DOCK8 deficiency diminishes thymic T-regulatory cell development but not thymic deletion

Abstract

Objective: To define the effect of DOCK8 deficiency on thymic tolerance in mice.

Methods: Thymocytes from wild-type (Dock8^+/+ ) and DOCK8-deficient (Dock8^pri/pri ) mice were examined by flow cytometry. Some mice had transgenic expression of the BCL2 anti-apoptotic protein in haemopoietic cells. Some mice expressed the transgenic 3A9 T-cell receptor (TCR), which triggers thymocyte deletion in mice also expressing hen egg lysozyme under the insulin promoter.

Results: In Dock8^pr/pri mice, the proportion of thymocytes induced to acquire tolerance at the immature CCR7^- stage was normal. Deletion of strongly self-reactive CD4⁺ thymocytes occurred efficiently in Dock8^pri/pri mice in a TCR-transgenic model that requires self-antigen transfer from epithelial cells to bone marrow (BM)-derived antigen-presenting cells. Thymic Foxp3⁺ T-regulatory cells (T_REG) and Helios⁺ Foxp3^- T_REG precursors were decreased in Dock8^pri/pri mice, including when apoptosis was inhibited by BCL2 transgene expression. Dock8^pri/pri thymic T_REG expressed CD25 and CTLA-4 at normal levels. The results suggest that DOCK8 deficiency does not affect the function of BM-derived antigen-presenting cells in the thymus, the TCR self-reactivity threshold that activates tolerance mechanisms in thymocytes or the apoptotic deletion of these thymocytes. However, DOCK8 is required to prevent a subset of developing T_REG cells from undergoing cell death via a mechanism that is distinct from apoptosis.

Conclusion: DOCK8 deficiency diminishes T_REG development in the thymus without compromising thymocyte deletion.

Keywords: T‐cell deletion; T‐cell selection; T‐cell tolerance; T‐regulatory cells; dedicator of cytokinesis 8 (DOCK8); thymus.