(B) BM from female HYcd4mice on either WT or CCR7 background was mixed with WT female or male BM and transferred into WT female or male recipients. apoptosis in thymocytes with a high affinity for self-peptide/MHC. Despite the importance of clonal deletion, many fundamental questions remain, such as the following: at which stages of development do thymocytes undergo deletion; where does this correspond to anatomically; and what cell types induce apoptosis? The use of different model systems in previous studies aimed at answering these questions has led to conflicting results. The earliest experiments studying unfavorable selection used endogenous superantigens to induce a high-affinity signal. However, this system may provide a qualitatively different transmission than TCR ligation by self-peptide/MHC because of the nature of superantigen acknowledgement. Injection of TCR cross-linking antibodies to simulate a high-affinity transmission has also been used (for review observe reference1). However, this model is usually unlikely to mimic Amisulpride antigen-specific deletion, as it results in high-level glucocorticoid production that causes nonspecific thymocyte death (2). The development of TCR transgenics was a major improvement and allowed for the study of unfavorable selection in response to either exogenous peptide injection or endogenous high-affinity self-antigens (3). Importantly though, WT thymocytes do not express a surface TCR until the double-positive (DP) stage when they rearrange their TCR loci, whereas standard TCR transgenics express both the TCR and TCR chains at the early double-negative (DN) stage. Consequently, unfavorable selection occurs prematurely in TCR transgenics (4), and when the anatomical location of Amisulpride clonal deletion was specifically examined using the F5 TCR transgenic, apoptotic thymocytes were found to be located at the corticomedullary junction (5). More recent studies have made it obvious that early expression of a TCR transgene (68) and the high frequency of antigen-specific T cells in TCR transgenics (9,10) cause a variety of nonphysiological effects. To Amisulpride highlight this point, the HY TCR transgenic model, which has been used extensively to study unfavorable selection, evolves an aberrant populace of thymocytes that are prematurely selected because of early TCR expression (11). The medulla is considered a specialized site for unfavorable selection because of AIRE-mediated expression of tissue-restricted antigens (12), as well as its large quantity of DCs that express a high level of costimulatory molecules such as B7-1/2 and CD40 (1316). Indeed, several strains of mice that lack an organized medulla have severe autoimmune disease (1720). Furthermore, mice deficient for CCR7, a chemokine receptor which is usually important for migration to the medulla (21), develop autoimmune pathology, a result which may be caused by a combination of defective regulatory T cell generation (22), insufficient TCR tuning (23), or incomplete clonal deletion of autoreactive thymocytes (24). Despite the compendium of work implicating the medulla as the primary site of clonal deletion, many thymocytes are predicted COL27A1 to be reactive to ubiquitous self-antigens and would first encounter them in the cortex. Cortical thymic epithelial cells (cTECs) are the predominant stromal cell in the cortex and are essential for positive selection (for review observe research25). Some studies have suggested that cTECs fail to induce tolerance to self-antigens (2630), whereas others have come to the opposite conclusion (3140). Thus, the role of cTECs in central tolerance is usually poorly comprehended. Given this information, we decided to revisit the process of clonal deletion by using the HYcd4model, where antigen-induced unfavorable selection occurs at the DP stage (41). For the first time, we were able to visualize DP thymocytes undergoing clonal deletion in response to an endogenous and ubiquitous self-antigen in vivo. Surprisingly, thymocytes undergoing clonal deletion were found throughout the cortex and were absent from your medulla altogether. Male-reactive DP thymocytes could be recovered in relatively high figures from these mice because of an asynchronous induction of apoptosis. This was likely because of the fact that cTECs, although able to trigger TCR activation, did not efficiently induce apoptosis. As a possible explanation for the delayed induction of apoptosis, we show that apoptotic cells were preferentially associated with CD11c+DCs present throughout the cortex. These results suggest a model where DP thymocytes with high affinity for any ubiquitous self-antigen are first signaled in the cortex but require further stimuli from.