Tpl2 Signaling Regulates Dendritic Cell Activation and Responding T Cell Differentiation Following <i>Mycobacterium tuberculosis</i> Infection

Abstract Mycobacterium tuberculosis (Mtb) utilizes a number of immune evasion mechanisms in order to persist inside of host antigen-presenting cells. Dendritic cells (DCs) are important in restricting Mtb growth by migrating to draining lymph nodes and activating antigen-specific T cell responses, but the roles of DCs in Mtb infection require further study. This study investigated DC activation and functional outcomes following Mtb H37Ra-driven tumor progression locus 2 (Tpl2) signaling. The role of Tpl2 was interrogated genetically, utilizing bone marrow-derived DCs from Tpl2−/− mice. We assessed cytokine production via ELISA, mRNA levels via qRT-PCR, and expression of cell surface molecules via flow cytometry. In Mtb-treated DCs, genetic depletion of Tpl2 increased production of pro-inflammatory cytokines such as IL-12p40 and IL-6. Loss of Tpl2 in Mtb-treated DCs also led to decreased E-cadherin expression, and increased expression of Icam-1 (Cd54) and Mmp2, which are molecules involved in DC transmigration. Expression of Ccr7 and Ccr4 was also enhanced in Mtb-treated Tpl2−/− DCs, which correlated with improved migration of Tpl2−/− DCs towards CCL19 and CCL21 in vitro (assessed using a trans-well assay). When antigen-specific CD4+ T cells were co-cultured with Mtb-infected DCs, deletion of Tpl2−/− in the DCs resulted in increased T cell production of IFNγ and IL-2, as well as increased Tbet expression, indicative of enhanced Th1 polarization. Together, these data indicate that Mtb-induced Tpl2 signaling suppresses certain aspects of DC activation, leading to blunted Th1 responses against the pathogen.