Without that second signal, the T cells will refuse to respond to the protein fragment they were shown.

And that question can be answered only when scientists discover the normal function of the protein fragments.

The protein fragment was synthetic to avoid the possibility that something in a live cell might have contributed to the disease.

But such a protein can sometimes fall apart into the original protein fragments.

C5a is a protein fragment released from complement component C5.

In a healthy brain, these protein fragments are broken down and eliminated.

They could recognize protein fragments but not kill the cells.

Another chemical test suggested that the heme was attached to a protein fragment.

Each T cell has a slightly different shape so every size and shape of protein fragment can be recognized.

Without the drug, the protein fragments would float helplessly in the cell.