Immunology and Microbiology
First Thesis Advisor
Daniel H. Libraty, M.D.
Receptors, Pattern Recognition, RNA Viruses, CD4-Positive T-Lymphocytes, Adaptive Immunity
Virus infection is sensed by the innate immune system through germline encoded pattern recognition receptors (PRRs). Toll-like receptors (TLRs), retinoic acid-inducible gene-I-like receptors (RLRs) and nucleotide-binding oligomerization domain-like receptors (NLRs) serve as PRRs that recognize different viral components. Microbial nucleic acids such as Ribonucleic acid (RNA) are important virus-derived pathogen-associated molecular patterns (PAMPs) to be recognized by PRRs. Virus recognition may occur at multiple stages of the viral life cycle. Replication intermediates such as single-stranded RNA (ssRNA) and double-stranded RNA (dsRNA) are detected by the RNA-sensing PRRs that initiate innate and adaptive immune responses. Triggering of the innate immune system is a critical event that can shape the adaptive immune response to virus infection. Better vaccination strategies that lead to improved T-cell and antibody responses are needed for protection against pathogens. We sought to delineate the RNA-sensing PRR pathways that are activated during infection with an RNA virus, the signaling mediators involved and the influence on subsequent virus-specific adaptive immune responses.
To analyze the role of RNA-sensing PRRs in T-cell immune responses in vitro, we performed direct co-stimulation experiments on CD4+ T-cells of high purity. We utilized synthetic RNA-like immune response modifiers (IRMs) R-848 (MyD88-dependent) and poly I:C (MyD88-independent) as RNA PAMPs to determine the direct effects of RNA-sensing PRR activation on CD4+ T-cells. RNA PAMPs can act directly on CD4+ T-cells and modulate their function and phenotype. Maximal direct co-stimulatory effects were observed in CD4+ T-cells cultured with poly I:C compared to R-848. The cytoplasmic dsRNA-dependent protein kinase R (PKR) was also involved in poly I:C-mediated signaling in CD4+ T-cells.
We found differences in the RNA-sensing PRRs activated by R-848 between mouse and human CD4+ T-cells. We observed minimal direct co-stimulatory effects by R-848 in mouse CD4+ T-cells. In contrast, augmentation of Th1 responses by R-848 was observed in human CD4+ T-cells. TLR8 activation in human CD4+ T-cells may explain the observed differences.
We next explored the signaling pathways activated by RNA PAMPs in conventional dendritic cells (cDCs) and CD4+ T-cells that drive Th1 CD4 T-cell responses in isolated cDC/CD4 T-cell interactions. Allogeneic cDCs and CD4+ T-cells of high purity were cultured together with R-848 and poly I:C in MHC congenic mixed leukocyte reactions (MLRs). R-848 and poly I:C stimulation of type I IFN production and signaling was essential but not sufficient for driving CD4+ Th1 responses. The early production of IL-1α and IL-1β was equally critical.
To analyze the role of RNA-sensing PRRs in T-cell immune responses in vivo, we utilized a mouse model of heterosubtypic influenza A virus (IAV) infections. Using MyD88-/-, TLR7-/- and IL-1-deficient mice, we explored the role of MyD88-signaling in the generation of heterosubtypic memory CD4+ T-cell, CD8+ T-cell and antibody responses. We found that MyD88 signaling played an important role in anti-IAV spleen and lung CD4+ T-cell, spleen CD8+ T-cell and Th1 antibody immune responses. Anti-IAV lung heterosubtypic CD8+ T-cell responses were not dependent on MyD88 signaling.
Our in vitro and in vivo results show the pivotal role of RNA-sensing PRR pathway activation in T-cell immune responses. Understanding the complexity of the PRR pathways involved during viral infections and defining the subsequent immune response would have important implications for the generation of more effective vaccine strategies.
Madera RF. (2012). RNA-Sensing Pattern Recognition Receptors and Their Effects on T-Cell Immune Responses: A Dissertation. Morningside Graduate School of Biomedical Sciences Dissertations and Theses. https://doi.org/10.13028/fcrm-mf40. Retrieved from https://escholarship.umassmed.edu/gsbs_diss/644
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