Specific immunity, T cells

There are two types of T cells which involved in the specific immunity. One type is cytotoxic T cell or killer T cell. In this case when pathogen enter the cell, and that cell moves the protein to its surface, a patrolling T cell recognizes and binds to this protein and release profferrin, a protein which raptures a membrane of the infected cell. T cell can destroy a cancer cell.
The second type of T cell is helper T cell. The role of helper T cell is to activate B cell. The B cell that responses has the same antigen that activates the helper T cells. The T cell sends out chemical signals that effect various immune cells. These chemicals stimulate B cells to divide and produce a clone of antibody releasing cells.

http://www.youtube.com/watch?v=tqjhMHG7J08&feature=related