The Role of B7-CD28 and CD40L-CD40 costimulatory signaling in thymic Invariant NKT Cell subset development

Abstract

Abstract Invariant Natural Killer T (iNKT) cells are a unique subset of NKT cells that express a highly restricted αβ T cell receptor (TCR) and are selected in the thymus by recognition of Glycolipid/CD1d complex expressed by double-positive thymocytes. We previously demonstrated that thymic iNKT cell development is highly sensitive to B7-CD28 costimulatory interactions, with substantially decreased numbers of thymic iNKT cells in B7 and CD28 knockout mice. Advances in iNKT subset identification have allowed the detailed study of three major iNKT subsets, NKT1, NKT2, and NKT17, defined by characteristic transcription factor expression. We have analyzed the requirement for B7-CD28 and CD40-CD40L costimulatory signaling for development of thymic iNKT subsets. Comparison of BALB/c wild-type, B7 knockout, and CD28 knockout mice showed a substantial decrease in number of all thymic iNKT subsets in B7 and CD28 knockouts, demonstrating a critical role for B7-CD28 signaling in development of all thymic iNKT subsets. In contrast, CD40 knockout and CD40L knockout mice showed a substantial selective decrease in NKT2 cells with less effect on NKT1 and NKT17 subsets. These findings identify distinct requirements for B7-CD28 costimulation in thymic development of all iNKT subsets and for CD40L-CD40 costimulation selectively in NKT2 subset development. Further experiments are currently in progress examining the cellular requirements for B7 and CD40 expression in NKT development using conditional B7 and CD40 knockouts and complementary bone marrow mixed chimera approaches.