Immunologists have captured the process in which developing killer T-cells are tested by dendritic and other cells to see if they react to normal proteins(self-antigens) from the body. This safety check insures that the T-cells don't harm normal cells in the body and cause autoimmune disorders.

See the source article by following the link below:
Immunologists have captured the process in which developing killer T-cells are tested by dendritic and other cells to see if they react to normal proteins(self-antigens) from the body. This safety check insures that the T-cells don't harm normal cells in the body and cause autoimmune disorders.