| Self-tolerance refers to the non-response of immune system to self- antigen. Self-tolerance allow immune system to recognize the―self‖and―non-self‖and avoid the immune response to―self‖, but only to the―non-self‖. Self-tolerance is a progress of acquisition. During the development, T cells acquire the tolerance to specific antigen and the property of tolerance need the induction of specific antigen. Even the tolerance to self-antigen needs this progress for no gene gives the specific information about what antigen is self or non-self.T cells play a central role in immune response and immune tolerance and most self-reactive T cells are deleted in thymus. Tissue restricted antigens (TRAs) expressed by thymic stroma cells play an important role in the deletion of self-reactive T cells. Thymic stroma cells include medullary thymic epithelial cells (mTECs), cortical thymic epithelial cells (cTECs) and dendritic cells (DC). Promiscuous gene expression is the expression of a highly diverse set of genes in thymic stroma cells, which otherwise are expressed in a strictly tissue-restricted fashion. mTECs express the most sorts of TRAs in all thymic stroma cells.The strain of NOD (non-obese diabetic) mice is an important model for type 1 diabetes (T1D). They develop T1D spontaneously. 1. The changes of endocrine glands pathology in NOD mice Infiltration of inflammatory cells was found in pancreas, salivary glands, and thyroids. No clear cortico-medullary junction exist in thymi of NOD mice. NOD mice showed distinct symptoms of autoimmune diseases and insulitis .2. The promiscuous gene expression and MHCII expression on mTECs2.1 Analysis the purity of primarily cultured TECs Immunochemistry essay of TECs from Balb/c and NOD mice showed that the purity and the size of TECs increased as culture time extended, and no distinct difference was found between Balb/c-mTECs and NOD-mTECs.2.2 MHCII expression level of mTECs MHCII expression NOD-mTEC was lower than that in Balb/c-mTEC, which could be one main reason of immune tolerance deficiency in NOD mice.2.3 The promiscuous gene expression on mTECs2.3.1 The compare of promiscuous gene expression between Balb/c and NOD mice mTECsThe expression of Ins, SP2, Igf2, and TG is much higher in Balb/c-mTECs than in NOD-mTECs at the 3rd day of cuture which indicated that some promiscuous gene expression in NOD mice was deficient.2.3.2 The changes of promiscuous gene expression with culture time extendedAt 4 time points (day 1, 3, 5, 8), the expression of Insulin, Igf2, SP2 showed that promiscuous gene expression is highest at the 1st day and declined as time extended in both Balb/c-mTECs and NOD-mTECs. At every time point, the expression level of each TRA by Balb/c-mTECs was higher than that in NOD-mTECs.3. The effects of promiscuous gene expression on mTEC to the apoptosis of T cells3.1 The proper mTECs to T cells ratio in the co-culture system Effects of mTECs/T cells (mTECs/T cells=1/2, 1/1, 2/1) cells to the apoptosis of T cells in co-culture system showed that the higher the mTECs ratio was the more necrosis and apoptosis T cells. The distribution of necrosis and apoptosis T cells was well-balanced when mTECs/T cells=1/2 and 1/1. We chose mTECs/T cells=1/1 as the ratio to do our next experiments. 3.2 The effect of promiscuous gene expression on mTECs to the apoptosis of T cellsWith the decline of promiscuous gene expression level, the proportion of necrosis T cells decreased, but the sum proportion of necrosis and apoptosis T cells remained the same.Conclusions1) Obvious pathology changes were found in NOD mice2) Expression of MHCII and various promiscuous genes was lower in NOD-mTECs than that in Balb/c-mTECs, which might be the main reason of T1D in NOD mice.3) The more the promiscuous gene expression, the higher ability of mTECs to induce T cell apoptosis.
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