Research Interests

Genital mucosal DC: Herpes simplex virus

Keratinocytes infected with herpes simplex virus-2 are in close proximity to the Langehans' cells within the vaginal epithelial layer Cryosection of vagina of mouse infected for 18h with HSV-2 was stained with antibody to HSV-2 (red), MHC Class II (green) and nuclei were visualized with DAPI (blue).

Langerhans' cells (green) in the epithelial layer is in close proximity with HSV-infected keratinocytes (red). L=lumen of vagina. One of the laboratory's major interests is to understand the mechanism of immune induction at the natural route of infection to herpes simplex virus (HSV) type 2 infection. HSV-2 is one of the most common sexually transmitted diseases with a prevalence of approximately 45 million in the United States. Currently, the mechanism for immune induction to HSV-2 in the genital mucosa is unknown. The examination of the immune responses induced in the female genital tract must take into account that, unlike other mucosal surfaces, it undergoes hormone-dependent changes over the course of the estrous cycle. Thus, our laboratory is currently studying the dendritic cells within the vaginal mucosa and comparing their phenotype, localization and function at different estrous stages in order to understand the mechanism of immune induction at this special site. A key question in this regard relates to the role of the antigen-presenting cells, particularly, the dendritic cells. Mice are susceptible to genital HSV-2 infection only during the diestrous phase. We have recently found a previously unanticipated role of submucosal dendritic cells in Th1 induction to herpes simplex virus-2 infection in the progesterone-dominant female mice. Our specific goals are to understand 1) how dendritic cells recognize the virus and become activated, particularly the role of toll-like receptors in viral recognition, 2) what determines the ability of the dendritic cells to elicit specifically Th1 and not Th2 responses, 3) what factors are responsible for the recruitment of these relevant dendritic cells, and 4) what other cells of the innate immunity are involved in the generation of protective Th1 responses to HSV-2. In this regard, we have identified that HSV-2 and HSV-1 are both recognized by Toll-like receptor (TLR) 9 within plasmacytoid dendritic cells. This recognition is required for the plasmacytoid dendritic cells to secrete high levels of type I interferons which mediate antiviral functions. Further, we also discovered that TLR recognition of HSV-2 infection in vivo occurs in two steps, the first recognition is mediated by the infected stromal cells and the second mediated by the uninfected dendritic cells. Remarkably, both steps of TLR-mediated viral recognition are required for the generation of antiviral TH1 immunity. We hope that by understanding the mechanism of immune generation to HSV-2 we will be able to design effective vaccines against HSV and other sexually transmitted disease agents.

Intestinal DC: Salmonella typhimurium

Previously, we have characterized three major populations of DCs in the Peyer's patches, which are the primary immune inductive organ in the gastrointestinal mucosa. The three DC populations reside in distinct anatomical locations within the Peyer's patch, and secrete distinct sets of cytokines and influence T helper cells to differentiate into either Th1 or Th2 cell types (see diagram on the right). The first type of DCs, called myeloid DCs (CD11b+), reside in the subepithelial dome just underneath the follicle-associated epithelium. The myeloid DCs of the Peyer's patch are special compared to their counterpart in other lymphoid organs in that they have the ability to secrete high levels of IL-10 (not IL-12) and induce IL-4 and IL-10 secretion from CD4+T cells. These cells localize in the subepithelial dome region by responding to the chemokine MIP-3 secreted from the follicle-associated epithelium. The second type of DCs, lymphoid DCs (CD8+), localize exclusively in the interfollicular region. This area contains most of the T cells in the Peyer's patch, and DCs can be seen in close proximity with T cells. The lymphoid DCs localize in the T cell region by responding to the chemokines MIP-3ß and SLC. Finally, we have identified a new subset of DCs called double negative (DN) DCs. These cells lack the expression of both lymphoid (CD8) and myeloid (CD11b) markers and they are localized in the subepithelial dome, interfollicular region and in the epithelium. These DN intraepithelial DCs are found in close contact with M cells, which are specialized in taking up luminal antigens into the dome region. Both the DN and lymphoid DCs secrete IL-12 and influence naïve T cells to become Th1 effector cells.

Our goal is to define the mechanisms of T cell priming within the Peyer's patch following infection by naturally occurring intestinal pathogen such as Salmonella typhimurium. This infection is characterized by the differentiation of Th1 cells, and the protection observed is conferred by IFN-mediated mechanism. Specifically, we would like to understand how the three dendritic cell subsets in the Peyer's patch induce such effector T cells, and where the initiating events are taking place in vivo.

Lung DC: Influenza infection

The most effective measure of prevention of infectious agents is the prophylactic vaccines. For vaccine development, it is necessary to understand the requirement for optimal induction of adaptive immunity. Epidemics of influenza result in ~36,000 deaths each year in the USA alone. The devastating impact of the 1918 influenza pandemic, which killed ~21 million people worldwide, provides a stark illustration of the potential consequences of the emergence of natural mutations and recombination in the influenza genome. Influenza virus is transmitted through inhalation and direct contact, and infection and replication occurs within the columnar epithelium lining the respiratory tract. Th1 immunity can provide protection against influenza infection. One of the focus of this laboratory is to understand how various DC populations in the lungs mediate the initiation of adaptive immune responses to influenza virus infection. Through examination of the basic mechanisms by which adaptive immunity is induced following natural viral infections in vivo, we wish to contribute to better vaccine design.