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.


The Influence of Regulatory T-Cell Deficiency and Endogenous Muscle Tissue Antigens on the Development of Inflammatory Myopathy in Mice.

A. Young,  N., Sharma,  R., Kaffenberger,  B., Friedman,  A., N. Jarjour,  W.

Background:

Myositis is characteristically associated with an inflammatory process that results in pronounced muscle weakness. Myositis is observed in some regulatory T-cell (Treg) deficient mouse models. Scurfy mice lack Treg due to mutation in the X-linked forkhead box P3 (Foxp3) and develop multi-organ inflammation with little inflammation involving muscle tissue. Multiorgan inflammation but not muscle inflammation could be induced in RagI knockout (KO) recipient mice upon intravenous (IV) or intraperitoneal (IP) adoptive transfer of Scurfy lymph node (LN) cells. However, injecting scurfy cells intramuscularly (IM) induces severe inflammation in skeletal muscle suggesting that release of muscle antigen due to injury is a predisposing factor in triggering of muscle inflammation. To investigate the role of muscle antigens and Treg deficiency in the development of muscle inflammation, we crossed scurfy mice with synaptotagmin (Syt) VII deficient mice. The Syt VII mutation results in impaired membrane resealing and has been shown to lead to limited inflammation of muscle.

Methods:

Syt VII KO mice were bred with scurfy mice to produce Syt VII/Foxp3 double KO males. Genotyping was performed by PCR analysis of tail clippings and tissue was collected to analyze by H&E staining. LN cells from double KO or Foxp3 single mutant mice were used for injection into RagI KO males through IM and/or IP routes. In conjunction with the IP injection, some mice received muscle cell extract along with LN cells from scurfy mice. Skeletal muscle tissue was collected and analyzed as above.

Results:

Double KO mice with Syt VII/Foxp3 mutations developed more severe myositis compared to mice with either mutation alone. Furthermore, IP adoptive transfer of double KO LN cells induced dramatic myopathology in RagI KO recipients. Conversely, a notably limited infiltrate was seen in the skeletal muscle of Rag1 KO mice that received LN cells from Syt VII sufficient scurfy mice. The muscle antigen effect was then examined through IP adoptive transfer of scurfy LN cells into RagI KO recipients with and without muscle tissue cell extract. These results were compared to RagI KO recipients of scurfy LN cells by IM injection, which readily exhibit severe muscle inflammation. Inflammatory myopathy could only be induced in the RagI KO recipients through IP injection of scurfy LN cells if the mice were co-injected with muscle extract.

Conclusions:

This mouse model of myositis illustrates the interplay between two genetic defects in establishing a robust inflammatory process involving the muscle and that regulatory T cells are critical in limiting inflammation in muscles. The results suggest that endogenous muscle tissue antigen exposure either through injection of muscle extract or through leakage of endogenous antigen due to Syt VII mutation is essential in priming autoreactive cells. We have established a novel, reproducible model to study myositis that will be useful to define new autoantigens. Furthermore, extensions of this model can be used to investigate autoimmune phenomena that are triggered by extrinsic factors such as ultraviolet light or exposure to certain drugs.

To cite this abstract, please use the following information:
A. Young, N., Sharma, R., Kaffenberger, B., Friedman, A., N. Jarjour, W.; The Influence of Regulatory T-Cell Deficiency and Endogenous Muscle Tissue Antigens on the Development of Inflammatory Myopathy in Mice. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :1374
DOI: 10.1002/art.29140

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