Following Treg contact, the typical release of calcium ions into the plasma of helper cells does not occur.
In the English language usage of medicine and biology, plasma is the fluid part of blood and lymph, not the formed elements, i.e. red blood cells, white blood cells and platelets. Maybe it was lost in the translation from German.
The fliud content of cells is called cytosol from the solution portion of the cells minus the cells' organelles, e.g. nucleus, mitochondria, endoplasmic reticulum, ribosomes, etc.
The DOI from the press release gave me this citation:
N.B. The Greek letters for kappa and beta that modify that particular nuclear factor, NF kappa beta were not copied.
FWIW:
“The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment.”
http://en.wikipedia.org/wiki/Cell_Membrane