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Early Th 17 responses are necessary to provide protection against Mycobacterium tuberculosis (Mtb). Mtb impedes Th 17 polarization by restricting CD40 co-stimulatory pathway on dendritic cells (DCs). We previously demonstrated that engaging CD40 on DCs increased Th 17 responses. However, the molecular mechanisms that contributed to Th 17 polarization were unknown. Here, we identify the Notch ligand DLL4 as necessary for Th 17 polarization and demonstrate that Mtb limits DLL4 on DCs to prevent optimal Th 17 responses. Although Mtb infection induced only low levels of DLL4, engaging CD40 on DCs increased DLL4 expression. Antibody blockade of DLL4 on DCs reduced Th 17 polarization in vitro and in vivo . In addition, we show that the Mtb Hip1 protease attenuates DLL4 expression on lung DCs by impeding CD40 signaling. Overall, our results demonstrate that Mtb impedes CD40-dependent DLL4 expression to restrict Th 17 responses and identify the CD40-DLL4 pathways as targets for developing new Th 17 -inducing vaccines and adjuvants for tuberculosis., Competing Interests: The authors declare no competing interests., (© 2022 The Author(s).)