Research & Publications
The mucosal surfaces represent major sites of entry for numerous infectious agents. Consequently, the vast mucosal surfaces are intricately lined with cells and lymphoid organs specialized in providing protective antibody and cellular immunity. We focus on understanding how viruses are recognized by the cells of the innate immune system and how that information is used to generate protective adaptive immunity. We study immune responses to herpes simplex viruses and Zika viruses in the genital tract and influenza virus and rhinovirus infection in the lung. Our studies probe the mechanism of protection provided by the memory T cells that reside within the mucosal organs, known as tissue resident memory T cells, and use this information to design better vaccines. We developed a new vaccine strategy, "Prime and Pull" in which memory T cells can be established at the mucosal surface targeted by viruses. Prime and Pull confers better protection against genital herpes than conventional vaccine approaches. Our ultimate goal is to utilize the knowledge we gain through these areas of research in the rational design of effective vaccines or microbicides for the prevention of transmission of viral pathogens and possible treatment of cancers.
Specialized Terms: Innate immunity; Autophagy; Inflammasomes; Sexually transmitted infections; Herpes simplex virus; Human papillomavirus; Respiratory virus infections; Influenza infection; T cell immunity; Commensal bacteria
Extensive Research Description
Our research addresses mechanisms of innate recognition of viruses and initiation of antiviral immunity, particularly at the natural site of virus encounter at the mucosal surfaces.
Innate virus recognition, autophagy and signaling: The innate immune system has evolved to recognize invading pathogens through pattern recognition receptors (PRRs). Because viruses are synthesized by the host cell machinery, the nature of viral signatures recognized by PRRs was unclear. Our research revealed that viral nucleic acids from dsDNA and ssRNA viruses serve as a viral signature, and that they are recognized by endosomal Toll-like receptors (TLR)-9 and TLR-7, respectively in plasmacytoid dendritic cells (pDCs). Further, we demonstrated that in vivo, pDCs are required to secrete type I IFNs in response to genital herpes infection and mediate innate protection of the host. We discovered the role of autophagy in innate viral recognition. We demonstrated that TLR-7-mediated recognition of certain ssRNA viruses requires transport of cytosolic viral replication intermediates into the endosome by the process of autophagy in pDCs. This study demonstrated a link between innate viral recognition and autophagy. Unlike the pDCs, most other cell types recognize virus infection via the RIG-I-like receptors (RLRs) within the cytosol. In a recent study, we demonstrated that autophagy regulates RLR pathway by removal of damaged mitochondria. In the absence of autophagy, reactive oxygen species (ROS) accumulate within the mitochondria, and turn off regulation of RLR signaling. Thus, autophagy is essential in 1) delivering viral ligands to endosomal TLRs, and 2) clearing damaged mitochondria and ROS, thus regulating RLR signaling. We are currently investigating the mechanism by which ROS regulates RLR signaling. More recently, we identified a lysosome-related organelle from which both TLR7 and TLR9 traffic to signal for interferon production and demonstrated that TLR traffic to this compartment is mediated by the adaptor protein AP-3. AP-3 recruitment to the TLR9 endosome requires activity of PIKfyve, an enzyme that phosphorylates PI3P to form PI(3,5)P2 on endosomal membrane.
Temperature control of innate immune response to viruses: we found that temperature can alter the ability of the airway cells to mount an effective innate immune response against rhinovirus, the common cold virus. Airway epithelial cells, the cells that form the lining of the nose and the other airways, are the main target of rhinovirus infection. In order to amplify, spread, and cause disease, the virus must enter these cells and make more copies of itself. By studying airway cells incubated at different temperatures, we discovered that mechanisms used by the innate immune system to protect cells against this virus are quite effective at core body temperature (37°C), but are greatly diminished at slightly cooler temperatures, such as temperatures that might be found in the nasal passages upon inhaling cool ambient air (33°C). The temperature-dependent signals included those involved in the recognition of the replicating virus inside the cell (the RIG-I like receptor pathway) as well as the signals required for turning on antiviral defenses following viral recognition (the Type I interferon response.) These signals are important in immune defense against many viruses, and future studies may reveal that lower temperature provides an opportunity for other viruses that infect the airways or other cool areas of the body to evade antiviral defenses.
Adaptive immunity to viruses: Innate recognition of viruses allows activation of adaptive immune responses. Dendritic cells (DCs) are potent inducers of T cell responses. However, how various populations of DCs sense virus infection and induce immune responses during a natural virus infection is unclear. OUr study demonstrated that submucosal DCs (beneath the epithelial layer), but not Langerhans cells (within the epithelial layer), are the primary inducers of Th1 immunity following genital herpes infection. Antigen presentation following mucosal viral infection is handled by the tissue-migrant submucosal DCs, while needle-introduced virus antigens are presented by lymphoid resident DCs . In addition to the direct activation of DCs by TLRs, we showed that DCs require TLR-dependent instructive signals from the infected cells in order to induce differentiation of effector T cells. We further demonstrated the requirement for TLR-dependent signal in enabling maximum screening of cognate lymphocytes during initiation of adaptive immunity through remodeling of the lymph node arteriole. Once initiated within the lymph nodes, effector Th1 cells travel to the site of infection and eliminate virus infection. Our recent study showed that the local mucosal DCs and B cells cooperate to restimulate Th1 cells to execute protective antiviral immunity. These studies collectively demonstrated the importance of tissue-DC interaction in the initiation of antiviral immunity. While the role of TLRs and RLRs in the initiation of adaptive immunity has been studied extensively, the role of NOD-like receptors (NLRs) in innate viral recognition and initiation of adaptive immune responses is unknown. Our recent study demonstrated that influenza virus infection triggers NLRs and it is required to elicit protective T cell and B cell immunity. We are currently using this information to design and develop novel vaccine strategies to better fight viral infections including HSV-2, influenza and human papillomavirus.
Tissue resident memory T cells: Adaptive immune response to pathogens generates effector T cells with diverse functions. While the majority of effector T cells engage in pathogen control during primary infection, a subset of effector T cells differentiates into memory T cells critical for controlling future infections. Recent studies have revealed that a small subset of effector T cells seed the lymphoid and non-lymphoid tissues and establish residency. Precursors of tissue-resident memory T cells (TRM) receive critical cues from the tissue for migration and residency. We demonstrated that CD4 T cells 'help" the CD8 T effector cells enter the tissue through their secretion of IFN-g and induction of CXCL9 and CXCL10 that bind to CXCR3 expressed by teh CD8 effector T cells. We also demonstrated that TRM can reside within the epithelial layer, or be housed subepithelially in a structure known as memory lymphocyte clusters (MLCs). MLCs are self-sustaining home to the TRMand are supported by the local macrophages that secrete retention signals. Importantnly, CD4 and CD8 TRM provide potent protection against viral challenge compared to circulating memory counterparts. Based on this understanding, we developed a new vaccine strategy we call "Prime and Pull". This vaccine works in two steps. First, we prime T cell responses using conventional vaccines. Second, we "pull" in the T cells to the organ of choice using chemokines that we now know are capable of recruiting such cells (CXCL9 and CXCL10). The Prime and Pull vaccine provides much better protection against genital herpes infection than conventional vaccine alone, because it establishes CD8 TRM at the site of pathogen entry. This understanding for CD8 T cell access can be harnessed to enable T cell entry into solid tumors, which has direct implications for cancer immunotherapy.
Arboviruses; Autophagy; DNA Viruses; Herpes Simplex; Immune System; Immunity, Cellular; Immunity, Innate; Influenza, Human; Molecular Biology; Pneumonia, Viral; Pregnancy Complications; Proviruses; RNA Viruses; Sexually Transmitted Diseases; Tumor Virus Infections; Encephalitis, Viral; Central Nervous System Viral Diseases; Inflammasomes