The control of T and B lymphocyte function integrates different levels of molecular interaction. First, cell surface receptors are engaged, leading to activation of many physiological processes such as proliferation, cytokine production, or immunoglobulin synthesis. Inherent in this activation process is the tight regulation of cellular kinases and phosphatase which, in turn, determine the activity of both broadly-acting and specific transcription factors. There is increasing evidence that cellular activation events are also subject to control by the microenvironment. This includes features such as nutrient levels, hypoxia, pH, and the presence of reactive oxygen and nitrogen species. These environmental influences can shape cellular responses by altering the activity of kinases and phosphatases through modification of crucial amino acid residues, and by altering the ability of transcription factors to bind to specific DNA sequences. My laboratory has been studying the effect of oxidative stress on the development of immune responses.
The tripeptide glutathione (GSH) is the dominant intracellular thiol and a major determinant of the intracellular redox potential. It is transported out of cells down a three order of magnitude concentration gradient but cannot be recaptured in its intact form. The enzyme gamma glutamyltranspeptidase (GGT, CD224) is needed to remove the glutamyl group from GSH and allow the re-uptake of the component amino acids, particularly cysteine, for the re-synthesis of GSH.
We have shown that the expression of this critical enzyme is regulated on T and B lymphocytes. Naive T cells express little, if any, GGT. Its expression is turned on after several days of activation with anti-CD3, phorbol ester, or bacterial superantigen. It remains expressed at an intermediate level on cells that have achieved a memory phenotype. High levels of GGT are also seen on cells that have the capacity to migrate across an endothelial membrane, and on a subset of chronically stimulated cells from patients with rheumatoid arthritis.
We have shown that cells expressing higher levels of GGT have lower levels of intracellular reactive oxygen species (ROS) and higher levels of GSH. The expression of GGT has several effects on cellular functioning. When cells are thiol depleted or exposed to high levels of oxidative stress, GGT protects them from cell death. However, low levels of ROS actually protect cells from apoptosis by up-regulating NF-kB. GGT expression decreases the production of this transcription factor. Lastly, we have shown that GGT expression controls the cellular response to a physiological form of nitric oxide, S-nitrosoglutathione. This extremely stable form of NO causes cell cycle arrest in GGT expressing cells. Together, these data show an important role for GGT in lymphocyte physiology.
Current projects are focused on the role of oxidative stress/GGT on the early kinases and phosphatases involved in T cell activation, as well as their ability to polarize T cell responses to Th1 or Th2 types.
Our clinical research focuses on the evolution of normal immunity through a state of serologically defined "benign autoimmunity" to clinical disease such as systemic lupus erythematosus and rheumatoid arthritis. Using data from a large panel of patients and controls, we have developed methods to probe the humoral immune system for evidence of autoimmunity. We have shown that 27% of normal individuals have a detectable level of anti-nuclear antibody and 2.5% of normals have high levels of this antibody in their serum. Furthermore, these antibodies can be characterized using a newly developed array that tests for reactivity to 100 different antigens at a time.
In mice, variablilty in the SLAM/CD2 family of proteins determines the risk of autoimmunity. In collaboration with several other groups, we have identified genetic variants in the genes for the homologous proteins in lupus patients, suggesting that SLAM/CD2 may be part of a pathway to autoimmunity. We are combining the genetic and proteomic approaches to characterize persons at risk for development of autoimmune diseases.
RESEARCH INTERESTS
Role of oxidative stress in the regulation of immunity
Ability of the complement system to regulate immune responses
Genetics of human autoimmune diseases
Development of Data Sharing Methods in Biology
RECENT PUBLICATIONS
Quan-Zhen Li, Jinchun Zhou, Amy Wandstrat, Ferdicia Carr-Johnson, Valerie Branch, David Karp, Chandra Mohan, Edward Wakeland, and Nancy Olsen, "Protein array profiles for insights into systemic lupus erythematosus and incomplete lupus syndromes" Clin Exp Immunol, 147:60-70, 2007
A.E. Wandstrat, F. Carr-Johnson, V. Branch, H. Gray, A.-M. Fairhurst, A. Reimold, D. Karp, E.K. Wakeland, and N.J. Olsen, "Profiling populations at risk for systemic lupus erythematosus" J. Autoimmunity, 27:153-160, 2006
M.R. King, A.S. Ismail, L.S. Davis, and D.R. Karp, "Oxidative stress promotes polarization of human T cell differentiation towards a T helper 2 phenotype" J. Immunol, 176:2765-2772, 2006
Y. Lee, K.M. Haas, D.O. Gor, X. Ding, D.R. Karp, N.S. Greenspan, J.C. Poe, T.F. Tedder, "Complement component C3d-Ag complexes can either augment or inhibit B lymphocyte activation and humoral immunity in mice depending on the degree of CD21/CD19 complex engagement" J. Immunol, 175:8011-8023, 2005
C. Mineo, A.K. Gormley, I.S. Yuhanna, S. Osborne-Lawrence, L. L. Gibson, L. Hahner, R.V. Shohet, S. Black, J.E. Salmon, D. Samols, D.R., Karp, G.D. Thomas, P. W. Shaul, "FcγRIIB mediates C-reactive protein inhibition of endothelial NO synthase" Circ. Res, 97:1124-1131, 2005
SIGNIFICANT PUBLICATIONS
Susan A. Boackle, Margaret A. Morris, V. Michael Holers and David R. Karp, "Complement opsonization is required for presentation of immune complexes by resting peripheral blood B cells" J. Immunol,, 161:6537-6543
K.M. Haas, M. Hasegawa, D.A. Steeber, J.C. Poe, M.D. Zabel, C.B. Bock, D. Karp, D.E. Briles, J.H. Weis, and T.F. Tedder, "Complement receptors CD21/CD35 link innate and protective immunity during Streptococcul pneumoniae infection by regulating IgG3 antibody responses" Immunity, 17:713-724
Susan A. Boackle, V. Michael Holers, and David R. Karp, "CD21 augments antigen presentation in immune individuals" Eur. J. Immunol., 27:122-129
Karp, D. R., M. L. Carlisle, A. B. Mobley, T. C. Nichols, N. Oppenheimer-Marks, R. I. Brezinschek and V. M. Holers, "Gamma glutamyl transpeptidase is upregulated on memory T lymphocytes" International Immunology, 11:1791-1800, 1999
M.L. Carlisle, M. R. Wilkins, and D.R. Karp, "γ-Glutamyl transpeptidase activity alters the T cell response to oxidative stress and Fas-induced apoptosis" Int Immunol, 15:17-27, 2003
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