Volume 14 Supplement 1
Death receptor-induced apoptosis signalling - essential guardian against autoimmune disease
© Strasser et al.; licensee BioMed Central Ltd. 2012
Published: 29 February 2012
The FasL/Fas system is critical for deletion of autoreactive and antigen-activated T and B cells. Accordingly, mutations in these proteins result in lymphadenopathy and autoimmunity in gld and lpr mutant mice, which lack functional FasL or Fas, respectively. Upon antigenic stimulation of T cells, FasL is sythesised, directed to and stored in secretory lysosomes followed by extrusion at the immunological synapse where it is rapidly downregulated by a metalloprotease, shedding the extracellular portion (sFasL) to prevent non-specific killing. It is unclear whether the pathology observed in gld mutant mice is due to the loss of the membrane-bound or the secreted form of FasL or both.
We have produced a panel of mutant FasL knock-in mice to address this question. In the first mutant strain the cytoplasmic and trans-membrane domains of FasL were replaced with the signal peptide from G-CSF. Activated T cells from these mutant mice can produce cytoplasmic but no membrane bound FasL and, interestingly, they are defective in FasL-mediated cytotoxic function and undergo significantly less activation-induced cell death upon re-stimulation with anti-CD3 antibodies than wt T cells. The extent of these defects is similar to that seen in FasL mutant gld T cells. With age these FasL mutant knock-in mice develop lymphadenopathy and splenomegaly and CD3+B220+CD4-CD8- T cells accumulate, similarly to what has been observed in gld and lpr mutant mice. In contrast to gld mice, the FasL mutant knock-in mice on the C57BL/6 background develop haemopoietic tumours and reticular cell sarcomas, suggesting that while membrane-bound FasL is the guardian against autoimmunity, secreted FasL may play a critical role in tissue damage and tumour suppression.
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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.