Clonal prevalence of T cells infiltrating into the pancreas of prediabetic non-obese diabetic mice.

The non-obese diabetic (NOD) mouse spontaneously develops T-cell-mediated autoimmune insulitis. We analyzed the clonotypes of T cell infiltrates of the NOD mouse islets using a new method we have developed recently, which consists of RT-PCR amplification of the CDR3 region of the TCR beta chain mRNA and subsequent single-strand conformation polymorphism (SSCP) analysis. NOD mice of 10-32 weeks of age were shown to accumulate oligoclonal T cells in the pancreas. To examine whether each T cell clone stays in a small area of the pancreas or spreads over the whole pancreas, a pancreas was divided into two pieces, which were then subsequently analyzed in a pair by the above PCR-SSCP method. When a pair produces common bands with the same mobility in SSCP gel, they are likely to represent the presence of the same T cell clones between these two parts of the pancreas. Aged mice (24-32 weeks old) with severe insulitis obviously produced more common bands for most of the Vbeta subfamilies than younger mice (10 weeks old) with only periinsulitis. DNA sequencing verified that these common bands have the same TCR junctional sequences, suggesting that they were derived from the same T cell clones. These results suggest that clonal prevalence of T cells infiltrating into the pancreas occurs in the late stage of insulitis development and that a limited number of T cell clones finally predominate over the whole pancreas.