Throughout development, maturation and activation, B cells are continuously exposed to two major opposing forces. The first is the drive to generate and maintain B cells with highly diverse immune receptors able to recognize the diversity of exogenous antigens. The second is the necessity to avoid damaging immune responses against self-components. The balance of these two forces ensures an inability to react to self-antigens while preserving defenses against pathogens. CD40-CD40L and BAFF-BAFFR cytokine pathways have been shown to play essential roles in B cell survival and differentiation. We investigated the regulatory mechanism of a novel adaptor molecule, termed Act1 in CD40 and BAFFR-mediated B cell survival. We found that CD40- and BAFF-mediated survival is significantly increased in Act1-deficient B cells. Consistent with this finding, Act1-deficient mice revealed a general increase in peripheral B cells, culminating in lymphadenopathy, splenomegaly, and the formation of autoantibodies. Act1 exerts its negative regulatory function in B cell survival through its direct impact on the immediate signaling events mediated by CD40 and BAFF. Act1-deficient B cells displayed enhanced CD40L- and BAFF-induced IkappaB phosphorylation and processing of NF-kappaB2(pl00/p52). Based on these findings, we hypothesize that Act1 is an important regulator for the homeostasis of B cells by attenuating CD40 and BAFFR signaling, modulating humoral immune responses. To test this hypothesis, we will first elucidate the mechanism by which Act1 negatively regulates the CD40- and BAFFR-mediated signaling (Specific Aim 1). We will then examine Investigate the physiological and pathological impact of the Act1-regulated pathways on B cell survival and humoral immune responses (Specific Aim 2). These proposed studies will provide us with the mechanistic insight for Act1's function, revealing how Act1 coordinately regulates CD40- and BAFFR-mediated pathways, thereby exerting its impact on B cell survival and modulating humoral immune responses. These findings will help us to elucidate the detailed regulatory mechanism for B cell homeostasis and opens new possibility to intervene the immune system.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI065470-03
Application #
7189893
Study Section
Cellular and Molecular Immunology - B (CMI)
Program Officer
Mallia, Conrad M
Project Start
2005-06-15
Project End
2010-02-28
Budget Start
2007-03-01
Budget End
2008-02-29
Support Year
3
Fiscal Year
2007
Total Cost
$362,679
Indirect Cost
Name
Cleveland Clinic Lerner
Department
Other Basic Sciences
Type
Schools of Medicine
DUNS #
135781701
City
Cleveland
State
OH
Country
United States
Zip Code
44195
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