The impact of short CYLD in medullary thymic epithelial cell development (P1425)

Abstract

Abstract CYLD is a deubiquitinating enzyme and acts as a negative regulator of NF-κB signaling. To analyse the function of CYLD in vivo we used CYLDex7/8 mice, which are characterized by loss of the full-length transcript and overexpression of a short splice variant of cyld (sCYLD). In these mice thymic and peripheral CD4 and CD8 T cells were reduced compared to controls. Hence, we were interested to investigate the contribution of CYLD in positive and negative selection in the thymus in vivo. For this purpose we crossed the HY-TCR transgene (HYtg) to CYLDex7/8 mice. The analysis of CYLDex7/8 HYtg males revealed an increase in CD4+CD8+ DP as well as in CD8 SP thymocytes, suggesting a less pronounced negative selection in CYLD mutant mice compared to HYtg control mice. Since medullary thymic epithelial cells (mTECs) play an essential role in the negative selection process of thymocytes, the levels of mTECs in the medullary compartment were examined by histology and FACS analysis. We observed reduced numbers of mTECs, combined with decreased expression levels of the mTEC markers UEA-1, keratin-5, claudin-3 and claudin-4. Interestingly, specifically immature mTECs were significantly reduced compared to controls, suggesting a developmental block in the transition of immature to mature mTECs. Taken together, these results display a crucial role of sCYLD in the development and maturation of mTECs.