The main goal of our research is to define the antigen presentation requirements during inflammation within the central nervous system (CNS). Several different antigen presenting cells (APCs) participate in CD4 T cell-mediated immunity. We have focused on the role of two - B cells and dendritic cells (DCs) - that are highly relevant to the pathogenesis of multiple sclerosis (MS). To analyze distinct contributions of various APCs with specificity and efficiency, we have generated a new in vivo system for the conditional expression of major histocompatibility complex II (MHCII).
Our understanding of the basic pathogenic mechanisms of MS has been radically changed by the emergence of novel immune-based treatments that have specifically targeted B cells. Because there is strong clinical and experimental evidence that B cells contribute to MS via their role as APCs, we have used our conditional mouse system to explore the extent to which B cells alone can drive CD4 T cell auto-reactivity in vivo. In our preliminary studies, we have found that antigen presentation by B cells alone is not sufficient to support passive EAE resulting from transfer of encephalitogenic CD4 T cells unless B cells also express antigen receptor specific for cognate antigen. Currently, we are exploring the mechanisms by which B cells regulate CD4 T cell function during EAE.
In previous work, we have found that DCs are a minimally sufficient APC during both the initiation and propagation of neuro-inflammation. In part due to the accumulation of DCs within the CNS during EAE we hypothesize that their presence is essential to disease progression. We aim to identify the molecular and cellular mechanisms involved in DC localization to, and function within, the CNS. We are exploring the contribution of DC precursors that mobilize from the bone marrow prior to disease onset in EAE. Further, we are collaborating with Dr. Timothy Miller and his laboratory to define the micro-RNA signature of DCs before and after trafficking into the CNS during EAE. Our goals for this project are to identify the mechanisms by which DC precursors are recruited to the CNS and to determine the inflammatory signals that mobilize DC precursors from the bone marrow during EAE.
Myelin is targeted in MS by both innate and adaptive immune cells. We have observed a role for a vanilloid-type member of the Transient Receptor Potential (TRP) channel family, TRPV4 in EAE. In collaboration with Hongzhen Hu from the Center for the Study of Itch, we have observed in preliminary studies the expression of TRPV4 by immune cells. We are presently testing the requirement for innate immune cell expression of TRPV4 during neuro-inflammation using in vivo genetic manipulation of TRPV4. Additionally, we are pursuing studies using human specimens to explore whether TRPV4 is involved in the development of inflammatory demyelinating MS plaques.
In collaboration with Dr. Beau Ances and Dr. Greg Van Stavern, we have piloted a study to examine the cerebral changes resulting from anterior visual pathway loss in patients with optic neuritis. We are seeking to understand how the process of neuro-inflammation in patients with early forms of MS involving the optic nerve affects neuronal activity within visual pathways. We have utilized a new MRI technique, functional connectivity (fcMRI), to assess neuronal function in the visual system in patients who have suffered from inflammatory damage to the anterior visual pathway. The objective of this study is to determine whether the visual pathways in the brain are altered in the earliest stages of MS. Patients with optic neuritis have undergone evaluation with clinical measures, including vision tests, optical coherence tomography and visual function questionnaires; along with imaging of the brain using fcMRI and standard MRI sequences. In collaboration with Dr. Joe Culver, we are also pursuing correlates of this imaging technique in animal models of optic neuritis. Ultimately, assessment by this form of imaging may be useful in determining treatment response and severity of disease in patients with inflammatory demyelinating disease.
The goal of this project is to determine the contribution of innate immune cells, including microglia, macrophages and DCs, to the maintenance of axonal homeostasis and the initiation of axonal injury during autoimmune CNS inflammation. Damage to axons is a critical step underlying the clinical disability observed in MS. The mechanisms by which axons are injured and lost in MS remain unclear in spite of decades of descriptive associations between phagocytic innate immune cells and injured axons. The dynamic interactions between innate cells and axons during steady-state, as well as during various phases of immune targeting of myelin in MS, have not been demonstrated. In particular, the role of these innate cells in triggering axonal injury is not known. We hypothesize that microglia and DCs actively participate in axonal injury during EAE. In collaboration with Dr. Mark Miller, we are using two-photon microscopy (TPM) to test this hypothesis in several experiments. First, we are characterizing the phenotype of innate cells that reside in the CNS during steady-state conditions. The location, motility and general behavior of the different subsets of innate immune cells, including microglia and DCs, are being characterized using TPM. Second, we aim to determine if innate immune cells within the CNS initiate inflammatory axonal damage. A time series of reciprocal interactions between spinal cord axons and various innate cells is underway using TPM. Finally, we are evaluating the role of innate cell phagocytosis in mediating axonal damage in EAE by targeting the interactions between CD47 and signal regulatory protein alpha (SIRP alpha) that normally inhibit phagocytosis of tissue targets by innate immune cells.