We are interested in the molecular mechanisms which underlie the processes of lymphocyte activation and tolerance. Our particular areas of current focus are in lymphocyte signaling and interactions between innate and adaptive immune receptors.
The following is a summary of key projects ongoing in the lab :
How does TRAF3 regulate survival uniquely in B lymphocytes? How can this information be used to select more effective treatments for B cell malignancies?
Members of the tumor necrosis factor receptor (TNFR) superfamily participate in a large number of events that regulate cell activation and programmed cell death. A substantial majority of signals induced by receptors of this family are delivered via cytoplasmic (CY) adapter molecules belonging to the TNFR-associated factor (TRAF) family. It is now clear from work performed by our group and others during the past several years that TRAF3 can play diverse, even sharply contrasting roles in signaling by different receptors. Although whole-mouse deficiency in TRAF3 is lethal, we produced a conditional TRAF3-deficient mouse strain that permits us to assess the functions of TRAF3 in distinct cell types. Mice lacking TRAF3 specifically in B cells show dramatically increased B cell survival, with normal cell proliferation. This results in massively enlarged secondary lymphoid organs, autoantibody production and lymphoid infiltration of major organs, and development of B cell tumors as mice age. We have to date produced mice lacking TRAF3 in B lymphocytes, T lymphocytes, and dendritic cells. In all these cell types, TRAF3 deficiency results in constitutive activation of the ‘noncanonical’ or “NF-kB2” signaling pathway. However, although current dogma suggests that this explains the remarkably prolonged survival of TRAF3-deficient B cells, we found that NF-kB2 activation correlates with enhanced survival ONLY in B cells, and does not confer changes in survival on T cells or dendritic cells. This is consistent with the association of loss-of-function mutations in TRAF3 observed with B cell malignancies in humans, but not tumors in other cell types. We are thus investigating the molecular mechanisms by which TRAF3 deficiency regulates cell survival uniquely in B lymphocytes. This information could permit greater efficacy in designing treatments for B cell malignancies, as it can inform the targeting of non-proliferating cells that could survive standard chemotherapy.
What is the role of TRAF3 in signaling and function of T cells?
We also produced mice that lack TRAF3 specifically in T cells. Unlike B cells, TRAF3-deficient T cells have no alterations in survival. Instead, we found that these T cells show marked decreases in CD4+ and CD8+ T cell function to infection and immunization. Additionally, invariant NK T cell development and function are severely compromised in these mice, in a manner attributable to the reduced TCR signaling and upregulation of the transcription factor T-bet. In the absence of TRAF3, signaling through the TCR is compromised from the earliest measurable event, the activation of Src kinases. We also found that TRAF3 associates with the TCR complex. We are currently using multiple investigative strategies to explore this association, and how TRAF3 normally promotes TCR signaling and function. Key to this process appears to be blocking by TRAF3 of association with the TCR of the Src kinase inhibitor Csk. We are also investigating how TRAF3 regulates signaling through the IL-2 receptor by association with Jak molecules and the T cell phosphatase TCPTP. This regulation restrains IL-2 responses of thymic T regulatory cell precursors, and in the absence of T cell TRAF3, mice have an increased number of nTreg cells with elevated IL-2 responses.
Approaches to the design of better vaccination strategies.
The global human population is developing an increasing need for new and better vaccines, to combat both infectious and malignant disease. A limiting factor in human vaccine development has been the narrow selection of safe adjuvants, to increase the effectiveness of vaccines, and stimulate effective responses with fewer immunizations. Scientists have made tremendous advances in understanding how the components of adjuvants, distinct pathogen-associated molecular patterns (PAMPs), trigger specific receptors of the innate immune system. Of particular interest are ligands for receptors that recognize special features of viral or bacterial nucleic acids, as these ligands can be readily produced synthetically, without the safety concerns associated with purifying substances from large quantities of infectious microbes. This project focuses on gaining a more complete understanding of how receptors for microbial nucleic acids interact with receptors of the adaptive immune system in the activation of B lymphocytes, with the long-term goal of applying this knowledge to better strategies in vaccine development. B cells are now appreciated to play important roles in cytokine production and antigen presentation, and are highly TLR-responsive. What are the effects of interactive signals between adaptive and innate receptors on the function of B cells as antigen-presenting cells (APC)? We hypothesize that interactions between these receptor types will enhance the APC ability of B lymphocytes. This information will allow design of vaccines that maximize the efficacy of B cell activation, not only to produce antibodies and cytokines, but also to activate cellular responses as APC. Our findings to date show that B cell vaccines offer a viable alternative to dendritic cell vaccines in efficacy, and are much easier to obtain from the host and to manipulate in vitro. We are currently optimizing the stimuli used in B cell vaccination, and applying this information to vaccination in a melanoma tumor model.
Understanding the protective role of CD40 in diet-induced obesity.
We have studied the immune cell costimulatory signaling receptor CD40 for many years. We recently noticed that our colony of CD40 knockout (CD40KO) mice tend to become quite large as they pass mouse ‘middle age’. Upon further investigation, we discovered that they also have elevated blood glucose and decreased serum insulin. We embarked upon an initial set of studies to examine the role of CD40 in high-fat diet (HFD)-induced obesity (DIO). CD40KO mice gain significantly more weight on a HFD, and develop fatty livers, with both glucose and insulin intolerance. There is marked infiltration of macrophages and CD8+ T cells into the visceral adipose, but not the subcutaneous adipose tissue. The exacerbated DIO of CD40KO mice can be transferred to recipient mice with just CD8+ T cells, and requires TNF. These T cells express CD40 and also produce several chemokines at elevated levels. Current studies seek to understand the specific mechanisms by which CD40 protects against DIO normally, and how CD40 function in the intestinal immune system regulates the microbiota of the intestinal environment.