Accelerated β-cell Destruction in Adoptively Transferred Autoimmune Diabetes Correlates With an Increased Expression of the Genes Coding for TNF-α and Granzyme A in the Intra-Islet Infiltrates Free

Autoimmune destruction of β-cells in nonobese diabetic (NOD) mice is greatly accelerated by adoptive cotransfer of syngeneic CD4⁺ and CD8⁺ T-cells from diabetic animals into newborn NOD mice. We followed, by in situ hybridization, the appearance of mRNA of the tumor necrosis factor (TNF)-α gene and, as a marker for activated cytotoxic T-cells, of the serine protease granzyme A gene in the cellular infiltrates generated by cell transfer at birth. Cells expressing the genes for granzyme A or TNF-α were seen in considerable numbers already on day 14, after adoptive transfer. These numbers gradually increased in the intra-islet infiltrates from day 14 through day 30 after adoptive transfer. Compared with our previous findings in NOD mice developing spontaneous insulin-dependent diabetes mellitus (IDDM) (Held W, MacDonald HR, Weissman IL, Hess MW, Mueller C: Genes encoding tumor necrosis factor α and granzyme A are expressed during development of autoimmune diabetes. Proc Natl Acad Sci USA 87:2239–xs2243, 1990), frequencies of cells with TNF-α and granzyme A mRNA were 2- and 12-fold higher, respectively, in transferred IDDM (trIDDM). TNF-α mRNA positive cells were predominantly found in the CD4⁺ T-cell subset of the pancreas-infiltrating cells, whereas granzyme A mRNA positive cells were mainly observed in the CD4⁻ T-cell subset. The effects of the observed enhanced TNF expression upon the pathogenesis of trIDDM are as yet unknown. One may speculate, however, that a local production of TNF -αexerts direct cytotoxicity upon β-cells and promotes lymphocyte traffic to the pancreatic islets, thus resulting in an increased frequency of antigen-specific cytotoxic cells (mainly CD8⁺ T-cells) within the islets of Langerhans. The burst of activated granzyme A gene-expressing cells at the onset of diabetes further suggests that enhanced cell-mediated cytotoxicity may significantly contribute to the accelerated loss of β-cells.