The role of T cell help in shaping Dendritic Cell function

Abstract

CD8⁺ T cell priming depends on antigen presentation by dendritic cells (DCs) and their capacity to communicate contextual cues associated with antigen acquisition. DCs often also require additional signals from helper CD4⁺ T cells, which upon mediation via CD40-CD40L further modulate the communication of contextual cue to the responding CD8⁺T cells. The present study was designed to explore the kinetics and molecular mechanisms underpinning this helper- dependent modulation of DC function. <br /> To address this, we employed an <em>in vitro</em> system of bone marrow (BM)- derived equivalents of CD8⁺ DCs (eCD8⁺ DCs) and we assessed the role of different CD40 signalling components in driving their IFN-αA-induced cytokine and chemokine responses by using flow cytometry, mass spectrometry-based proteomics, real time PCR and RNA sequencing. This brought to light remarkable and distinct patterns of gene regulation through which CD4⁺ T cells triggered CD40 and thereby amplified the capacity of IFN-αA to induce or downregulate a broad range of genes. We also observed an unexpected pattern of gene regulation: some genes required both T cell help and IFN-αA stimulations but could not be induced by ‘help’ or IFN-α alone. By varying the exposure time, we further discovered that eCD8⁺ DCs required 1-2 hours of IFN-αA to become responsive to CD40 triggering. Once this pre-activated state was achieved, CD40 stimulation rapidly amplified responses with remarkably fast kinetics. Combining proteomics and RNA sequencing data presented in this thesis suggests a complex interplay between the IFN-αA signalling pathway involving IRFs transcription factors and the NF-κB signalling pathway. <br /> These findings not only reveal new insights into how T cell help adjusts the responsiveness of DC to innate stimuli, but also reveal that this can occur with remarkable speed, which aligns with in vivo imaging studies describing very brief interactions between eCD8⁺ DCs and CD4⁺ T cells during CD8⁺ T cell priming.