Abstract
Introduction
Central tolerance eliminates self-reactive T cells preventing the T cell’s large receptor repertoire from recognizing self-antigens. Central tolerance is not complete allowing some self-reactive cells to survive and populate peripheral organs where tolerance mechanisms such as T regulatory cells (Tregs) ensure immune homeostasis and enforce quiescence of self-reactive cells. However, cell intrinsic mechanisms may change quiescent status of effector T cells and cause their proliferation and autoimmune disease. These self-reactive cells can be studied by using 2D2 mice, where T cells express a transgenic T cell receptor specific for the neural peptide myelin oligodendrocyte glycoprotein (MOG). 2D2 cells cause experimental autoimmune encephalomyelitis (EAE), which results in progressive paralysis. According to the literature without immunization with MOG and adjuvant about 4% will spontaneously develop paralysis. Paralysis occurs significantly higher in BMPR1𝛂 deficient 2D2 mice. Bone Morphogenic Proteins (BMPs) are a part of the TGF-𝛃 superfamily known for their essential cellular functions such as differentiation, proliferation, adhesion, migration and apoptosis. More recent evidence links their role in regulating immunological functions.
Methods
For BMPR1𝛂 analysis conditional knockout mice were bred by crossing BMPR1𝛂fl/fl mice with CD4cre, then GFP reporter mice. Genotyping mice was from DNA extracted in toe biopsies, was followed by PCR analysis of CD4cre, floxed alleles and GFP reporter constructs. Blood analysis included staining of CD4/CD8, Foxp3-GFP, and Ly5.1/Ly5.2 congenic markers to ensure 2D2 phenotype (V𝛂3.2 and V𝛃11), and allow donor/recipient tracking. Impact of BMP signalling in 2D2 T cells was studied by depleting environment of BMP ligands. This was achieved by adaptive transfer of dendritic cells expressing Noggin or Gremlin.
Results
The phenotype and functional status of 2D2 cells was analysed in recipient animals by flow cytometry. In vitro cultures assessed 2D2 cell proliferation and cell surface markers when cultured with MOG, spinal cord lysate, or bacterial lysate.
Conclusion
BMPs have been shown to be regulatory proteins and here we show that they influence onset of autoimmune disease. These data point to the importance of BMPR1𝛂 signalling for maintaining immune homeostasis.