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.
Apoptotic Cell Bodies and Blebs Stimulate Self Reactive B-Cells Via Engagement of the BCR and Endosomal Toll-Like Receptors.
McCahan2, John, Green1, Nathanial, Marshak-Rothstein3, Ann
Apoptosis is a genetically programmed pathway of cell death that results in the condensation of a cell into sub-cellular particles. Under normal circumstances these are removed by surrounding cells and nearby phagocytes with a non-inflammatory effect. However, disruption of pathways involved in the removal of apoptotic cells has been shown to lead to signs of autoimmunity including autoantibody formation and tissue damage. The mechanisms that lead to the induction of auto-antibodies remain unclear. B cells from AM14 transgenic mice are a model of self reactive B-cells. They express an antigen receptor specific for IgG2aa/j and make a class of auto-antibodies known as rheumatoid factor (RF). It has been shown that immune complexes composed of IgG2a-chromatin or IgG2a-RNA can stimulate AM14 B-cells by the synergistic engagement of the antigen receptor and a member of the Toll-like receptor (TLR) family. Our purpose was to determine if apoptotic cells express auto-antigens that can stimulate self-reactive B-cells.
Keratinocyte and fibroblast cell lines were induced to undergo apoptosis by several methods including ultraviolet light exposure, etoposide, and serum starvation. In some experiments, cell surface proteins were biotinylated prior to the induction of apoptosis to nonspecifically label cell-surface-derived apoptotic debris. Subcellular particles were fractionated by differential centrifugation yielding two populations defined as apoptotic cell bodies and apoptotic blebs. Each fraction was analyzed by flow cytometry for the induction of apoptosis and autoantigen expression including nucleosomes, Ro, Smith antigen, and nucleoli. Immune complexes composed of subcellular particles bound by IgG2a autoantibodies were used to stimulate AM14 B cells. The contribution of TLR7 and TLR9 in this activation process was addressed by using cells from TLR-deficient mice.
A robust proliferative response was induced by immune complexes composed of apoptotic cell bodies and blebs bound by autoantibodies. This effect was enhanced with IFN-b priming and stimulation was mediated by binding of the B-cell receptor and engagement of either TLR7 or TLR9. Biotinylation experiments indicated that the autoantigens were associated with the cell membrane. By comparing the activity of immune complexes formed with the anti-biotin mAb and mAbs specific for defined autoantigens, we have been able to address the differential expression of autoantigens on apoptotic debris derived from diverse cell types.
Our findings suggest that self reactive B-cells can be stimulated by apoptotic cell bodies and blebs through a TLR mediated process.
To cite this abstract, please use the following information:
McCahan, John, Green, Nathanial, Marshak-Rothstein, Ann; Apoptotic Cell Bodies and Blebs Stimulate Self Reactive B-Cells Via Engagement of the BCR and Endosomal Toll-Like Receptors. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :736