Thymocytes that bind self-antigen at the junction between cortex and medulla are killed by apoptosis. What is this step called?

1. Thymocytes arrive in the cortex of the thymus as double negatives, carrying neither the CD4 nor the CD8 molecule. 2. In positive selection they bind the MHC molecules on the thymic epithelia, and the MHC molecules of self are selected for. 3. The survivors become double positives carrying both CD4 and CD8 and move to the junction between cortex and medulla. 4. There, professional antigen-presenting cells bring self-antigens into the thymus from other parts of the body. 5. T cells that bind those self-antigens are selected against and killed by apoptosis, which is negative selection. 6. Positive selection names the earlier MHC-binding step, so it points at the wrong stage of development. 7. Clonal deletion and clonal anergy describe how self-reactive B cells are handled in the bone marrow, not thymocytes. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 21 "The Lymphatic and Immune System", section 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types_