The B1a (CD5+) B-cells are the primary producers of natural antibodies that are self-reactive and polyreactive but usually non-pathogenic. However, in some circumstances, B1a B-cells contribute substantially to the immunopathogenesis of chronic systemic autoimmune diseases such as rheumatoid arthritis (RA), Sjogren's syndrome and systemic lupus erythematosus (SLE). B1a B-cells are a critical arm of the innate immune system and provides the first line of defense against a variety of bacterial and viral infections. The most prevalent B-cell malignancy, chronic lymphocytic leukemia (CLL) is CD5+ B-cell in origin. Curiously, HIV patients with progressive disease have paucity of CD5+ B-cells;in contrast, seropositive individuals with non-progressive disease have normal levels of B1a B-cells. This suggests the possibility that natural antibodies produced by CD5+ B-cells may be protective in HIV. The role of CD5 in the development, function and/or persistence of B1a B-cells remains an unresolved and controversial question. Since CD5 can negatively regulate signals initiated when the B-cell antigen receptor (BCR) is engaged by antigen, it is believed that its primary role in B1a B-cells is to control B-cell receptor activation from responding pathogenically to self antigen. However, this dogma is challenged by the fact that that CD5-/- mice do not develop spontaneous autoimmune disease. Our recent studies have led to that discovery that a major and probably dominant role of CD5, in addition to its inhibitory activity, is to promote survival. The survival activity of CD5 is mediated its unique interaction with CK2, a serine/threonine kinase that is a major positive regulator of multiple cellular prosurvival signaling cascades. In a counterpoint to the prosurvival activity mediated by activation of CK2, CD5 also has an immunoreceptor tyrosine inhibitory motif (ITIM) necessary for negative regulation of B-cell activation. The ITIM domain also provides prosurvival signals by attenuating B-cell activation and therefore activation-induced cell death. We suggest that CD5 regulates the B-cell response by two independent but complimentary pathways. To test this model, we have generated by gene targeting approach mice expressing CD5 with selective inability to activate the CD5-CK2 dependent prosurvival signaling cascade and mice lacking CD5-ITIM dependent negative regulatory activity. Using these unique animal models, and the new model we propose to develop, we will be in a position to (1) determine the role of CD5 in the development of B1a B-cells and its contribution to autoimmunity, (2) elucidate how CD5 regulates B-cell responses to T-independent antigens and T-dependent antigens and (3) dissect the molecular mechanism of CD5-dependent survival and inhibitory signals in normal B-cells. These studies using the novel animal models will enable us to resolve CD5 biology in B-cells. An important outcome of the proposed studies will be a major advancement in our understanding of regulatory pathways in innate B-cell responses to bacterial and viral pathogens and the development of targeting approaches for treatment of autoimmune diseases and leukemia.

Public Health Relevance

CD5+ B-Cells (B1a) B-cells are important in innate immunity, shaping the adaptive immune repertoire and in the immunopathogenesis of autoimmune diseases. The role of CD5 in the development of B-cells has been extensively interrogated, but remains unresolved;the goal of this proposal is to fill this gap in our understanding.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI076562-05
Application #
8277396
Study Section
Special Emphasis Panel (ZRG1-IMM-J (02))
Program Officer
Ferguson, Stacy E
Project Start
2008-06-01
Project End
2014-05-31
Budget Start
2012-06-01
Budget End
2014-05-31
Support Year
5
Fiscal Year
2012
Total Cost
$355,286
Indirect Cost
$110,261
Name
University of Alabama Birmingham
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
063690705
City
Birmingham
State
AL
Country
United States
Zip Code
35294
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