Defective lymphocyte chemotaxis in beta-arrestin2- and GRK6-deficient mice.

The overall goals of the Patel laboratory are two-fold: 1) to define the mechanisms of inflammation, focusing on signaling through G protein coupled receptors, for the purpose of identifying novel therapeutic targets for immunologic diseases; and 2) to define the role that T cell education in the thymus plays in diseases of disordered immunity such as autoimmune diseases and primary immunodeficiency syndromes.

1. Roles of Membrane-Tethered Chemokines in Inflammation. Based on one of our primary hypotheses that the critical step that regulates leukocyte migration from the circulation into tissues is at the stage of firm adhesion of a rolling leukocyte to the vascular endothelium, and that membrane-bound but not soluble chemokines are important mediators of this critical event, we identified a new pathway by which leukocytes can migrate into sites of inflammation. Fractalkine (FKN, CX3CL1), a unique endothelial cell surface molecule with chemokine and mucin domains that is expressed on IL-1 or TNF activated vascular endothelium, mediates the rapid capture, firm adhesion, and activation of circulating monocytes, CD8+ T cells and NK cells under physiologic shear stresses. The co-receptor for FKN is CX3CR1, a G-protein coupled receptor (GPCR). These findings have identified that both chemokines and GPCR can function as cell adhesion molecules. We are studying the structure-activity relationships of FKN and CX3CR1 and also testing the physiologic role of the FKN pathway of leukocyte migration to sites of inflammation. Using animal models (CX3CR1 and FKN-deficient mice), we are determining the roles of FKN and CX3CR1 in monocyte and natural killer cell function. Using FKN as a model system, we are also studying the functional roles of tethered vs. soluble chemokines in leukocyte trafficking and in inflammation.

2. Role of Thymic Education in Diseases of Disordered Immunity. The thymus is essential for developing a normal immune system. Abnormal T cell education in thymus can result in the production of autoreactive T cells that lead to autoimmune diseases such as diabetes mellitus and multiple sclerosis. The lack of a thymus can result in immunodeficiency. We are studying the roles of the thymus in various human diseases.

Role of the Thymus in Immune Reconstitution. T cell reconstitution after hematopoietic cell transplantation can occur either by peripheral expansion of passively transferred, mature T cells or by T cell education in the thymus and production of naïve T cells. Whether naïve T cells develop or T cell reconstitution occurs via expansion of mature T cells may predict whether the recipient can respond well to infections or the recipient's T cell repertoire is limited. We have, in collaboration with Dr. Rebecca Buckley, been studying T cell reconstitution in severe combined immunodeficiency (SCID) patients who have received haploidentical T cell-depleted stem cell transplants to answer basic questions about the human immune system.

Role of the Thymus in Autoimmunity. Escape from central tolerance in the thymus can result in autoimmunity, and we are interested in defining whether T cell education plays a role in the development of autoimmunity. Thymic dendritic cells (DC) are primarily responsible for deletion of autoreactive T cells, and defective negative selection by thymic DCs could result in a propensity to develop autoimmune disease. We have begun to study the biology of human thymic DCs and their roles in autoimmune processes.