Chapter 24, Problem 1P

44322-24-1P

Summary Introduction

To examine: Whether the statement “T cells whose receptors strongly bind a self-peptide-MHC complex are killed off in peripheral lymphoid organs when they encounter the self peptide on an antigen-presenting dendritic cell” is true or false.

Introduction: Immunological tolerance is the state of unresponsiveness to a particular antigen due to an earlier exposure to the same antigen. There are two types of immunological tolerance: central tolerance and peripheral tolerance. Any defect in immune self-tolerance causes autoimmune diseases.

Answer to Problem 1P

Correct answer: The statement is true.

Explanation of Solution

The host immune system in normal conditions is able to avoid responding to normal cells and molecules. Refer to Fig. 24-21 “Mechanisms of immunological self-tolerance” in the textbook. Several mechanisms in the central lymphoid organs and peripheral lymphoid organs are involved in the self-tolerance of immune cells, including receptor editing, clonal deletion, clonal inactivation, and clonal suppression.

For the activation of the T lymphocytes in the peripheral lymphoid organs, it requires co-stimulatory immune signals generated by helper T cells (T_H cells), when pathogens are present. In normal conditions, a self-reactive T cell does not generate these co-stimulatory immune signals and fails to get activated. Instead, it gets inactivated, suppressed by a regulatory T cell or killed.

Thus, in the peripheral lymphoid organs, if a T lymphocyte binds to a self-peptide-MHC complex presented on an antigen-presenting cell (APC) such as dendritic cell, it would be killed by the mechanisms of immune self-tolerance.

Hence, the statement is true.