In the Study by Green Et Al

In the study by Green et al. (2002) , PHA-stimulated lymphocyte proliferation in a fixed number of lymphocytes fell after a one-hour intensive treadmill run but what happened to the proliferative response when natural killer cells were removed from the proliferation cultures?

A) Proliferation was the same as in the cultures where NK cells were present
B) Proliferation was higher than in the cultures where NK cells were present
C) Proliferation was lower than in the cultures where NK cells were present
D) Proliferation was no longer detectable
E) None of the above