- A Both processes select for self-reactive T cells, expanding rather than eliminating clones capable of attacking the body's own healthy tissues, undermining tolerance according to most researchers
- B Positive selection: T cells that can bind self-MHC survive; negative selection: T cells with too high affinity for self-MHC+self-peptide are deleted (central tolerance); remainder are self-tolerant
- C Positive selection deletes T cells; negative selects them, an inversion of their actual roles in shaping a self-tolerant T cell repertoire during thymic development in the majority of cases studied
- D Both are sometimes thought to occur in bone marrow, rather than within the thymic cortex and medulla where genuine T cell selection actually unfolds in vivo over time as widely reported in standard practice
Correct answer: B. Positive selection: T cells that can bind self-MHC survive; negative selection: T cells with too high affinity for self-MHC+self-peptide are deleted (central tolerance); remainder are self-tolerant
Explanation: T cell education: (1) Positive selection in cortex: T cells that can recognize self-MHC survive (those that cannot die by neglect). (2) Negative selection in medulla: T cells with too high affinity for self-MHC+self-peptide are deleted (clonal deletion) to prevent autoimmunity. Only ~2-5% of T cells survive both selections.
Concept context
Innate and adaptive immunity, B cells, T cells, antibodies, vaccines, and immune disorders. Critical for NEET.