The in vivo inhibitory fucntion of the MHC-I a3 domain/CD8a interaction 2329318

Introduction Since the discovery of the MHC-I α3 domain/CD8α interaction approximately 40 years ago, numerous in vitro studies have demonstrated that this binding stabilizes the MHC-I/TCR complex and facilitates signaling for low-affinity or CD8-dependent TCRs. However, the in vivo significance of this interaction has remained largely unexplored. In this abstract, we present our recent findings regarding the in vivo blockade of the MHC-I α3 domain/CD8α interaction in both the absence and presence of antigen exposure. Methods We employed monoclonal antibodies directed against the α3 domain of MHC class I to selectively disrupt the interaction between the MHC-I α3 domain and CD8α. Specifically, two monoclonal antibodies targeting the α3 domains of H-2Kb and H-2Db were used in C57BL/6 mice. In addition, three monoclonal antibodies specific for the α3 domains of H-2Ld, H-2Dd, and H-2Kd were utilized in the BALB/c mice. These α3 domain—specific antibodies enable precise interrogation of MHC-I α3 domain—CD8α interactions under both antigen-dependent and antigen-independent conditions. Results Our results demonstrate that selective blockade of individual MHC-I α3 domain—CD8α interactions is sufficient to activate CD8+ T cells in the absence of antigen exposure. In the presence of antigen, blockade of either the H-2Db or H-2Kb α3 domain—CD8α interaction enhances ovalbumin peptide—induced, H-2Kb—restricted OT-I CD8+ T cell responses and prevents the development of CD8+ T cell tolerance. Importantly, blockade of either the H-2Db or H-2Kb α3 domain—CD8α interaction also reverses established H-2Kb—restricted OT-I CD8+ T cell tolerance. Conclusion These data suggest that the MHC-I α3 domain—CD8α interaction delivers an inhibitory signal to CD8+ T cells in vivo during antigen-independent homeostasis. In the presence of antigen, this interaction also plays an inhibitory role in vivo at multiple stages of CD8+ T cell activation.