Negative selection in the thymus includes semimature T cells
Related Experiment Video
Updated: Nov 3, 2026

Examination of Thymic Positive and Negative Selection by Flow Cytometry
Published on: October 8, 2012
1Department of Immunology, IMM4, The Scripps Research Institute, La Jolla, California 92037, USA.
Abstract:
The thymic medulla plays a key role in negative selection (self-tolerance induction) and contains differentiated T cells en route to the extrathymic environment. However, being relatively mature, medullary T cells are thought to be beyond the stage of tolerance induction. This paradox is resolved by the finding that medullary T cells (CD4+8- thymocytes) comprise two distinct subsets. Medullary thymocytes expressing a fully mature (HSAlo) phenotype are strongly resistant to tolerance induction, whereas cells with a semimature (HSAhi) phenotype are tolerance susceptible. These findings suggest that the differentiated T cells reaching the medulla from the cortex remain sensitive to tolerance induction for a brief period before acquiring a fully mature tolerance-resistant phenotype. The semimature subset of medullarsy T cells displays unique requirements for tolerance induction; depending upon the conditions used, tolerizing these cells can involve either a Fas (CD95)-dependent or a Fas-independent pathway.
Related Concept Videos
T Cell Activation and Clonal Selection
Naive T cells that have not yet encountered an antigen express two primary CD...
Primary Lymphoid Organs
The red bone marrow is a soft, spongy tissue nestled in the interior of long bones such as the humerus and femur. It is the site...
Cells of the Adaptive Immune Response
T Cell Types and Functions
Th1 cells stimulate dendritic cells to express necessary co-stimulatory molecules on their surfaces for...
Special Features of Adaptive Immunity
The primary cell types involved in adaptive immunity are T cells and B cells. Each type has a unique role in defending the body against pathogens. T cells are responsible for cell-mediated immunity. They identify and eliminate infected cells directly,...
Development of Immunocompetence
The initial cells that migrate from the fetal thymus settle within the skin and epithelial tissues lining the mouth, digestive tract, and in females, the uterus and vagina. These cells, including skin-based dendritic cells, serve as antigen-presenting cells, playing a key role in T cell activation.
Subsequent T...

