Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Costimulation Mediated Rescue of Superantigen Stimulated T Cells in Kawasaki Disease.

Wong2,  Aaron, Yeung1,  Rae S. M.

Hospital for Sick Children, Toronto, ON, Canada
The Hospital for Sick Children, Toronto, ON, Canada

Background:

Kawasaki Disease (KD) causes coronary arteritis and is the leading cause of acquired heart disease in children of the developed world. Evidence suggests that superantigens (SAgs) are involved in the pathogenesis of KD. Lactobacillus Casei cell wall extract (LCWE), a mouse model of KD, closely mimics human KD and SAg activity in LCWE directly correlates with its ability to induce coronary arteritis. Superantigens are potent T cell mitogens, initiating a tremendous inflammatory response with massive cytokine release characterized by production of tumor necrosis factor-alpha (TNFa). Our work suggests that enhanced costimulation can rescue SAg-stimulated T cells from apoptosis and thus could enable survival of autoreactive T cells which persist in our mouse model.

Objective:

To determine the mechanisms involved in costimulation mediated rescue of SAg-stimulated T cells.

Methods:

Splenocytes from C57BL/6, TNFR1 -/-, B7.2 -/-, and Cbl-b -/- mice were cultured in media containing various stimuli: Staphylococcal Enterotoxin B (SEB)-a prototypic SAg, recombinant TNFa (rTNFa), anti-CD28 antibody, CTLA4-Ig, and anti-TNFa antibody. Expression of B7.1, B7.2, Bcl-2, and Bcl-xl was determined by staining with fluorescent antibodies in flow cytometry experiments. In costimulatory rescue experiments, splenocytes were stimulated for 5 days and the levels of apoptosis within the SAg-reactive T cell population was determined by staining for TCRVb8 and annexin V. To determine the contribution of costimulatory molecules on T-cells versus antigen presenting cells (APC), cell populations were purified by magnetic bead separation, then mixed and co-cultured as described above.

Results:

Stimulation with SEB upregulated B7.2 expression in wildtype mice, but this response was diminished in TNFR1 -/- mice. Addition of rTNFa in the absence of SEB independently upregulated B7.2 expression. Enhancing costimulation with stimulatory anti-CD28 antibody rescued superantigen-reactive T cells from apoptosis in wild type and TNFR1-/-, but not Cbl-B -/- mice. Disrupting costimulation by blocking B7 with CTLA4-ig or neutralizing TNF increased apoptosis of SAg-reactive T cells. Mixing experiments with purified wildtype T cells and B7.2 -/- APCs exhibited no change in SAg-induced apoptosis when compared to cultures completely lacking B7.2. Increased expression of the anti-apoptotic markers Bcl-2 and Bcl-xl was found in cells receiving enhanced costimulation.

Conclusion:

TNFa plays an important role in regulating costimulation by regulating the expression of costimulatory ligand, B7.2, on APCs. The resultant B7.2/CD28 interaction is functionally relevant, leading to survival of SAg-reactive T cells. Rescued T cells had increased expression of anti-apoptotic markers Bcl-2 and Bcl-xl. As costimulation enables autoreactive cells to evade apoptosis and persist leading to persistent inflammation and tissue damage, this study lends additional mechanistic support to therapies that target TNF and costimulatory molecules for the treatment of KD. These principles are generalizable to many diseases where superantigens are implicated as triggers of a persistent immune response.

To cite this abstract, please use the following information:
Wong, Aaron, Yeung, Rae S. M.; Costimulation Mediated Rescue of Superantigen Stimulated T Cells in Kawasaki Disease. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :249
DOI: 10.1002/art.28018

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