Vermont Center for Immunobiology and Infectious Disease

Research Lab of Ralph Budd, M.D.

Overview

Areas of interest: dear receptors, caspase regulation, and gd T cell function in infection and autoimmunity

Dr. Budd's group examines the role of death receptors, such as Fas (CD95), and their downstream caspases in apoptosis and regulation of the immune response. Fas-deficient humans and mice develop an autoimmune disease resembling lupus, as well as profound enlargement of lymph nodes. Dr. Budd is studying the origin of the lymphocytes that accumulate in the absence of Fas-induced death. His group is also examining the Fas signal pathway and has made the paradoxical discovery that caspase-8 is required not only for cell death by Fas, but also to initiate proliferation of T lymphocytes. The switch between cell death and growth appears to be regulated by the caspase-8 paralogue, c-FLIP. Current studies are focused on determining how and where in a cell caspase activity is controlled during cell growth versus cell death. As caspase-8 and c-FLIP are ubiquitously expressed, they are likely to regulate cell growth and death in many cell types. 
 

Programs & Projects

Dr. Budd’s group also investigates the function of gd T cells in Lyme arthritis. Lyme disease is the most common vector-borne disease in the U.S. It is caused by the spirochete, Borrelia burgdorferi, that is transmitted by the tick, Ixodes scapularis. We have observed that an unusual and small subpopulation of T lymphocytes known as gd T cells accumulate in the joint fluid in patients with Lyme arthritis. These gd T cells respond to lipopeptides from B. burgdorferi. Our findings to date suggest a model whereby Borrelia lipopeptides bind to Toll-like receptor 2 on antigen presenting dendritic cells, which then upregulate surface molecules recognized by the gd T cells, such as the MHC-like molecules CD1b and MICA. This results in expression by the gd T cells of very high levels of surface FasL, and intense cytolysis of other neighboring T cells. However, due to high levels of c-FLIP in dendritic cells, they are not only resistant to Fas-induced death, but are activated by Fas ligation.

The Fas-deficient lymphoproliferative (lpr) mouse develops an autoimmune disease resembling human lupus, as well as profound enlargement of lymph nodes. We are studying the origin and cause of the lymphocytes that accumulate in the absence of Fas-induced death. In parallel studies, we are examining the alterations in Fas signaling caused by its natural inhibitor, c-FLIP. FLIP-transgenic mice manifest T cell hyperproliferation and a Th 2 cytokine bias. FLIP-Tg mice manifest worse allergic airway disease. We are studying how c-FLIP alters the signaling of T cells by associating with TRAF2 and RIP1 to augment activation of NF-B, and with Raf-1 to increase ERK activation. We are also investigating the function of T cells in Lyme arthritis. Lyme Disease is the most common vector-borne disease in the U.S. It is caused by the spirochete, Borrelia burgdorferi, that is transmitted by the tick, Ixodes scapularis. We have observed that an unusual and small subpopulation of T lymphocytes known as T cells accumulate in the joint fluid in patients with Lyme arthritis. These T cells respond to lipopeptides from B. burgdorferi Our findings to date suggest a model whereby Borrelia lipopeptides bind to Toll-like receptor 2 on antigen presenting dendritic cells, which then upregulate surface molecules recognized by the T cells, such as the MHC-like molecules CD1b and MICA. This results in expression by the T cells of very high levels of surface FasL, and intense cytolysis of other neighboring T cells, especially Th2 CD4+ cells. However, due to high levels of cFLIP in dendritic cells, they are not only resistant to Fas-induced death, but are activated by Fas ligation.

The Function of the Death Receptor Fas in the Immune System

The laboratory is examining the signal pathways of Fas and its inhibitor, cFLIP, in murine models of autoimmunity and in human Lyme arthritis.

Fas (CD95) and c-FLIP signaling in the immune system

The Fas-deficient lymphoproliferative (lpr) mouse pictured above develops an autoimmune disease resembling human lupus, as well as profound enlargement of lymph nodes. We are studying the types of lymphocytes that accumulate in the absence of Fas-induced death. In parallel studies, we are examining the alterations in Fas signaling caused by its natural inhibitor, cFLIP. Ligation of Fas recruits the adaptor protein FADD, which then recruits the protease caspase-8. cFLIP is homologous to caspase-8 but lacks protease activity and hence is a competitive negative regulator of Fas-induced death. We have observed that cFLIP also connects to the MAP kinase ERK, and NF-kB pathways and can thus divert Fas death signals toward signal pathways associated with cell growth. We are examining this using overexpression of wild type and mutant forms of cFLIP in cell lines and transgenic mice.

The function of gamma/delta T cells in Lyme arthritis

Lyme Disease is the most common vector-borne disease in the U.S. It is caused by the spirochete, Borrelia burgdorferi, that is transmitted by the tick, Ixodes scapularis. We have observed that an unusual and small subpopulation of T lymphocytes known as gamma/delta T cells accumulate in the joint fluid in patients with Lyme arthritis. These gamma/delta T cells respond to lipopeptides from B. burgdorferi Our findings to date suggest a model whereby Borrelia lipopeptides bind to Toll-like receptor 2 on antigen presenting dendritic cells, which then upregulate surface molecules recognized by the gamma/delta T cells, such as the MHC-like molecules CD1b and MICA. This results in expression by the gamma/delta T cells of very high levels of surface FasL, and intense cytolysis of other neighboring T cells, especially Th2 CD4+ cells. However, due to high levels of cFLIP in dendritic cells, they are not only resistant to Fas-induced death, but are activated by Fas ligation.