Question

Which of the following statements are true of a T cell that expresses two α chains (and thus two different T-cell receptors) as a result of ineffective allelic exclusion of the α chain during rearrangement? (Select all that apply.)

a. Engaging either of the T-cell receptors on MHC molecules of the thymic epithelium will result in positive selection.
b. One of the T-cell receptors will be functional while the other will most probably be non-functional.
c. If either T-cell receptor binds strongly to self-peptides presented by self-MHC molecules, the thymocyte will be negatively selected.
d. One of the T-cell receptors may be autoreactive but escape negative selection because its peptide antigen is present in tissues other than the thymus.
e. Subsequent gene rearrangements may give rise to a γ:δ T-cell receptor.

Answer 1

If a T cell expresses two α chains due to ineffective allelic exclusion, several statements are true including positive selection upon engaging with MHC molecules, one functional and one non-functional T-cell receptor, negative selection if self-peptides are recognized too strongly, and the possibility of having a γ:δ T-cell receptor.

Step-by-step explanation:

If a T cell expresses two α chains as a result of ineffective allelic exclusion, several statements are true. First, engaging either of the T-cell receptors on MHC molecules of the thymic epithelium will result in positive selection. This means that T cells that can bind to MHC molecules are selected to continue development. Second, one of the T cell receptors will be functional while the other will most probably be non-functional. This is because during rearrangement, one α chain is successfully rearranged while the other is not. Third, if either T-cell receptor binds strongly to self-peptides presented by self-MHC molecules, the thymocyte will be negatively selected. T cells that bind too strongly to self-antigens are eliminated to prevent autoimmunity. Fourth, one of the T-cell receptors may be autoreactive but escape negative selection if the peptide antigen it recognizes is present in tissues other than the thymus. Finally, subsequent gene rearrangements may give rise to a γ:δ T-cell receptor, which is an alternative type of T-cell receptor.