Surface proteolytic activity in cell interactions: activation of human peripheral lymphocytes in contact with...

The transformation of lymphocytes by mitogens or by periodate treatment requires the presence of glass-adherent leukocytes. We have demonstrated that contact with periodate-treated adherent cells transforms human peripheral T lymphocytes. Using a new method to estimate proteolytic activity released by cells or available at cell surfaces, we found marked stimulation of cell surface-associated enzyme activity on glass-adherent cells treated by NaIO4 or by Con A. The expression of this enzymatic stimulation required contact with substrate, just as the transformation of untreated T cells required contact with treated adherent cells. Therefore, we propose that cell-cell interaction leads to an efficient mode of stimulation, which may be mediated by or initiated by surface-associated proteases of adherent cells.