Complete the sentences to review the process of T-cell activation. Then move the sentences into the correct order. T-cell activation begins when an ____________ delivers antigen to a CD4 or CD8 T cell. In contrast, ____________ T-cell activation requires the action of ____________ cells in order to differentiate into memory CD8 cells and activated CD8 cells. In the case of a ____________ cell, it can differentiate into T helper ____________ cells which will activate ____________ cells. Activated CD8 cells will mount a direct attack on target cells through the action of ____________ , which punch holes in membranes, and ____________ , which then enter through these passageways. It may also differentiate into a T helper ____________ cell for B-cell activation, or T helper ____________ or T regulatory cells for modulation of the ____________ response.