cells of the immune system (as by activating macrophages)