Which one of the following statements regarding positive and negative selection of T cells is NOT true?
A)Thymic epithelial cells present self-peptide-MHC to developing T cells undergoing the selection process.
B)T cells that do not recognize self-peptide-MHC die by neglect.
C)T cells that bind too strongly to self-peptide-MHC die by Fas ligand-mediated apoptosis.
D)During positive selection,developing T cells express higher levels of anti-apoptotic proteins such as bcl-2.
E)A breakdown in negative selection may result in the development of some autoimmune diseases.

Question

Quizplus · Accepted Answer

Developing T cells that bind with high avidity to self peptide-major histocompatability complex (MHC)in the thymus are deleted by negative selection.This process is mediated by signaling through the T cell receptor via a poorly understood pathway,but it does not involve the Fas ligand.Thymic epithelial cells,as well as professional antigen-presenting cells in the thymus,present peptide-MHC to developing T cells,generating signals that promote survival.This is called "positive selection" and results in increased expression of bcl-2.Rare autoimmune diseases,such as autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED),may result from failure of central negative selection.

Which One of the Following Statements Regarding Positive and Negative