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.
Late Complement Complex in T Cell Function and Cell Death.
Chauhan1, Anil, Atkinson3, John P., Moore2, Terry L.
Recently, complement systems role in T cell modulation has been suggested. Excessive complement activation results in cell death due to the formation of membrnae attack complex (MAC). Lysis of nucleated cells by MAC is explained by the "multi hit hypothesis" that suggests formation of a large number of holes. We tested this hypothesis in human naïve CD4+ T cells by in situ assembly of MAC using purified C5b-6, C7, C8 and C9. Scanning electron microscopy (SEM) and confocal imaging revealed formation of MAC on a single site. Thus, we hypothesize that due to strong affinity of C9 for membrane phopsholipids, sublytic MAC deposit resulted in reorganization of the T cell membrane. This resulted in the formation of a functional 'IS' synapse-like structure by lateral clustering of membrane rafts (MR). Thus, we explored the role of the structure formed by MAC in T cell physiology such as calcium channels, cell activation, proliferation and death.
MAC was assembled on human CD4+T cells by treating with equimolar ratio of purified late complement proteins along with fifteen molar excess of Alexa 594 labeled C9 protein. These cells were then examined for alteration in membrane structures by confocal and SEM. MR in these cells were localized using cholera toxin B-FITC. Cell proliferation was studied with CFSC labeling and T cell activation by traditional methods. Calcium mobilization was examined using Fura-2 dye.
Results & Conclusions:
Unlike present belief of multiple MAC generated holes in erythrocytes, in human T cells, MAC deposited on a single site. The SEM images showed a single hole surrounded by dense structures (A). These structures were also seen in confocal images (B).
The site of MAC was also the site of MR accumulation and formation of synapse-like structures. Signaling protein microclusters accumulated at this site and were phosphorylated. Such structures are also implicated in the function of NK cells. Sublytic doses of MAC trigger a number of events such as DNA synthesis, upregulation of cell cycle associated cyclins, CDK2, growth factors and proto-oncogenes such as NF-kB, c-jun, c-fos, jun-D, and protein kinase C. We have shown that in T cells these structures may participate in activation of the T cell receptor in the presence of immune complexes. However, in lytic doses of MAC, these structures that support cell function result in collapse of cell integrity, thus lysing the cell. Thus, we propose that ICs and MAC participate in the outcome of T cell differentiation by triggering and enhancing T cell activation. Complement activation and altered T signaling are observed in SLE. Here we link immune reactants observed in disease to the cells of adaptive immunity. Better understanding of these processes will allow us to delineate the disease process and design better therapeutic interventions.
To cite this abstract, please use the following information:
Chauhan, Anil, Atkinson, John P., Moore, Terry L.; Late Complement Complex in T Cell Function and Cell Death. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :1262